Modulation of olfactory bulb neuron potassium current by tyrosine phosphorylation

Insulin causes a suppression of whole-cell voltage-dependent outward current in cultured neurons from the rat olfactory bulb. This suppression is time-dependent; it is mimicked by application of Src tyrosine kinase inside the cell via the whole-cell patch electrode or by treatment of the olfactory bulb neurons with the tyrosine phosphatase inhibitor pervanadate. The C-type inactivation properties of the outward current in olfactory bulb neurons resemble those of the cloned Kv1.3 potassium channel. In addition, at picomolar concentrations at which it is specific for Kv1.3, the scorpion toxin margatoxin blocks most of the olfactory bulb neuron outward current. Immunocytochemical analysis demonstrates that Kv1.3 is prominent in the cultured olfactory bulb neurons. To identify specific amino acid residues that might be important for potassium current modulation, we examined the effects of pervanadate and insulin on wild-type and mutant Kv1.3 channels expressed in human embryonic kidney (HEK 293) cells. As shown previously, treatment with either pervanadate or insulin suppresses Kv1.3 current in these cells. Mutational analysis demonstrates that at least two distinct tyrosine residues are required for current suppression by pervanadate. Insulin treatment stimulates the tyrosine phosphorylation of Kv1.3 in HEK 293 cells, and a different combination of tyrosine residues is required for the current suppression by insulin. The results suggest that complex patterns of phosphorylation may be involved in the modulation of neuronal potassium current by receptor and nonreceptor tyrosine kinases.