Activation of GABA_AReceptor/Cl⁻Channel and Capacitation in Rat Spermatozoa: HCO₃⁻and Cl⁻are Essential

Abstract

This study was designed to determine whether HCO 3 À and Cl À are required for the activation of the GABA A receptor/Cl À channel (GBRC) by GABA and the subsequent capacitation of rat sperm. Spermatozoa from adult Sprague Dawley rats were incubated in four different media: modified complete rat fertilization medium (mRFM), Cl À -deficient (Cl À -DF) mRFM, HCO 3 À -DF mRFM, andCl À -DF HCO 3 À -DF mRFM, with or without GBRC agonists (GABA and progesterone) or GBRC antagonists (bicuculline and picrotoxin) for 0-6 h under capacitating conditions. Sperm capacitation and hyperactivation were assessed by chlortetracycline staining and computer-assisted sperm analysis, respectively. The results showed that GABA added to the mRFM accelerated capacitation and hyperactivation, followed by increase in the acrosome reaction, reaching maximum value after 5 h. Progesterone also accelerated sperm capacitation and hyperactivation. Bicuculline and picrotoxin, antagonists of GABA, blocked the effects of both GABA and progesterone acceleration of sperm capacitation and hyperactivation. Sperm capacitation required both Cl À and HCO 3 À . These results indicate that activation of GBRC may contribute to sperm capacitation and hyperactivation, and that both HCO 3 À and Cl À are essential. This is the first report of a close relationship between HCO 3 À /Cl À transport and the activation of GBRC in rat sperm capacitation and hyperactivation.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

“…Other cellular ligands can induce the AR such as progesterone (31, 55, 355, 506), ␥-aminobutyric acid (GABA) (280,355,559), glycine (301), EGF (133), ATP (339,442), acetylcholine (66), and sphingosine-1-phosphate (495). The role of many of these "alternative" agonists is not clear.…”

Suppression of Progesterone-enhanced Hyperactivation in Hamster Spermatozoa by γ-aminobutyric Acid

“…Moreover, P-enhanced hyperactivation is competitively suppressed by 17β-estradiol (E) [18]. In rat spermatozoa, P and GABA increase hyperactivation through the GABA A receptor/Cl - channel [19]. …”

“…In humans, rams and rats, GABA appears to increase sperm hyperactivation via the GABA A receptor/Cl - channel [19,20,21,22]. Because the GABA A receptor is the Cl - channel, it is thought that hyperactivation is increased through activation of the Cl - channel and hyperpolarization by Cl - influx [19, 20].…”

Cl− Channels and Transporters in Sperm Physiology

“…For example, Ritta et al established that this neurotransmitter plays a role in the regulation of motility in bovine and human sperm (Ritta et al 2004 ;Ritta et al 1998 ). In rat sperm, GABA and progesterone accelerated the process of capacitation and hyperactivated motility, effects that were inhibited by bicuculline and picrotoxin (Jin et al 2009 ). Additionally, it has been shown that GABA can induce the AR (Puente et al 2011 ;Shi et al 1997 ) and also that GABA A receptors can modulate the response to progesterone in these cells (Hu et al 2002 ;Ritta et al 1998 ;Shi and Roldan 1995 ;Turner et al 1994 ).…”

“…Polymerase chain reaction (PCR) and immunocytochemistry studies revealed the presence of GABA A and GABA B receptors in spermatogenic cells, and patch-clamp studies showed that GABA application to round spermatogenic cells induced an inward Cl − current (Kanbara et al 2011 ). The presence and function of GABA A receptors in sperm from different species have been explored by several laboratories (Jin et al 2009 ;Meizel 1997 ;Puente et al 2011 ;Wistrom and Meizel 1993 ). For example, Ritta et al established that this neurotransmitter plays a role in the regulation of motility in bovine and human sperm (Ritta et al 2004 ;Ritta et al 1998 ).…”