Excitation-Contraction Coupling in Canine Tracheal Smooth Muscle Cells

In canine tracheal smooth muscle, the significance of depolarization induced by acetylcholine is puzzling because it has no role in contraction. We proposed earlier a model where refilling of ACh-sensitive intracellular Ca2+ stores was in part achieved by a mechanism involving a direct influx of extracellular Ca2+ into the ACh-sensitive Ca2+ store through a dihydropyridine-sensitive channel. Putney proposed that different phases of the calcium response in non excitable cells may be intimately linked with IP3 first stimulating release of calcium from intracellular stores and the empty stores themselves then providing the signal that stimulates calcium entry. We examined in tracheal smooth muscle the essential feature of Putney’s model, that the intracellular stores themselves exert a major control over calcium entry.