Modulation of calcium-currents by capsaicin in a subpopulation of sensory neurones of guinea pig.
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 microM 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 Ca2+ currents may be related to the specific action of CAP on peptidergic sensory neurones.
Petersen
M
M
Max-Planck-Institut für Physiologische, Bad Nauheim, Federal Republic of Germany.
Wagner
G
G
Pierau
F K
FK
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D002211:Capsaicin / Q000494:pharmacology*; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D008610:Menthol / Q000494:pharmacology; D009475:Neurons, Afferent / Q000187:drug effects*
D015220:Calcium Channels; D008610:Menthol; D002211:Capsaicin