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 drk1 channel (with the first 139 amino acids of the N terminus delected, Ndrk1) caused a voltage-independent elevation of current amplitude, which was not seen for endogenous currents or for wild-type full-length drk1 channel. This effect on Ndrk1 was blocked by pre-injection of oocytes with Walsh-peptide protein kinase A inhibitor, suggesting mediation via protein kinase A. The protein kinase inhibitor also reduced both Ndrk1 and full-length drk1 currents. Substitution of the serine residues by alanine at one or both of the two consensus protein kinase A phosphorylation sites on the C terminus (residues 440 and 492) of Ndrk1 resulted in a loss of function of the expressed channels. These results indicate that phosphorylation via protein kinase A modulates drk1 channel function and that both consensus phosphorylation sites seems to be essential for channels to function.