Voltage- and time-dependent properties of the recombinant rat vanilloid receptor (rVR1)

1. Whole-cell voltage-clamp techniques were used to investigate the capsaic in-, voltage- and time-dependent properties of the rat vanilloid receptor ( rVR1) stably expressed in human embryonic kidney (HEK) 293 cells. 2. At a holding potential of -70 mV, application of capsaicin (0.03-30 mu M ) to HEK 293 cells expressing the rVR1 receptor led to the appearance of in ward currents (EC50, 497 nM; Hill coefficient, n(H), 2.85) which were rever sibly antagonized by 10 mu M capsazepine. 3. Current-voltage relationships, determined using depolarizing or hyperpol arizing voltage ramps, had reversal potentials close to 0 mV, exhibited sub stantial outward rectification and possessed a region of negative slope con ductance at holding potentials negative to around -70 mV. Further experimen ts indicated that the outward rectification and the region of negative slop e conductance did not result from external block of the channel by either B a2+, Ca2+ or Mg2+. 4. During our characterization of rVR1, it became apparent that the rectifi cation behaviour of this receptor was not entirely instantaneous as might b e expected for a ligand-gated ion channel, but rather displayed clear time- dependent components. We characterized the kinetics of these novel gating p roperties in a series of additional voltage-step experiments. 5. The time-dependent changes in rVR1-mediated conductance due to membrane depolarization or repolarization occurred with bi-exponential kinetics. On depolarization to +70 mV the time-dependent increase in outward current dev eloped with mean time constants of 6.7 +/- 0.7 and 51.8 +/- 18.4 ms, with t he faster time constant playing a dominant role (64.4 +/- 3.8%). Similar ki netics also described the decay of 'tail currents' observed on repolarizati on. Furthermore, these time-dependent changes appeared to be unaffected by the removal of extracellular divalent cations and were not significantly vo ltage dependent. 6. Our data reveal that rVR1 exhibits substantial time- and voltage-depende nt gating properties that may have significance for the physiology of senso ry transduction of nociceptive signals.