The aim of this study was to assess the effect of cooling on smooth muscle contraction in various parts of the gastrointestinal tract (esophagus, stomach, duodenum, jejunum and colon) and to investigate the basic mechanism underlying cooling-induced (CIC) tonic and rhythmic contractions. Recordings of isometric tension from smooth muscle strips of different parts of the rat gastrointestinal tract were performed using organ-bath techniques, and stepwise cooling was applied. Cooling was tested before and after the addition of various standard agents interfering with known neurogenic (autonomic blockers, tetrodotoxin, capsaicin) and myogenic mechanims of contraction (calcium channel blockers, Sarcoplasmatic and Ca2+-ATPase pump inhibitors). Step-wise cooling (37 degrees C to 5 degrees C) of all gastrointestinal smooth muscle preparations induced reproducible graded tonic contractions, inversely proportional to temperature. CIC was most pronounced in the jejunum. Cooling abolished rhythmic smooth muscle activity. CIC was not dependent on a neural mechanism nor the release of neurotransmitters, but linked to translocation of calcium. It was reduced by incubation in Ca2+-free solution. Blockage of the Ca2+-ATPase pump, which inhibits the extrusion of calcium, plays a significant role in the process and enhances CIC. Cooling of gastrointestinal smooth muscle preparations induces graded myogenic contractions inversely proportional to the temperature. The mechanism is not dependent on local nervous control but related to a temperature-sensitive process of calcium translocation.
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