Hamster sperm Na+, K+-adenosine triphosphatase: increased activity during capacitation in vitro and its relationship to cyclic nucleotides

These in vitro studies of golden hamster sperm were undertaken to determine whether: Na+, K+adenosine triphosphatase (ATPase) activity is required for capacitation; Na+, K4’-ATPase activity is altered during capacitation; and cyclic nucleotides can control this enzyme activity, Hamster sperm were incubated in a medium in which capacitation occurred in an asynchronous manner and in which acrosome reactions began to occur after approximately 3.5 h of incubation. Inhibition of the hamster sperm acrosome reaction by the Na”, K”ATPase inhibitor ouabain (1 MM) added at Time (T)=2 or T=3 h could be fully reversed by the addition of the ionophore nigericin (0,1 MM) at T=3.5 h. However, when ouabain was added at T=0 or T=1 h, similar nigericin addition could not completely reverse the inhibition. Na+, K+ATPase activity of hamster sperm increased by 2 h of incubation (compared to that measured initially after 15 mm) and this activity remained elevated at 3.5 h. Addition of either monobutyryl cyclic adenosine 3’:5’-monophosphate (BtcAMP) (12.9 MM)or monobutyryl cyclic guanosine monophosphate (BtcGMP) (10.5 MM), or the phosphodiesterase inhibitor SQ20009 (10 MM) at 2 h produced a stimulation of acrosome reactions at 4 and 5 h. However, while BtcGMP and SQ 20009 also induced a further increase in Na, K’-ATPase activity measured at 3.5 h, BtcAMP had no effect. Intracellular cAMP and cGMP levels measured showed cAMP increased by 2 h and remained elevated when measured at 3.5 h, while cGMP could not be consistently detected at 15 mm, 2 h or 3.5 h, However, assays of high numbers of uncapacitated sperm did detect a low level of cGMP. These results suggest that Na’1’, K’1.ATPase activity increases in and is essential for early capacitation Land thereby eventually for the acrosome reaction (AR) I of hamster sperm and that the increase in Na+, K’1’-ATPase activity occurring during capacitation is probably mediated by intracellular cGMP but not cAMP, although both cyclic nucleotides stimulate the hamster sperm AR