Sources of activator Ca2+ for galanin-induced contractions of rat gastric fundus, jejunum and colon

Galanin (Gal) evoked reproducible contractions of isolated rat gastric fundus, colon and jejunum longitudinal strips in concentrations ranging from 1 nM to 3 muM EC50 of Gal equalled 12.63, 23.27 and 56.02 nM, respectively. Hill's coefficients were not different from unity in any of the tissues examined. Experiments have been performed in the presence of protease and peptidase inhibitors, a variety of specific antagonists and tetrodotoxin (TTX) to exclude the non-specific stimulatory or inhibitory action of Gal. Gal-evoked contractions were attenuated by diminished extracellular Ca2+ concentration and by diltiazem. Gal activity in gastric fundus and colon, but not in jejunum was inhibited by depleting intracellular Ca2+ stores, thapsigargin, dantrolene, ryanodine, TMB-8, neomycin and U-73122. Our data confirmed that Gal contracts rat fundus, jejunum and colon by stimulating specific receptors, which are coupled both to Ca2+ influx through the voltage-dependent calcium channels and intracellular Ca2+ release from ryanodine- and IP3-sensitive stores (stomach and colon) or the extracellular Ca influx only (jejunum). Phosphatidylinositol-specific phospholipase C (PI-PLC) plays a crucial role in the former but not in the latter signal transduction cascade.