INHIBITORY-ACTION OF ACETYLCHOLINE, BACLOFEN AND GTP-GAMMA-S ON CALCIUM CHANNELS IN ADULT-RAT SENSORY NEURONS

High- and low-voltage activated calcium channel currents (HVA and LVA) were inhibited by acetylcholine (10-100-mu-M) and baclofen (10-mu-M) in adult rat sensory neurons. This modulatory effect was present on dihydropyridine (nifedipine 1-mu-M) and/or omega-conotoxin (3.2-mu-M, 2-5 h incubation) insensitive components and was insensitive to holding potentials (V(h) -50 to -90 mV). GTP-gamma-S (100-mu-M) prolonged calcium channel current activation in a time- and voltage-dependent manner. On the other hand, the current amplitude reduction induced by muscarinic and GABA(B) receptor activation, was not relieved by a 50-ms conditioning prepulse to +50 mV. This suggests the possibility of an alternative voltage-independent modulation mechanism.