Key result
Single colon circular smooth muscle cells generate spontaneous depolarizations similar to slow waves in intact tissues, requiring a temperature- and nickel-sensitive inward current.
Canine colon circular smooth muscle cells possess intrinsic pacemaker-like activity driven by specific inward currents.
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Does not yet alter clinical motility management; leaves open whether isolated cell pacemaking extends to human disease.
The type of cell that serves as the pacemaker in the colon is presently unknown. This study evaluated the ionic basis of spontaneous depolarizations in circular smooth muscle cells isolated from canine colon using whole cell voltage and current clamp techniques. Increasing temperature increased the probability of observing spontaneous depolarizations, depolarized the resting membrane potential (RMP), and increased Ca2+ and K+ currents. Spontaneous depolarizations occurred as rhythmic events, in bursts, or as isolated events. Varying the holding potential from -100 to -40 mV inhibited a component of inward current thought to be necessary for spontaneous depolarizations. The Ca2+ channel blockers, nickel and nisoldipine, inhibited spontaneous depolarizations. Nickel caused a hyperpolarization, whereas nisoldipine did not affect RMP. Ouabain depolarized the RMP and inhibited spontaneous depolarizations. The K+ channel blocker, tetraethylammonium, depolarized the RMP and lengthened the duration of spontaneous depolarizations. The key finding is that single colon circular smooth muscle cells are capable of generating spontaneous depolarizations similar to those described for slow waves in intact tissues and that a temperature- and nickel-sensitive inward current is essential for spontaneous activity.
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Post et al. (1992) studied this question. Ion channel blockers and temperature changes was evaluated on Spontaneous depolarizations. Single colon circular smooth muscle cells generate spontaneous depolarizations similar to slow waves in intact tissues, requiring a temperature- and nickel-sensitive inward current.
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