N., and Bakry, N. M. (2006)

Moody, R. P., Parenteau, N. L., Ponec, M., Rovee, D. T., and Maibach, H. I. (1993). In vitro dermal absorption of pesticides: A cross-species comparison including testskin.
Chem Codes: Chemical of Concern: DZ Rejection Code: METHODS.

ISSN: 0731-3829

Descriptors: skin
Descriptors: absorption
Descriptors: in vitro
Descriptors: pesticides
Descriptors: species
Descriptors: comparison
Abstract: Dermal absorption studies with living animals have several disadvantages. The present study reports the use of our automated in vitro dermal absorption (AIDA) procedure developed inhouse as a potential alternative to in vivo testing. Finite-dose AIDA studies were conducted with the pesticides DEET, 2,4-D, Diazinon, and DDT, these compounds being chosen for their wide range of lipophilicities. Absorption (percentage recovery in receiver solution) in the human-derived tissue-cultured skin, Testskin, was similar to that in pig skin for three of the four test compounds. Testskin was 2.5 times more permeable than pig skin to 2,4-D. Continuous-dose AIDA studies conducted with the swimming pool stabilizer, cyanuric acid (CYA), demonstrated minimal CYA absorption through rat, hairless guinea pig, human, and Testskin. Total cumulative absorption of CYA by 24 hr in Testskin and human skin was 0.02 mu g CYA/cm super(2) in both cases.
Conference: Symposium on Methodologies and in vitro Applications for Skin Culture Models, New York, NY (USA), 12 Jun 1992
Language: English
English
Publication Type: Book Monograph
Publication Type: Conference
Classification: X 24221 Toxicity testing
Classification: X 24133 Metabolism
Subfile: Toxicology Abstracts

Moore, A. and Lower, N. (2001). The Impact of Two Pesticides on Olfactory-Mediated Endocrine Function in Mature Male Atlantic Salmon (Salmo salar L.) Parr. Comp.Biochem.Physiol.B 129: 269-276.

EcoReference No.: 67727

Chemical of Concern: ATZ,SZ,DZ; Habitat: A; Effect Codes: BCM,REP; Rejection Code: LITE EVAL CODED(ATZ,SZ),NO COC(DZ).

Moore, A. and Waring, C. P. (1998). Mechanistic Effects of a Triazine Pesticide on Reproductive Endocrine Function in Mature Male Atlantic Salmon (Salmo salar L.) Parr. Pestic.Biochem.Physiol. 62: 41-50.

EcoReference No.: 70210

Chemical of Concern: ATZ,DZ; Habitat: A; Effect Codes: BCM,PHY,REP; Rejection Code: LITE EVAL CODED(ATZ),NO COC(DZ).

Moorhouse, E. R., Gillespie, A. T., Sellers, E. K., and Charnley, A. K. (1989). The Compatibility of the Entomogenous Fungus, Metarhizium anisopliae with Horticultural Pesticides. In: N.R.McFarlane, Br.Crop Prot.Counc., Monogr.No.43, Progress and Prospects in Insect Control, Int.Conf., Sept.18-20, 1989, Reading, England, U.K. 251-252.

Chem Codes: Chemical of Concern: CYP,DDVP,TFR,DZ,BMY,CBD,Zineb Rejection Code: ABSTRACT.

MOORHOUSE ER, GILLESPIE AT, SELLERS EK, and CHARNLEY AK (1989). THE COMPATIBILITY OF THE ENTOMOGENOUS FUNGUS METARHIZIUM-ANISOPLIAE WITH HORTICULTURAL PESTICIDES. MCFARLANE, N. R. (ED.). BRITISH CROP PROTECTION COUNCIL MONOGRAPH, NO. 43. PROGRESS AND PROSPECTS IN INSECT CONTROL; INTERNATIONAL CONFERENCE, READING, ENGLAND, UK, SEPTEMBER 18-20, 1989. XI+273P. BRITISH CROP PROTECTION COUNCIL: SURREY, ENGLAND, UK. ILLUS. PAPER. ISBN 0-948404-32-9.; 0 (0). 1989. 251-252.

Chem Codes: Chemical of Concern: DZ Rejection Code: ABSTRACT.

