Activation of protein kinase C sensitizes human VR1 to capsaicin and to moderate decreases in pH at physiological temperatures in Xenopus oocytes

The two-electrode voltage-clamp technique was used to evaluate the effect of protein kinase C (PKC) activation on ion current flow in Xenopus laevis oocytes injected with cRNA coding for the human vanilloid receptor (VR1). In the presence of 30 nM phorbol-12,13-dibutyrate (PDBu), current evoked by an effective concentration (EC30) of capsaicin (CAP) was potentiated by 638 +/- 117% (n = 8). PDBu exhibited an EC50 of about 17+/-3 nM for this effect (n = 8). Potentiation was not observed when VR1 expressing oocytes were exposed to both 30 nM PDBu and 1 muM staurosporine. In the presence of 300 nM PDBu, the EC50 for CAP shifted from 899+/-78 to 139+/-2 1 nM (n = 11 and 5, respectively). In the presence of 30 nM PDBu, the maximal current amplitude evoked by application of CAP increased by 86+/-21% (n = 10), in a staurosporine sensitive manner. Application of 1 muM PDBu alone elicited a capsazepine sensitive current within 3 min of exposure. This effect was observed in the absence of previous exposure of the oocyte to CAP and was abolished in the presence of 1 muM staurosporine. No current was elicited during a 10 min application of 300 nM PDBu, the longest interval assessed. Prior to 30 nM PDBu exposure, no current was evoked at temperature ramps from room temperature (22-23degreesC) up to 37degreesC at pH 6.8, 7.0, or 7.4. Following PDBu treatment, VR1 mediated current was evoked at 26degreesC at pH 7.0. Likewise, following 30 nM PDBu treatment, current was evoked by application of pH 6.8 alone and a further increase in current amplitude was evoked by heat at 24degreesC in a staurosporine sensitive manner. These data provide direct evidence that PKC activation can increase VR1 current evoked by candidate physiological activators, pH and heat. This observation provides an empirical foundation for explaining some types of inflammatory pain in terms of PKC activation, small decreases in tissue pH levels, and small increases in skin temperature, all of which can accompany inflammatory conditions. (C) 2002 Published by Elsevier Science B.V. on behalf of International Association for the Study of Pain.