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

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Abstract
1 Whole-cell voltage-clamp techniques were used to investigate the capsaicin-, 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 μm) to HEK 293 cells expressing the rVR1 receptor led to the appearance of inward currents (EC50, 497 nm; Hill coefficient, nH, 2.85) which were reversibly antagonized by 10 μm capsazepine. 3 Current-voltage relationships, determined using depolarizing or hyperpolarizing voltage ramps, had reversal potentials close to 0 mV, exhibited substantial outward rectification and possessed a region of negative slope conductance at holding potentials negative to around −70 mV. Further experiments indicated that the outward rectification and the region of negative slope conductance did not result from external block of the channel by either Ba2+, Ca2+ or Mg2+. 4 During our characterization of rVR1, it became apparent that the rectification behaviour of this receptor was not entirely instantaneous as might be expected for a ligand-gated ion channel, but rather displayed clear time-dependent components. We characterized the kinetics of these novel gating properties 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 developed with mean time constants of 6.7 ± 0.7 and 51.8 ± 18.4 ms, with the faster time constant playing a dominant role (64.4 ± 3.8%). Similar kinetics also described the decay of ‘tail currents’ observed on repolarization. Furthermore, these time-dependent changes appeared to be unaffected by the removal of extracellular divalent cations and were not significantly voltage dependent. 6 Our data reveal that rVR1 exhibits substantial time- and voltage-dependent gating properties that may have significance for the physiology of sensory transduction of nociceptive signals.