BIOSIS COPYRIGHT: BIOL ABS. RRM ABSTRACT OTIORHYNCHUS-SULCATUS IMPATIENS ORNAMENTAL FRUIT FUNGICIDE CARBENDAZIM CHLORTHALONIL ETRIDIAZOLE ZINEB BENOMYL TRIFORINE PYRAZAPHOS INSECTICIDE ETRIDIAZOLE CYPERMETHRIN TRIFORINE DIAZINON DICHLORVOS HOSTATHION PROPAMOCARB PESTICIDE Congresses/ Biology/ Biochemistry/ Plants/Growth & Development/ Plants/Growth & Development/ Herbicides/ Pest Control/ Pesticides/ Arachnida/ Entomology/Economics/ Fruit/ Nuts/ Arachnida/ Entomology/Economics/ Trees/ Wood/ Arachnida/ Entomology/Economics/ Pest Control, Biological/ Arachnida/ Entomology/Economics/ Pest Control/ Arachnida/ Entomology/Economics/ Insecticides/ Pest Control/ Pesticides/ Fungi/ Mitosporic Fungi/ Plants/ Coleoptera

MOORMAN TB (1989). A REVIEW OF PESTICIDE EFFECTS ON MICROORGANISMS AND MICROBIAL PROCESSES RELATED TO SOIL FERTILITY. J PROD AGRIC; 2 14-23.
Chem Codes: Chemical of Concern: DZ Rejection Code: REVIEW.

BIOSIS COPYRIGHT: BIOL ABS. RRM REVIEW BACTERIA FUNGI ALGAE CROP RESIDUE DECOMPOSITION NUTRIENT CYCLING AGRICULTURE CROP INDUSTRY Biochemistry/ Nutrition/ Nutritional Status/ Soil Microbiology/ Plants/Growth & Development/ Soil/ Herbicides/ Pest Control/ Pesticides/ Bacteria/ Algae/ Fungi

Morales, Rogelio and Fernandez, Marta S. (2002). Interfacial Activation of Porcine Pancreatic Phospholipase A2 Studied with 7-Nitrobenz-2-oxa-1,3-diazol-4-yl-Labeled Lipids. Archives of Biochemistry and Biophysics 398: 221-228.
Chem Codes: Chemical of Concern: DZ Rejection Code: METHODS.

The interfacial activation of porcine pancreatic phospholipase A2 (PLA2) during the hydrolysis of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine liposomes at different temperatures has been monitored by fluorescence changes of the 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) lipid derivatives 1-palmitoyl-2-[6-[(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]dodecanoyl]-sn-glycero-3-phosphocholine (C12-NBD-PC) and 12-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)]dodecanoic acid (C12-NBD-FA) inserted in the substrate vesicles. These long-chain monitors, in contrast to the previously used C6-NBD-PC, detect latency times of PLA2 action, similar to those measured by the classic titrimetric, pH-stat method. Interestingly, hydrolysis of the host vesicles results in a decrease in fluorescence not only of C12-NBD-PC, a substrate analog, but also of product derivative C12-NBD-FA. Ultrafiltration experiments show that C12-NBD-FA does not migrate to the aqueous phase upon hydrolysis of the host liposomes. Besides, in a simulated hydrolysis experiment in which increasing proportions of palmitic acid and 1-palmitoyl-sn-glycero-3-phosphocholine were cosonicated with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, C12-NBD-PC fluorescence was insensitive to products, whereas C12-NBD-FA did show a decreased emission intensity as in the actual hydrolysis experiments. The phenomenon is triggered above a critical concentration of products (10 mol%) suggesting that cosegregation of NBD-FA (either added as such or generated by hydrolysis of C12-NBD-PC) and products may be related to the decrease in fluorescence. Phase separation should create microdomains of increased C12-NBD-FA surface density and cause concentration quenching. In addition, and taking into account that the NBD group may be located near the interfacial region, it is possible that in segregating with products, the fluorescent moiety of C12-NBD-FA becomes exposed to microenvironments of higher surface polarity, which further decreases its quantum yield. phospholipase A2/ interfacial activation/ NBD

Moreland D. E., Corbin F. T., Fleischmann T. J., and Mcfarland J. E. (1995). Partial Characterization of Microsomes Isolated from Mung Bean Cotyledons. Pesticide Biochemistry and Physiology 52: 98-108.
Chem Codes: Chemical of Concern: MTL,PPB Rejection Code: IN VITRO.

