title: Classification of GABA receptors in snail neurones.
abstract: The present study aimed to elucidate the pharmacological features of GABA receptors on identifiable neurones of Achatina fulica Férussac by testing the effects of GABA analogues, muscimol, (+/-)-baclofen, (-)-beta-hydroxy GABA and those conformationally fixed in either the extended or folded form of carbon chain, such as trans- and cis-isomers of (+/-)-2-(aminomethyl)cyclopropane-1-carboxylic acid [+/-)-cyclo-GABA-extended and (+/-)-cyclo-GABA-folded) and trans-4-amino-crotonic acid (GABA-extended). The giant neurones used were TAN, d-LPeLN, v-VNAN, v-LCDN and RPeNLN. The minimum effective concentrations (MEC) of these compounds to produce hyper- or depolarization of the membrane potentials of the neurones were determined, and the effective potency quotient (EPQ) of each compound vis-à-vis that of GABA was calculated for each neurone. The GABA receptors in these neurones were classified into the muscimol I, muscimol II and baclofen types. The muscimol I (TAN and d-LPeLN) and muscimol II (v-VNAN and v-LCDN) receptors were respectively hyperpolarized and depolarized by GABA and muscimol but were insensitive to (+/-)-baclofen. These muscimol receptors are inferred to accept GABA in an extended form of its carbon chain, since muscimol, conformationally fixed in this form from C-1 to C-4, was quite effective. Muscimol was more potent on the muscimol II receptors (MEC: 3 X 10(-7)-3 X 10(-6) M; EPQ: 30-10) than on the muscimol I type (MEC: 3 X 10(-5)-10(-4) M; EPQ: 1-0.3).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, Gifu University School of Medicine, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Yongsiri
authors.forename: K
authors.initials: K
authors.lastname: Funase
authors.forename: H
authors.initials: H
authors.lastname: Takeuchi
authors.forename: K
authors.initials: K
authors.lastname: Shimamoto
authors.forename: Y
authors.initials: Y
authors.lastname: Ohfune
mesh_terms: D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009118:Muscimol / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000378:metabolism; D012908:Snails / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D011963:Receptors, GABA-A; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D001418:Baclofen