Voltage and receptor mediated contractile activity of colonic smooth muscle in calcium-free solution.

Normal mechanical activity of cat colonic muscle segments was abolished during incubation in calcium-free solution. In calcium-free solution, contractions could be induced by direct electrical stimulation or by depolarization with high potassium. In high potassium calcium-free solution, carbachol also induced an additional contractile response due to muscarinic receptor occupation. It is concluded that in colonic smooth muscle, depolarization mediated, as well as receptor mediated, release of intracellular calcium occurs.