Microsomes isolated from excised cotyledons of 3-day-old, dark-grown, mung bean (Vigna radiata, L., cv Berken) seedlings metabolized two endogenous substrates (cinnamic acid and lauric acid), three organophosphate insecticides (diazinon, isazofos, and methidathion), three acetamide herbicides (metolachlor, CGA-24704, and alachlor), and bentazon. Cinnamic acid was aryl hydroxylated forming p-coumaric acid. Lauric acid was primarily hydroxylated at the terminal carbon ([omega]-hydroxylation). The three [alpha]-chloroacetamides were O-demethylated. With all three organophosphate insecticides, the phosphorothionate sulfur was oxidized to the corresponding oxon and the phosphoroester oxygen was cleaved in both diazinon and isazofos. Bentazon was aryl hydroxylated forming the 6-hydroxy derivative. The concentration of cytochrome P450 in the microsomal preparations was marginally enhanced by pretreatment of the seed with naphthalic anhydride (NA), but was markedly increased by subirrigation of NA-treated seed with ethanol and was additionally increased with the combination of NA, clofibrate, and ethanol. The extent of metabolism of only lauric acid paralleled the increases in cytochrome P450 content. The various seed/seedling treatments, however, did approximately double the rate of metabolism of the three organophosphates, the three chloroacetamides, and bentazon. Metabolism required a reduced pyridine nucleotide and was affected by several cytochrome P450 monooxygenase inhibitors (carbon monoxide, tetcyclacis, piperonyl butoxide, 1-aminobenzotriazole, and SKF-525A). The inhibitors differentially affected metabolism of the substrates. Microsomal oxidations from both untreated and inducer-treated tissue responded similarly to the inhibitors. The differential inhibitory responses suggest that metabolism may involve several monooxygenase isoforms.

Moreland D. E., Corbin F. T., Fleischmann T. J., and Mcfarland J. E. (1995). Partial Characterization of Microsomes Isolated from Mung Bean Cotyledons. Pesticide Biochemistry and Physiology 52: 98-108.
Chem Codes: Chemical of Concern: DZ Rejection Code: IN VITRO.

Microsomes isolated from excised cotyledons of 3-day-old, dark-grown, mung bean (Vigna radiata, L., cv Berken) seedlings metabolized two endogenous substrates (cinnamic acid and lauric acid), three organophosphate insecticides (diazinon, isazofos, and methidathion), three acetamide herbicides (metolachlor, CGA-24704, and alachlor), and bentazon. Cinnamic acid was aryl hydroxylated forming p-coumaric acid. Lauric acid was primarily hydroxylated at the terminal carbon ([omega]-hydroxylation). The three [alpha]-chloroacetamides were O-demethylated. With all three organophosphate insecticides, the phosphorothionate sulfur was oxidized to the corresponding oxon and the phosphoroester oxygen was cleaved in both diazinon and isazofos. Bentazon was aryl hydroxylated forming the 6-hydroxy derivative. The concentration of cytochrome P450 in the microsomal preparations was marginally enhanced by pretreatment of the seed with naphthalic anhydride (NA), but was markedly increased by subirrigation of NA-treated seed with ethanol and was additionally increased with the combination of NA, clofibrate, and ethanol. The extent of metabolism of only lauric acid paralleled the increases in cytochrome P450 content. The various seed/seedling treatments, however, did approximately double the rate of metabolism of the three organophosphates, the three chloroacetamides, and bentazon. Metabolism required a reduced pyridine nucleotide and was affected by several cytochrome P450 monooxygenase inhibitors (carbon monoxide, tetcyclacis, piperonyl butoxide, 1-aminobenzotriazole, and SKF-525A). The inhibitors differentially affected metabolism of the substrates. Microsomal oxidations from both untreated and inducer-treated tissue responded similarly to the inhibitors. The differential inhibitory responses suggest that metabolism may involve several monooxygenase isoforms.

Moreland, D. E., Corbin, F. T., and Mcfarland, J. E. (1993). Effects of safeners on the oxidation of multiple substrates by grain sorghum microsomes. Pestic Biochem Physiol 45 : 43-53.
Chem Codes: Chemical of Concern: MTL,PPB Rejection Code: IN VITRO.

