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 microM) and baclofen (10 microM) in adult rat sensory neurons. This modulatory effect was present on dihydropyridine (nifedipine 1 microM) and/or omega-conotoxin (3.2 microM, 2-5 h incubation) insensitive components and was insensitive to holding potentials (Vh -50 to -90 mV). GTP-gamma-S (100 microM) prolonged calcium channel current activation in a time- and voltage-dependent manner. On the other hand, the current amplitude reduction induced by muscarinic and GABAB 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.