The Journal of Neurophysiology Vol. 85 No. 1 January 2001, pp. 362-373
Copyright ©2001 by the American Physiological Society

Phorbol Ester-Induced Inhibition of Potassium Currents in Rat Sensory Neurons Requires Voltage-Dependent Entry of Calcium

 ¹Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120; and  ²Department of Physiology and Cell Biology/MS352, University of Nevada School of Medicine, Reno, Nevada 89557

Zhang, Yi-Hong, J. L. Kenyon, and G. D. Nicol. Phorbol Ester-Induced Inhibition of Potassium Currents in Rat Sensory Neurons Requires Voltage-Dependent Entry of Calcium. J. Neurophysiol. 85: 362-373, 2001. The whole cell patch-clamp technique was used to examine the effects of protein kinase C (PKC) activation (via the phorbol ester, phorbol 12,13 dibutyrate, PDBu) on the modulation of potassium currents (I_K) in cultured capsaicin-sensitive neurons isolated from dorsal root ganglia from embryonic rat pups and grown in culture. PDBu, in a concentration- and time-dependent manner, reduced I_K measured at +60 mV by ~30% if the holding potential (V_h) was 20 or 47 mV but had no effect if V_h was 80 mV. The PDBu-induced inhibition of I_K was blocked by pretreatment with the PKC inhibitor bisindolylmaleimide I and I_K was unaffected by 4- phorbol, indicating that the suppression of I_K was mediated by PKC. The inhibition of I_K by 100 nM PDBu at a V_h of 50 mV was reversed over several minutes if V_h was changed to 80 mV. In addition, intracellular perfusion with 5 mM bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) or pretreatment with -conotoxin GVIA or Cd²⁺-Ringer, but not nifedipine, prevented the PDBu-induced suppression of I_K at 50 mV, suggesting that a voltage-dependent influx of calcium through N-type calcium channels was necessary for the activation of PKC. The potassium channel blockers tetraethylammonium (TEA, 10 mM) and 4-aminopyridine (4-AP, 3 mM and 30 µM) reduced I_K, but only TEA attenuated the ability of PDBu to further inhibit the current, suggesting that the I_K modified by PDBu was sensitive to TEA. Interestingly, in the presence of 3 mM or 30 µM 4-AP, 100 nM PDBu inhibited I_K when V_h was 80 mV. Thus 4-AP promotes the capacity of PDBu to reduce I_K at 80 mV. We find that activation of PKC inhibits I_K in rat sensory neurons and that voltage-dependent calcium entry is necessary for the development and maintenance of this inhibition.