In vitro effect of gamma‐aminobutyric acid on bovine spermatozoa capacitation

Abstract

Sperm capacitation is defined as the maturational changes that render a sperm competent for fertilization and occurs in the female reproductive tract. Identification of the factor/s that regulate sperm capacitation would allow the understanding of these phenomena. Among these factors, gamma-aminobutyric acid (GABA) has recently become as a putative modulator of sperm function. The aim of this study was to explore the presence of a GABAergic regulation of bovine sperm capacitation as well as the possible intracellular mechanisms involved. GABA was detected in fresh semen by a sensitive radioreceptor assay (spermatozoa, 0.064 +/- 0.003 nmoles/10(6) cells; seminal plasma, 23.21 +/- 1.16 nmoles/ml). Scatchard analysis of [(3)H]-muscimol binding to sperm membranes yielded a linear plot consistent with a single population of binding sites (K(d) = 3.87 nM, B(max) = 417 fmol/mg prot.). [(3)H]-muscimol specific binding to sperm membranes was significantly inhibited by the GABA A receptor (GABA A-R) antagonist bicuculline and by the agonists muscimol and isoguvacine. Addition of GABA to the incubation medium resulted in a concentration-dependent increase in the percentage of capacitated spermatozoa (chlortetracycline assay). We observed a significant increment on intracellular calcium and cyclic 3',5' adenosine monophosphate (cAMP) concentrations induced by GABA, being the cation influx abolished when the cell suspensions were coincubated with the antagonists bicuculline or picrotoxin. It is concluded that GABA induces sperm capacitation through an intracellular mechanism dependent on calcium influx and cAMP accumulation mediated by a specific GABA A-R.

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“…GABA A-receptor has been identified in human spermatozoa. In a recent study, the in vitro effect of GABA was studied on bovine spermatozoa capacitation [120]. It was observed that addition of GABA to the incubation medium results in a concentration-dependent increase in the percentage of capacitated spermatozoa.…”

GABA, progesterone and zona pellucida activation of PLA2 and regulation by MEK‐ERK1/2 during acrosomal exocytosis in guinea pig spermatozoa

“…In addition, high concentrations of GABA exist in seminal plasma [3,4]. This evidence suggests that GABA may exert a regulatory role in mammalian sperm function [5].…”

Insights into GABA Receptor Signalling in TM3 Leydig Cells

“…In early neurogenesis, GABA A stimulation was shown to depolarize, rather than to hyperpolarize cells, and this led to elevated Ca 2+ levels via opening of voltage-gated calcium channels [56,57,58,59]. Furthermore the second messenger cAMP has been implicated in neural and non-neural GABA A receptor signal transduction [29,30,31,32]. Importantly, in some cases the depolarizing GABA A currents have been reported to be very small (1–4 pA) [23], a fact that may be related to only few receptors on the cell surface.…”

“…The way of action of the GABA A receptor in immature neurons, contrary to mature neurons, is associated with depolarization of the cell membrane [14, 26, 27]. Despite the fact that there are many reports of non-synaptical GABA effects and actions, little is known about the subsequent intracellular pathways, but increased Ca 2+ levels and altering cAMP levels are two documented possibilities [24,28,29,30,31,32]. …”