ABSTRACT: BIOSIS COPYRIGHT: BIOL ABS. Microsomes isolated from excised shoots of 3-day-old, dark-grown, grain sorghum (Sorghum bicolor (L.) Moench, Funk G522DR, and DK 41Y) seedlings metabolized cinnamic acid, lauric acid, metolachlor, bentazon, and diazinon, but did not metabolize triasulfuron or primisulfuron. Pretreatment of G522DR seed with safeners (naphthalic anhydride, dichlormid, flurazole, BAS 145138, oxabetrinil, fluxofenim, and benoxacor) resulted in enhanced metabolism of lauric acid, bentazon, and diazinon. However, metabolism of cinnamic acid was not affected and that of metolachlor was depressed by safener treatments. Microsomes isolated from DK 41Y seedlings had higher endogenous levels of oxidative activity for lauric acid and bentazon than microsomes isolated from G522DR seedlings. Metabolism required NADPH and was affected by CO and other cytochrome P450 monooxygenase inhibitors (tetcyclacis, piperonyl butoxide, 1-aminobenzotriazole, SKF-525A, and tridiphane). The inhibitors differentiall

KEYWORDS: Biochemical Studies-General
KEYWORDS: Biochemical Studies-Proteins
KEYWORDS: Enzymes-Physiological Studies
KEYWORDS: Metabolism-Energy and Respiratory Metabolism
KEYWORDS: Toxicology-General
KEYWORDS: Plant Physiology
KEYWORDS: Agronomy-Grain Crops
KEYWORDS: Agronomy-Weed Control
KEYWORDS: Pest Control
KEYWORDS: Economic Entomology-Chemical and Physical Control
KEYWORDS: Gramineae

Moreland D. E., Corbin F. T., and Mcfarland J. E. (1993). Effects of Safeners on the Oxidation of Multiple Substrates by Grain Sorghum Microsomes. Pesticide Biochemistry and Physiology 45: 43-53.

Chem Codes: Chemical of Concern: DZ Rejection Code: METABOLISM.

Microsomes isolated from excised shoots of 3-day-old, dark-grown, grain sorghum [Sorghum bicolor (L.) Moench. Funk G522DR, and DK 41Y] seedlings metabolized cinnamic acid, lauric acid, metolachlor, bentazon, and diazinon. but did not metabolize triasulfuron or primisulfuron. Pretreatment of G522DR seed with safeners (naphthalic anhydride, dichlormid, flurazole, BAS 145138, oxabetrinil, fluxofenim, and benoxacor) resulted in enhanced metabolism of lauric acid, bentazon, and diazinon. However, metabolism of cinnamic acid was not affected and that of metolachlor was depressed by safener treatments. Microsomes isolated from DK 41Y seedlings had higher endogenous levels of oxidative activity for lauric acid and bentazon than microsomes isolated from G522DR seedlings. Metabolism required NADPH and was affected by CO and other cytochrome P450 monooxygenase inhibitors (tetcyclacis, piperonyl butoxide, 1-aminobenzotriazole, SKF-525A, and tridiphane). The inhibitors differentially affected metabolism of the substrates. Only tetcyclacis strongly inhibited the metabolism of all substrates except cinnamic acid. Microsomal oxidations from both unsafened and safener-treated tissue responded similarly to the inhibitors. The differential inhibitory responses suggest that each substrate was probably metabolized by a different monooxygenase isoform.

Moreland, D. E., Corbin, F. T., and Mcfarland, J. E. (1993). Oxidation of multiple substrates by corn shoot microsomes. Pesticide Biochemistry and Physiology 47 : 206-214.
Chem Codes: Chemical of Concern: MTL,PPB Rejection Code: IN VITRO.

ABSTRACT: BIOSIS COPYRIGHT: BIOL ABS. Microsomes isolated from excised shoots of 3-day-old, dark-grown, corn (Zea mays L., Pioneer Hybrid 3245) seedlings metabolized two endogenous substrates (cinnamic acid and lauric acid), one insecticide (diazinon), and six herbicides (metolachlor, bentazon, CGA-152005, triasulfuron, primisulfuron, and nicosulfuron). Pretreatment of the seed with the safener naphthalic anhydride resulted in enhanced metabolism of all substrates except cinnamic acid. Metabolism required NADPH and was affected by several cytochrome P450 monooxygenase inhibitors (tetcyclacis, piperonyl butoxide, 1-aminobenzotriazole, SKF-525A, and tridiphane). The inhibitors differentially affected metabolism of the substrates. Tetcyclacis and piperonyl butoxide strongly inhibited the metabolism of all substrates except cinnamic acid. Microsomal oxidations from both unsafened and safener-treated tissue responded similarly to the inhibitors. The differential inhibitory responses suggest that metabolism may i

