RESUMO
BACKGROUND: The contraction of smooth muscle depends on an increase in the concentration of intracellular calcium ion and the source of this increase to various stimuli is different according to organs or species. Nevertheless, there have been only a few studies on human stomach smooth muscle. This study was designed to identify the source of the calcium utilized in the muscle contraction induced by carbachol, which is an important factor among various stimuli. METHODS: After the administration of carbachol with various conditions in cultured human stomach smooth muscle cells, fura-2-acetoxymethyl ester was used to measure the increase in the intracellular calcium concentration. RESULTS: (1) The carbachol-induced increase in the intracellular calcium concentration was not attenuated after removal of extracellular calcium. (2) Carbachol induced a small increase in the intracellular calcium concentration even after the depletion of intracellular calcium store. (3) Repeated histamine administration blocked the carbachol-induced increase in the intracellular calcium concentration in calcium-free extracellular solution. CONCLUSION: The main source of calcium utilized in human stomach smooth muscle contraction by carbachol is intracellular calcium store, particularly inositol triphosphate(IP3)-sensitive calcium stores. However, extracellular calcium also contributes to the carbachol-induced increase in the intracellular calcium concentration.