Cooling-induced contraction in ileal longitudinal smooth muscle of guinea-pig

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Abstract
The ileal longitudinal smooth muscle developed a transient contraction on cooling from 37 °C to 1 °C in normal Ca2+ (2.5 mm) medium. The transient contraction was not inhibited by pretreatment with the Ca2+ antagonist, D−600 (1 times 10−6 m). The contractions were sustained by cooling to 1 °C in the presence of added Ca2+ greater than 10 mm. After the pretreatment with D−600, when the muscle incubated in normal medium with added 20 mm Ca2+ had been cooled to 1 °C, a phasic response was only seen. However, D−600 did not inhibit the sustained contraction at 1 °C after incubation in the presence of added 20 mm Ca2+. It is suggested that the transient and sustained contraction at 1 °C is maintained by Ca2+ release from a cellular site, probably the cell membrane and it requires more calcium for the sustained tension.