Physiological roles of gamma-aminobutyric acid (GABA) on isolated human fallopian tube smooth muscle activities

Abstract

To determine whether GABA affects the contractile response of the longitudinal human fallopian tube smooth muscles, if so, which receptor is responsible for the contractility of the tube and what the mechanism of the action is, therefore studying of the isolated human fallopian tube under isometric condition was established. GABA and related substances, muscimol and baclofen did not alter the response to electrical transmural stimulation and exogenous norepinephrine. In contrast, GABA and its agonists neither affected the frequency and amplitude of spontaneous contraction nor under a combination of adrenergic and cholinergic blockers conditions. Whereas ACh produced the increasing of the frequencies of contraction. Forces of contraction produced by ACh-induced was augmented by 10 -3 M GABA and 10-5 M muscimol, but not baclofen, the values of per cent contraction (mean ± 2SE) being 143.74±36.24 and 155.08 ± 2.60 rise in ACh-induced contraction, respectively. Pretreatment of tissues with 10-5 M bicuculline antagonized the enhancing effect of GABA as well as that of muscimol. These results suggested that GABA presumably is a facilitatory modulator of parasympathetic neurotransmission, not of sympthetic neurotransmission and that the effect is exerted by activation through GABA-A receptors. The precise mechanisms of the modulatory effect of GABA remain to be elucidated.