KEYWORDS: Cytology and Cytochemistry-Plant
KEYWORDS: Comparative Biochemistry
KEYWORDS: Biochemical Studies-Proteins
KEYWORDS: Enzymes-General and Comparative Studies
KEYWORDS: Metabolism-General Metabolism
KEYWORDS: Metabolism-Energy and Respiratory Metabolism
KEYWORDS: Toxicology-Environmental and Industrial Toxicology
KEYWORDS: Plant Physiology
KEYWORDS: Agronomy-Grain Crops
KEYWORDS: Gramineae

Moreland D. E., Corbin F. T., and Mcfarland J. E. (1993). Oxidation of Multiple Substrates by Corn Shoot Microsomes. Pesticide Biochemistry and Physiology 47: 206-214.

Chem Codes: Chemical of Concern: DZ Rejection Code: IN VITRO.

Microsomes isolated from excised shoots of 3-day-old, dark-grown, corn (Zea mays L., Pioneer Hybrid 3245) seedlings metabolized two endogenous substrates (cinnamic acid and lauric acid), one insecticide (diazinon), and six herbicides (metolachlor, bentazon, CGA-152005, triasulfuron, primisulfuron, and nicosulfuron). Pretreatment of the seed with the safener naphthalic anhydride resulted in enhanced metabolism of all substrates except cinnamic acid. Metabolism required NADPH and was affected by several cytochrome P450 monooxygenase inhibitors (tetcyclacis, piperonyl butoxide, 1-aminobenzolriazole, SKF-525A, and tridiphane). The inhibitors differentially affected metabolism of the substrates. Tetcyclacis and piperonyl butoxide strongly inhibited the metabolism of all substrates except cinnamic acid. Microsomal oxidations from both unsafened and safener-treated tissue responded similarly to the inhibitors. The differential inhibitory responses suggest that metabolism may involve several monooxygenase isoforms.

Morgan, M. K., Stout, D. M. II, and Wilson, N. K. (2001). Feasibility Study of the Potential for Human Exposure to Pet-Borne Diazinon Residues Following Lawn Applications. Bulletin of Environmental Contamination and Toxicology [Bull. Environ. Contam. Toxicol.]. Vol. 66, no. 3, pp. 295-300. Mar 2001.
Chem Codes: Chemical of Concern: DZ Rejection Code: HUMAN HEALTH.

ISSN: 0007-4861

Descriptors: Pets
Descriptors: Diazinon
Descriptors: Pesticides (organophosphorus)
Descriptors: Insecticides
Descriptors: Indoor environments
Descriptors: Pesticide residues
Abstract: The objectives of this study were 1) to investigate the potential for an indoor/outdoor pet dog to transport and translocate diazinon residues into a residence following a lawn application, 2) to determine if intimate contacts between a pet dog and occupants resulted in measurable exposures, and 3) to determine if a pet dog could be a good indicator of exposure following a lawn application of diazinon.
Language: English
Publication Type: Journal Article
Classification: X 24133 Metabolism
Classification: H 5000 Pesticides
Classification: R2 23060 Medical and environmental health
Subfile: Risk Abstracts; Health & Safety Science Abstracts; Toxicology Abstracts

Moriarty, Robert M. and Khosrowshahi, Jaffar S. (1986). A versatile synthesis of vicinal diazides using hypervalent iodine. Tetrahedron Letters 27: 2809-2812.

Chem Codes: Chemical of Concern: DZ Rejection Code: METHODS.

A convenient synthesis of vicinal diazides from olefins using C6H5IO/HOAc/NaN3 is described. A mechanism is proposed which accounts for the stereochemical outcome.

Morishita, M. (2001). Toxicity of Some Insecticides to Larvae of Flankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) Evaluated by the Petri Dish-Spraying Tower Method. Appl.Entomol.Zool. 36: 137-141.

EcoReference No.: 82021

Chemical of Concern: PRB,EMMB,THO,ACT,EFX,TDL,PIM,PHSL,PIRM,DMT,FNTH,MLN,DDVP,ACT,LUF,TCF,CYP,ES,SS,IMC,FVL,PMR,CBL,MOM,ALP,FNT,MDT,CPY,FF,DZ,BFT; Habitat: T; Effect Codes: MOR; Rejection Code: TARGET(DZ).

MORITA, M., YOSHINAGA, J., MUKAI, H., AMBE, Y., TANAKA, A., and SHIBATA, Y. (1997). Specimen banking at National Institute for Environmental Studies, Japan. CHEMOSPHERE; 34 1907-1919.

