Galanin inhibition of voltage-dependent Ca²⁺ influx in rat cultured myenteric neurons is mediated by galanin receptor 1

Galanin activates three receptors, the galanin receptor 1 (GalR1), GalR2, and GalR3. In the gastrointestinal tract, GalR1 mediates the galanin inhibition of cholinergic transmission to the longitudinal muscle and reduction of peristalsis efficiency in the small intestine. Galanin has also been shown to inhibit depolarizationevoked Ca²⁺ increases in cultured myenteric neurons. Because GalR1 immunoreactivity is localized to cholinergic myenteric neurons, we hypothesized that this inhibitory action of galanin on myenteric neurons is mediated by GalR1. We investigated the effect of galanin 1-16, which has high affinity for GalR1 and GalR2, in the presence or absence of the selective GalR1 antagonist, RWJ-57408, and of galanin 2-11, which has high affinity for GalR2 and GalR3, on Ca²⁺ influx through voltage-dependent Ca²⁺ channels in cultured myenteric neurons. Myenteric neurons were loaded with fluo-4 and depolarized by high K⁺ concentration to activate voltage-dependent Ca²⁺ channels. Intracellular Ca²⁺ levels were quantified with confocal microscopy. Galanin 1-16 (0.01-1 μM) inhibited the depolarization- evoked Ca²⁺ increase in a dose-dependent manner with an EC50 of 0.172 μM. The selective GalR1 antagonist, RWJ-57408 (10 μM), blocked the galanin 1-16 (1 μM)-mediated inhibition of voltage-dependent Ca²⁺ channel. By contrast, the GalR2/GalR3 agonist, galanin 2-11 did not affect the K⁺-evoked Ca²⁺ influx in myenteric neurons. GalR1 immunoreactivity was localized solely to myenteric neurons in culture, as previously observed in intact tissue. These findings indicate that the inhibition of depolarization-evoked Ca²⁺ influx in myenteric neurons in culture is mediated by GalR1 and confirm the presence of functional GalR1 in the myenteric plexus. This is consonant with the hypothesis that GalR1 mediates galanin inhibition of transmitter release from myenteric neurons.