Cholinergic regulation of Na+-K+-ATPase activity in rat parotid gland: changes after castration

In this study, we investigated the different signalling pathways involved in muscarinic acetylcholine M(3) receptor-dependent modulation of Na(+)-K(+)-ATPase in parotid glands from normal and castrated rats. Carbachol inhibited the enzyme activity in parotid glands from control rats while it stimulated the enzyme activity in castrated rats. The inhibition of Ca(2+) calmodulin by trifluoperazine abolished the inhibitory effect of carbachol in control rats, while the inhibition of protein kinase C by staurosporine stimulated Na(+)-K(+)-ATPase. In castrated rats, trifluoperazine inhibited the carbachol-stimulant effect while staurosporine had no effect. Results indicate that in control glands the activation of a phospholipid-Ca(2+) calmodulin-dependent protein kinase C is responsible for the inhibitory effect of carbachol on Na(+)-K(+)-ATPase activity. In castrated rats, the activation of the enzyme by carbachol is regulated by its Ca(2+) calmodulin-stimulating action, and not by activation of protein kinase C. The activation of the Na(+)-K(+)-ATPase observed in castrated rats resulted in a decrease in carbachol-induced net K(+) efflux and thereby could decrease salivary fluid production.