Effects of acclimation temperatures of 7 and 14 degrees C on the contractility of Atlantic salmon (Salmo salar) intestinal smooth muscle in vitro

The contractility of intestinal smooth muscle of Atlantic salmon (Salmo salar) acclimatized to temperatures of 7 and 14 degrees C was compared over a prolonged period of time (9 months) in freshwater. Initial studies were carried out on intestine isolated from Atlantic salmon to estimate optimal conditions for contractility. Subsequent studies were carried out with the neurotransmitter/agonist 5-HT and TS, which activates neuronal elements in the intestine, in a Krebs-Henseleit solution containing HEPES buffer maintained at pH 7.85 and at the temperature of the experimental group (i.e., 7 or 14 degrees C). There was a significant interaction with time and temperature for the maximal response of 5-HT (p=0.005), effective concentration producing 50% of the maximal response (EC50) to 5-HT (p=0.026) and maximal response to TS (p=0.002), demonstrating that gastrointestinal contractility of Atlantic salmon is altered by both time (month) and temperature. No significant changes were found with the effective frequency producing 50% of the maximal response (EF50) to TS. The potency (EC50 of 5-HT) increase between 7 and 14 degrees C was statistically significant (p=0.026) but the small differences found with potency were most likely not physiologically significant. A time shift was recognized in the maximal responses to 5-HT, by applying a time variable to equations for the curves of the responses. This demonstrated that the curves are similar for both temperatures but alterations in the time of the maximal response changes was different. Thus, there is a delay in the time (month) changes of gastrointestinal contractility related to acclimation temperature and would be an area for future study.