Complexity of the regulation of Kir2.1 K+ channels.

Regulation of native inward-rectifier K+ channels by second-messenger systems is important for the control of membrane potential and excitability in various types of cell. Regulation of cloned IRK1 (Kir2.1) channels was investigated in inside-out patches from Xenopus oocytes. Fast run down of Kir2.1 channels was induced by application of GTP-gamma S to the cytoplasmic side of the patches and reversed by application of PKA plus Mg-ATP. This effect of GTP-gamma S was inhibited by the phosphatase inhibitor microcystin. These results suggest regulation of Kir2.1 channels by a G-protein-controlled phosphatase. A similar effect was observed upon application of G-protein beta gamma subunits. This effect, however, was most likely mediated by contamination of this preparation by the antioxidant DTT, since DTT by itself was also able to induce a fast run-down of Kir2.1 channels. On the other hand, DTT was found to reverse the run-down induced by GTP-gamma S, similar to PKA. This results indicate that DTT mediates two opposite effects on Kir2.1 channels. It is concluded that regulation of Kir2.1 channels is complex and most likely involves other proteins endogenously expressed in Xenopus oocytes, such as ABC-proteins, G-proteins and phosphatases, which are sensitive to oxidation.