MODULATION BY PROTEIN-KINASE-A OF A CLONED RAT-BRAIN POTASSIUM CHANNEL EXPRESSED IN XENOPUS-OOCYTES

A potassium channel from rat brain was expressed in Xenopus oocytes in order to study modulation of channel function by phosphorylation via protein kinase A. Application of 8-Br-cAMP to oocytes expressing the d rk1 channel (with the first 139 amino acids of the N terminus delected , Delta Ndrk1) caused a voltage-independent elevation of current ampli tude, which was not seen for endogenous currents or for wild-type full -length drk1 channel. This effect on Delta Ndrk1 was blocked by pre-in jection of oocytes with Walsh-peptide protein kinase A inhibitor, sugg esting mediation via protein kinase A. The protein kinase inhibitor al so reduced both Delta Ndrk1 and full-length drk1 currents. Substitutio n of the serine residues by alanine at one or both of the two consensu s protein kinase A phosphorylation sites on the C terminus (residues 4 40 and 492) of Delta Ndrk1 resulted in a loss of function of the expre ssed channels. These results indicate that phosphorylation via protein kinase A modulates drk1 channel function and that both consensus phos phorylation sites seems to be essential for channels to function.