MODULATION BY PROTEIN-KINASE-C ACTIVATION OF RAT-BRAIN DELAYED-RECTIFIER K+ CHANNEL EXPRESSED IN XENOPUS OOCYTES

The modulation by protein kinase C (PKC) of the RCK1 K+ channel was in vestigated in Xenopus oocytes by integration of two-electrode voltage clamp, site-directed mutagenesis and SDS-PAGE analysis techniques, Upo n application of beta-phorbol 12-myristate 13-acetate (PMA) the curren t was inhibited by 50-90%. No changes in the voltage sensitivity of th e channel, changes in membrane surface area or selective elimination o f RCK1 protein from the plasma membrane could be detected, The inhibit ion was mimicked by 1-oleoyl-2-acetyl-rac-glycerol (GAG) but not by al pha PMA, and was blocked by staurosporine and calphostin C, Upon delet ion of most of the N-terminus a preceding enhancement of about 40% of the current was prominent in response to PKC activation, Its physiolog ical significance is discussed, The N-terminus deletion eliminated 50% of the inhibition, However, phosphorylation of none of the ten classi cal PKC phosphorylation sites on the channel molecule could account, b y itself or in combination with others, for the inhibition, Thus, our results show that PKC activation can modulate the channel conductance in a bimodal fashion, The N-terminus is involved in the inhibition, ho wever, not via its direct phosphorylation.