TI - An amino acid mutation in a potassium channel that prevents inhibition by protein kinase C . AB - A slowly activating , voltage -dependent potassium channel protein cloned from rat kidney was expressed in Xenopus oocytes . Two activators of protein kinase C , 1-oleoyl-2-acetyl-rac-glycerol and phorbol 12, 13-didecanoate , inhibited the current . This inhibition was blocked by the kinase inhibitor staurosporine . Inhibition of the current was not seen in channels in which Ser103 was replaced by Ala , although other properties of the current were unchanged . These results indicate that inhibition of the potassium current results from direct phosphorylation of the channel subunit protein at Ser103 .