Capsazepine block of voltage-activated calcium channels in adult rat dorsal root ganglion neurones in culture

1 We have found that capsazepine antagonist at the vanilloid (capsaicin) receptor, blocks voltage-activated calcium currents in sensory neurones. 2 The block of calcium current was slow to develop with a half time of about one minute at 100 mu M and lasted for the duration of the experiment. The rate of block of calcium current was strongly concentration-dependent. 3 The EC50 for the blocking effect at 0 mV was 7.7+/-1.4 mu M after 6 min exposure to capsazepine. The EC50 at equilibrium was estimated to be 1.4+/-0.2 mu M. 4 The block of calcium current showed some voltage-dependence but there was no indication of any selectivity of action for a calcium channel subtype. The characteristics of the blocking action of capsazepine on the residual current of cells which were pretreated with either omega-conotoxin or nimodipine were similar to control. 5 The data suggest that capsazepine, in addition to its competitive antagonism of vanilloid receptors, has a non-specific blocking action on voltage-activated calcium channels which should be taken into account when interpreting the effects of this substance on intact preparations in vitro or in vivo.