Staurosporine directly blocks Kv1.3 channels expressed in Chinese hamster ovary cells

The effects of staurosporine (ST), a widely used protein kinase C (PKC) inh ibitor, were examined on Kv1.3 channels stably expressed in Chinese hamster ovary (CHO) cells using the whole-cell and excised inside-out configuratio ns of the patch clamp technique. In whole-cell recordings, ST, at external concentrations from 300 nM to 10 mu M, accelerated the rate of inactivation of Kv1.3 currents and thereby reduced the current at the end of the depola rizing pulse in a concentration-dependent manner with an IC50 of 1.2 mu M. The actions of ST were unaffected by pretreatment with another selective PK C inhibitor, chelerythrine, or by including the PKC pseudosubstrate peptide inhibitor, PKC 19-36, in the intracellular solution. Rp-cAMPS, a specific protein kinase A inhibitor, included in intracellular solution did not affe ct the effects of ST. Furthermore, the same effects of ST on Kv1.3 were als o observed in excised inside-out patches when applied to the internal face of the membrane. These effects were completely reversible upon washing. Cur rent-voltage relations for Kv1.3 currents at the end of voltage steps indic ated that ST reduced Kv1.3 currents over a wide voltage range. The blockade exhibited a shallow voltage dependence between -10 mV and +40 mV, increasi ng at more positive potentials. ST had no effect on the voltage dependence of steady-state inactivation. It reduced the tail current amplitude and slo wed the deactivation time course, resulting in a crossover phenomenon. Thes e results suggest that the action of ST on Kv1.3 is independent of PKC and PKA inhibition. ST blocks the open state of Ky 1.3 channels to produce an a pparent acceleration of the inactivation rate.