Ca2+ -activated K+ conductance in internally perfused snail neurons is enhanced by protein phosphorylation.

Depolarizing voltage steps induce inward and outward currents in voltage-clamped, internally perfused neurons from the snail Helix roseneri. Addition of the catalytic subunit of cyclic AMP-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37) to the internal perfusing medium results in an increase in the net outward current, with no apparent effect on the inward current. Catalytic subunit inactivated by 5,5'-dithiobis(2-nitrobenzoic acid) is without effect, indicating that the increase in net outward current results from protein phosphorylation rather than an unspecific effect of protein perfusion. Decreasing the external Ca2+ concentration from 10 to 1 mM eliminates the effect of catalytic subunit, suggesting that Ca2+ plays an important role in this response. This suggestion is supported by the fact that the stimulation by catalytic subunit can be mimicked by increasing the Ca2+ concentration in the internal perfusion medium and can be prevented by intracellular perfusion with 10 mM EGTA. The results are consistent with the hypothesis that cyclic AMP-dependent protein phosphorylation regulates the Ca2+-activated K+ conductance in these cells.