Regulation of native Kv1.3 channels by cAMP-dependent protein phosphorylation.
We present evidence that activity of native Kv1.3 channels in human T lymphocytes can be increased by inhibiting phosphatases [using okadaic acid (OA)] or by activating protein kinase A (PKA). OA increased the maximal conductance (Gmax) by 40% and shifted the voltage dependence of activation and inactivation, resulting in a significant increase in window current around the normal membrane potential. PKA inhibition [using the PKA inhibitor peptide PKI-(5-24)] decreased Gmax by 43%, whereas PKA activation [by the Sp diastereomer of adenosine 3',5'-cyclic monophosphothioate (Sp-cAMPS)] increased Gmax by 60% and shifted the inactivation curve, producing an increase in the window current. These results are consistent with our previously published work using cell-attached patches but differ from some studies of Kv1.3. Because we previously reported a similar upregulation by protein kinase C (PKC) activation in these cells, we tested whether the PKA and PKC effects were additive. Our results suggest that PKC-dependent phosphorylation acts as a master switch, inasmuch as calphostin C greatly inhibited the current even after Sp-cAMPS, OA, or PKC activation was used to increase protein phosphorylation. Inasmuch as phosphorylation by both kinases (phorbol ester followed by Sp-cAMPS) abrogated the effects of either kinase alone, our results support the view that Kv1.3 is regulated in a complex manner by serine/threonine phosphorylation.
Chung
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Playfair Neuroscience Unit, Toronto Hospital Research Institute, Ontario, Canada.
Schlichter
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D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism / Q000502:physiology; D004553:Electric Conductivity; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D051664:Kv1.3 Potassium Channel; D019319:Okadaic Acid / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D011188:Potassium / Q000502:physiology; D015221:Potassium Channels / Q000378:metabolism* / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D011493:Protein Kinase C / Q000502:physiology; D013601:T-Lymphocytes / Q000378:metabolism
D004791:Enzyme Inhibitors; C496973:KCNA3 protein, human; D051664:Kv1.3 Potassium Channel; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D019319:Okadaic Acid; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010744:Phosphoric Monoester Hydrolases; D011188:Potassium