Initial evidence for the modification of hamster sperm Na⁺, K⁺-ATPase activity by cyclic nucleotide-mediated processes

Na⁺, K⁺-ATPase activity of homogenates prepared from cauda epididymal golden hamster sperm increased after the addition of cGMP (50μM), monobutyryl cGMP (0.5μM) or cGMP-dependent protein kinase (0.94μg/ml). Addition of monobutyryl cAMP (0.5μM) or purified catalytic subunit of cAMP-dependent protein kinase (1.26μg/ml) inhibited the activity of the Na⁺, K⁺-ATPase. Preincubation with a partially purified preparation of cAMP-dependent protein kinase inhibitor (75μg/ml) stimulated the activity of the Na⁺, K⁺-ATPase, and this stimulation was decreased by the addition of 5μM monobutyryl cAMP. It is not yet known whether direct and/or indirect mechanisms are involved, but these results are the first to describe such opposing effects by cyclic nucleotide-mediated processes on a Na⁺, K⁺-ATPase activity.