Native Kv1.3 channels are upregulated by protein kinase C

The voltage-gated potassium channel, Kv1.3, which is highly expressed in a number of immune cells, contains concensus sites for phosphorylation by protein kinase C (PKC). In lymphocytes, this channel is involved in proliferation-through effects on membrane potential, Ca2+ signalling, and interleukin-2 secretion-and in cytotoxic killing and volume regulation. Because PKC activation (as well as increased intracellular Ca2+) is required for T-cell proliferation, we have studied the regulation of Kv1.3 current by PKC in normal (nontransformed) human T lymphocytes. Adding intracellular ATP to support phosphorylation, shifted the voltage dependence of activation by +8 mV and inactivation by +17 mV, resulting in a 230% increase in the window current. Inhibiting ATP production and action with "death brew" (2-deoxyglucose, adenylylimidodiphosphate, carbonyl cyanide-m-chlorophenyl hydrazone) reduced the K+ conductance (GK) by 41 +/- 2%. PKC activation by 4 beta-phorbol 12,13-dibutyrate, increased GK by 69 +/- 6%, and caused a positive shift in activation (+9 mV) and inactivation (+9 mV), which resulted in a 270% increase in window current. Conversely, several PKC inhibitors reduced the current. Diffusion into the cell of inhibitory pseudosubstrate or substrate peptides reduced GK by 43 +/- 5% and 38 +/- 8%, respectively. The specific PKC inhibitor, calphostin C, potently inhibited Kv1.3 current in a dose- and light-dependent manner (IC50 approximately 250 nM). We conclude that phosphorylation by PKC upregulates Kv1.3 channel activity in human lymphocytes and, as a result of shifts in voltage dependence, this enhancement is especially prevalent at physiologically relevant membrane potentials. This increased Kv1.3 current may help maintain a negative membrane potential and a high driving force for Ca2+ entry in the presence of activating stimuli.