1685403

Effects of dihydroavermectin B1a and analogs on stretcher muscle of the lined shore crab, Pachygrapsus crassipes.

Article date: 1991/1/1

PubMed ID: 1685403

Journal name: Comparative biochemistry and physiology. C, Comparative pharmacology and toxicology (ISSN: 0742-8413)

ABSTRACT

1. Dihydroavermectin B1a (DHAVM, Ivermectin) at 1 microM reduces excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs, respectively) in stretcher muscle fibres of the lined shore crab, Pachygrapsus crassipes. IPSPs decline faster and more extensively than EPSPs and, unlike EPSPs, do not recover upon replacement of DHAVM with picrotoxinin-containing medium. 2. Intracellular recordings show DHAVM reduces membrane resistance (Rin) and hyperpolarizes muscle fibres in a concentration-dependent manner, beginning at 10 nM. The rate and magnitude of DHAVM effects on Rin mirror its effects on EPSPs. 3. The decline in Rin due to DHAVM is sustained over time (i.e. there is no tendency for desensitization); it is also irreversible and not affected by coadministration of 1 mM gamma-aminobutyric acid (GABA), 0.1 mM bicuculline methiodide or addition of 20 mM Co2+ to the recording medium. 4. Replacement of DHAVM-containing medium with medium containing Cl- channel blockers (picrotoxinin or lindane) results in partial recovery of Rin, while channel blockers specific for other ions (TTX, TEA, 4-AP or verapamil) are without effect. The decline of Rin following application of DHAVM is attenuated in Cl(-)-free medium. 5. Results of tests using compounds structurally related to DHAVM reveal that relatively minor changes in the molecule often reduce biological activity significantly. Removal of one sugar, for instance, results in a ten-fold reduction in potency. 6. In general, avermectins that stimulate conductance in shore crab muscle also possess anthelmintic activity at similar concentrations, based on studies using the free-living nematode, Caenorhabditis elegans.(ABSTRACT TRUNCATED AT 250 WORDS)

This document is available from: http://directlinks.cc/files/muscimol/1685403.pdf

Author List: Bowman J W, Lee B L, Whaley H A, Thompson D P

Publication Types: Comparative Study; Journal Article

Substances mentioned in the article: Anthelmintics; Chlorides; Picrotoxin; Muscimol; Cobalt; bicuculline methiodide; gamma-Aminobutyric Acid; Ivermectin; picrotoxinin; Bicuculline;

Mesh terms: Animals; Anthelmintics/pharmacology; Bicuculline/analogs & derivatives; Brachyura/drug effects; Caenorhabditis/drug effects; Chlorides/pharmacology; Cobalt/pharmacology; Dose-Response Relationship, Drug; Drug Interactions; In Vitro Techniques; Ivermectin/analogs & derivatives; Membrane Potentials/drug effects; Membranes/drug effects; Motor Endplate/drug effects; Muscimol/pharmacology; Muscles/drug effects; Picrotoxin/analogs & derivatives; Structure-Activity Relationship; Synapses/drug effects; Time Factors; gamma-Aminobutyric Acid/pharmacology;

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