Acute suppression of inwardly rectifying Kir2.1 channels by direct tyrosine kinase phosphorylation.

Signaling via cytosolic and receptor tyrosine kinases is associated with cell growth and differentiation but also targets onto transmitter receptors and ion channels. Here, regulation by tyrosine kinase (TK) activity was investigated for inwardly rectifying K+ (Kir2.1) channels that control membrane excitability in many central neurons. In mammalian tsA-201 cells, the membrane-permeable protein tyrosine phosphatase inhibitor, perorthovanadate (100 microM), suppressed currents through recombinant Kir2.1 channels by 60 +/- 20%. Coapplication of the TK inhibitor genistein (100 microM) completely abolished this effect. Native Kir2.1 channels in rat basophilic leukocytes were affected by manipulation of the TK and protein tyrosine phosphatase activity in a qualitatively similar manner. Site mutation of a tyrosine consensus residue for TK phosphorylation in the C-terminal domain of Kir2.1 generated channel properties indistinguishable from wild-type Kir2.1 channels. However, Kir2.1Y242F channels were no longer suppressed following exposure to perorthovanadate, indicating that the channel is a direct substrate for TKs. After coexpression of nerve growth factor receptor with Kir2.1 channels in tsA-201 cells and Xenopus oocytes, the activity of Kir2.1 was rapidly suppressed by applied nerve growth factor (0.5 microgram/ml) by 31 +/- 10 and 21 +/- 15%, respectively. Acute inhibition was also evoked by epidermal growth factor and insulin via endogenous insulin receptors, indicating that Kir2.1 channels may serve as a general target for neurotrophic growth factors in the brain.