Neuropeptide galanin inhibits omega-conotoxin GVIA-sensitive calcium channels in parasympathetic neurons.

1. We determined the effect of the neuropeptide galanin on barium currents (IBa) flowing through voltage-gated calcium channels. We voltage clamped parasympathetic neurons dissociated from mudpuppy cardiac ganglia using both the standard whole cell and the perforated-patch variations of the patch-clamp technique. 2. Galanin produced a concentration-dependent inhibition of IBa. The maximal inhibition was 50-60% and the concentration that produced half-maximal inhibition (IC50) was 0.42 nM. In mud-puppy parasympathetic neurons, omega-conotoxin-GVIA (CTX)-sensitive channels are the predominant type of calcium channels, and only a small portion of IBa is contributed by dihydropyridine-sensitive channels. Galanin preferentially inhibited a portion of the CTX-sensitive current. 3. In currents recorded with the standard whole cell technique, activation of IBa was slowed in the presence of galanin. In contrast, in the majority of neurons studied with the perforated-patch technique, galanin decreased IBa without altering the kinetics of current activation. With both recording methods, the decrease in IBa was greatest with voltage steps to 0 mV and persisted with steps to +50 mV. For control currents, large depolarizing voltage steps (+70 to +120 mV) did not markedly facilitate IBa when either recording technique was used. However, the degree of facilitation in galanin was significantly greater with the standard whole cell recording technique. 4. IBa exhibited inactivation under the conditions of these experiments. Inactivation of IBa recorded during a 900-ms depolarizing voltage step was fitted to a double exponential. Galanin decreased the amplitude of IBa but did not alter the time constants of inactivation.(ABSTRACT TRUNCATED AT 250 WORDS)