Effect of Ethanol on Spontaneous Phasic Contractions of Cat Gastric Smooth Muscle

Background: Ethanol is generally believed to inhibit extracellular Ca 2+ influx, thereby inhibiting gastric muscle contraction. Recently, we observed that verapamil inhibited only the amplitude of spontaneous phasic contractions, whereas ethanol inhibited both amplitude and frequency. In our objective to investigate the mechanism of ethanol's inhibition of gastric motility, the involvement of various protein kinases in ethanol-inhibited spontaneous phasic contractions of the stomach muscle strips was tested. Methods: Circular muscle strips (2.0 × 0.2 cm) were prepared from the corpus of cat stomach in order to measure isometric contraction in a chamber filled with Krebs-Ringer solution (pH 7.4, temperature 36 °C) bubbled with 5% CO 2 in O 2. Results: Spontaneous phasic contraction was not affected by various receptor antagonists (1 μM atropine, 1 μM hexamethonium, 1 μM phentolamine and 1 μM propranolol) or 1 μM tetrodotoxin. EGTA and verapamil dose-dependently inhibited only the amplitude of spontaneous phasic contractions and not the frequency. Ethanol dose-dependently inhibited both the amplitude and frequency of phasic contractions. The amplitude and frequency of spontaneous phasic contractions were significantly inhibited by protein kinase C and tyrosine kinase inhibitors. However, neither protein kinase C activator nor various phosphatase inhibitors blocked the inhibitory effect of ethanol. Conclusions: Ethanol appears to inhibit spontaneous phasic contractions by a mechanism other than the inhibition of protein kinase C or tyrosine kinase or the inhibition of extracellular Ca 2+ influx.