Modulation of calcium-currents by capsaicin in a subpopulation of sensory neurones of guinea pig

Summary The action of capsaicin (CAP) on the total Ca²⁺ current was examined in internally perfused voltage-clamped dorsal root ganglion (DRG) neurones of guinea pigs. CAP changed the total Ca²⁺ current in about 50% of the investigated DRG neurones (CAP-sensitive neurones) in the following way: (I) a transient increase of the current amplitude at potentials between – 35 mV and about – 10 mV was accompanied by a shift of the current-voltage relation towards negative potentials by 5–8 mV; (II) the current inactivation was accelerated at potentials positive to about – 35 mV; and (III) the current activation of Ca²⁺ currents (time to peak values) was also accelerated. Separated low voltage-activated (T-type) currents at potentials negative to about – 35 mV were either not affected or reduced. It remains undecided whether CAP increases T-type currents in a particular potential range or activates an N-type current. External application of 50 M Ni²⁺ blocks the effect of CAP, but does not affect the acceleration of the high voltage-activated (L-type) current inactivation induced by menthol. This appears to exclude a CAP effect on L-type current inactivation. CAP sensitive and CAP insensitive neurones could be discriminated by their different Ca²⁺ currents: the former demonstrate both fast and slow inactivating currents while the latter have only L-type currents. The observed changes of fast-inactivating Cat²⁺ currents may be related to the specific action of CAP on peptidergic sensory neurones.Send offprint requests to M. Petersen