Bicarbonate/CO2, an effector of capacitation, induces a rapid and reversible change in the lipid architecture of boar sperm plasma membranes

Abstract

Bicarbonate/CO2 is believed to be the key in vitro effector of sperm capacitation, a process which induces major changes in the sperm plasma membrane in preparation for fertilization. In a flow cytometric study, we examined the effect of bicarbonate on boar spermatozoa using merocyanine, an impermeant lipophilic probe which binds to plasma membranes with increasing affinity as their lipid components become more disordered. We found that bicarbonate causes a rapid increase in the ability of live boar spermatozoa to bind merocyanine. First detected about 100 sec after exposure to bicarbonate and largely complete by 300 sec, this increase appears to result from individual cells within the sperm population switching from a low merocyanine-binding state to a high binding state. The majority of live spermatozoa are capable of responding in this way, and do so in proportion to bicarbonate concentration, half-maximal response being induced by about 3 mM bicarbonate; however, overall population response varies greatly between ejaculates. Increased merocyanine stainability is observed over the whole surface area of the cell, and is reversible both with respect to temperature (it is only manifested above 30 degrees C) and with respect to presence of bicarbonate. A similar effect can be induced by phosphodiesterase inhibitors such as isobutylmethylxanthine, and enhanced by a permeant cyclic nucleotide analogue. We conclude that bicarbonate causes a major alteration in sperm plasma membrane lipid architecture, apparently by perturbing enzymic control processes. This novel action of bicarbonate may represent an initial permissive event in the capacitation sequence.

Involvement of multimeric protein complexes in mediating the capacitation-dependent binding of human spermatozoa to homologous zonae pellucidae

“…Recent advances have revealed that in human spermatozoa, capacitation may be initiated by engagement of surface receptors (Nixon et al, 2006) and the subsequent induction of complex signaling pathways that ultimately converge to promote an impressive upregulation of tyrosine phosphorylation across myriad target proteins (Leclerc et al, 1996(Leclerc et al, , 1998Lefievre et al, 2002;Mitchell et al, 2008;Visconti et al, 1995aVisconti et al, , 1995b. While the precise mechanisms remain to be unequivocally established, these biochemical changes appear causally linked to the surface remodeling events that allow spermatozoa to adhere to the ZP (Cross, 2003;Gadella et al, 2008;Harrison et al, 1996;Harrison and Gadella, 2005;Myles and Primakoff, 1984;Yanagimachi, 1994).…”

The impact of spermatozoa preincubation time and spontaneous acrosome reaction in intracytoplasmic sperm injection: a controlled randomized study

“…Bicarbonate plays a major role in the activation of sperm cells (43). High levels of bicarbonate induce activation of adenylate cyclase, one of the key events in sperm capacitation that occurs in the lumen of the oviduct and is virtually absent in epididymal and seminal plasma (44). Under normal conditions, most of the freshly ejaculated spermatozoa are acrosome unreacted.…”

A Differential Mechanism Is Involved During Heparin- and Cryopreservation-Induced Capacitation of Bovine Spermatozoa

“…Capacitation allows spermatozoa to undergo the zona pellucida-induced acrosome reaction (AR) and fertilize oocytes. Although the molecular mechanisms of capacitation are not completely elucidated, many studies have demonstrated an involvement of numerous structural and biochemical modifications in spermatozoa, such as changes in membrane composition and fluidity [4][5][6], increased intracellular calcium [7][8][9], cytoplasmic alkalinization [10,11], activation of ion channels [12,13], and generation of reactive oxygen species [14,, 15]. Capacitation is associated with protein tyrosine phosphorylation [8,[16][17][18], which is modulated via a cAMPdependent pathway in many species, including the mouse, human, and bull [8, 19,, 20].…”