Abstract
The influence of sodium was studied on hormone and guanine nucleotide-induced stimulation and inhibition of adenylate cyclase and on beta-adrenoceptor binding in various membrane systems. Sodium exerted almost identical effects on stimulation and inhibition of adenylate cyclase by various stimulatory and inhibitory hormones in all of the systems studied. The potencies of the hormones and of GTP to increase or to decrease the enzyme activity were reduced by sodium ions, without changing the maximal degree of adenylate cyclase stimulation or inhibition. Stimulation and inhibition of adenylate cyclase by the stable GTP analog, GTP gamma S, was affected in an identical manner by sodium, causing a retardation in the onset without a change in final stimulation or inhibition by the analog. Similar to the well-known reduction in alpha 2-adrenoceptor affinity for agonists, sodium also reduced the apparent affinity of beta-adrenoceptors for the agonist, isoproterenol. It is concluded that sodium exerts identical effects on Ns and Ni, inhibiting the activation process of these two coupling components of the adenylate cyclase.
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