GALANIN INDUCES OPPOSITE EFFECTS VIA DIFFERENT INTRACELLULAR PATHWAYSIN SMOOTH-MUSCLE CELLS FROM DOG COLON

Smooth muscle cells isolated by enzymatic digestion were used to deter mine the direct effects of galanin on circular and longitudinal muscle layers from dog proximal colon and to investigate the intracellular p athways involved in these effects. Effects of galanin were compared to those observed with other contracting [cholecystokinin octapeptide (C CK8)] and relaxing [vasoactive intestinal peptide (VIP)] agents. In lo ngitudinal cells, galanin and CCK8 induced a contraction that was maxi mal at 1 nM galanin and 1 nM CCK8 and was 23.9 +/- 4.5% and 23.4 +/- 3 .4%, respectively, of the length of resting cells. Incubation of cells in Ca2+-free medium or in the presence of nifedipine caused an inhibi tion of galanin-induced contraction whereas it had no effect on the co ntraction induced by CCK8. Vasoactive intestinal peptide, forskolin, a nd 8 bromo cAMP inhibited CCK-induced contraction but failed to inhibi t contraction induced by galanin. The contraction induced by galanin w as abolished the CCK-indueed contraction was unchanged by pertussis to xin. In circular cells, CCK8 induced a contraction that was maximal at 10 nM and was 24.2 +/- 2.6%. Galanin had no effect by itself. When ce lls were preincubated (1 min) with galanin (10 fM-1 mu M), the CCK8-in duced contraction was inhibited, with a maximal effect at 10 nM galani n. Likewise, VIP inhibited the CCK8-induced contraction with a maximal effect at 1 mu M. Preincubation of cells with somatostatin, N-ethylma leimide, and (R)-p-cAMPS inhibited galanin- and VIP-induced relaxation . In conclusion, galanin induces a contraction of longitudinal smooth muscle cells that is dependent on an influx of extracellular calcium a nd an activation of a pertussis toxin G-protein. Galanin induces a rel axation of circular smooth muscle cells by activation of the adenylate cyclase complex and protein kinase A.