Chem Codes: Chemical of Concern: DZ Rejection Code: NO TOX DATA.

BIOSIS COPYRIGHT: BIOL ABS. The National Institute for Environmental Studies (NIES) in Japan has had more than fifteen years practical experience in specimen banking. Stored specimens are used for the assessment of long-term trends of pollutants. The use of new analytical techniques facilitates the finding of the pollutants of the past. Conservation of Natural Resources/ Ecology/ Air Pollution/ Soil Pollutants/ Water Pollution

Morita, Tomotsu and Lemone Yielding, K. (1977). Induction of respiratory deficient mutants in Saccharomyces cerevisiae by mono- and diazido analogs of ethidium. Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 56: 21-30.
Chem Codes: Chemical of Concern: DZ Rejection Code: NO COC.

Mono- and diazido analogs of ethidium when photolyzed with yeast cells were highly effective in inducing respiratory deficient (RD) mutants. The monoazide was more mutagenic, though slightly less photosensitive, and under the concentrations and conditions used, both required photolysis to be significantly mutagenic.Ethidium bromide (EB) competed with either its mono- or diazide analog for RD induction when applied before, but not after, the photolysis step. This suggested that the initial mutagenic binding sites for the azides were identical with those of EB.There was no self-rescue or recovery in azide mutagenesis in contrast to EB. Furthermore, recovery from azide mutagenesis could not be provoked by EB. This confirmed a simple competition between binding of EB and its azide analogs to account for the prevention by EB of the azide induced mutations.

Moritoki, H., Shinohara, Y., Yamauchi, M., and Ishida, Y. (1978). Effects of Cholinesterase Inhibitors on the Spasmogenic Action of Acetate Esters on Rat Uterus. Eur.J.Pharmacol. 47: 95-102.
Chem Codes: Chemical of Concern: DZ Rejection Code: IN VITRO.

Morris, Stephen J., Bradley, Diane, and Blumenthal, Robert (1985). The use of cobalt ions as a collisional quencher to probe surface charge and stability of fluorescently labeled bilayer vesicles. Biochimica et Biophysica Acta (BBA) - Biomembranes 818: 365-372.

Chem Codes: Chemical of Concern: DZ Rejection Code: METHODS.

Co2+ quenched the fluorescence of the lipid probes NBD-phosphatidylethanolamine (NBD-PE) and lissamine-rhodamine phosphatidylethanolamine (N-Rh-PE) incorporated into lipid vesicles, according to a collisional quenching mechanism in agreement with the Stern-Vollmer law. The quenching coefficient (Q) for NBD-PE, incorporated into uncharged phosphatidylcholine (PC) vesicles was 13.8 M-1. This value was equal to the quenching coefficient of water-soluble NBD-taurine in aqueous solution, indicating that Co2+ was readily accessible to the outer surface of PC vesicles. In phosphatidylserine-phosphatidylethanolamine (PS-PE) (1:1) vesicles, quenching was also proportional to Co2+ concentration but Q was 114 mM-1, some 8000-fold smaller. Using the Gony-Chapman-Stern model we demonstrated that the surface density of Co2+ bound to lipid was linear with Co2+ concentration in the medium up to 7%. Co2+-associated phospholipid would in turn quench NBD-PE or N-Rh-PE by collisional quenching with lateral diffusion. We investigated the ability of Co2+ to permeate PS-PE (1:1) vesicles. Co2+ quenched fluorophores on the outer surface of large unilamellar vesicles, formed by reverse-phase evaporation. In small unilamellar vesicles Co2+ quenched probes on both outer and inner surfaces, indicating rapid permeation of the ions into the vesicles. Using stopped-flow rapid mixing, we measured the rate of influx of Co2+, and correcting for surface potential using the Gouy-Chapman-Stern model, we calculated a permeability coefficient of 10-12 cm/s for Co2+ concentrations below 300 [mu]M. Above this concentration, there was a very steep rise in the permeability coefficient, indicating that binding of Co2+ induces defects in the bilayer of these vesicles. This may be related to the ability of the vesicles to undergo membrane fusion. A method for calculating the membrane surface potential from Co2+ quenching data is presented. Unilamellar vesicle/ Co2+/ Fluorescence labeling/ Membrane surface potential/ Fluorescence quenching/ Bilayer defect