Aerobic metabolism on muscle contraction in porcine gastric smooth muscle

Abstract

Exposure to chronic hypoxic conditions causes various gastric diseases, including gastric ulcers. It has been suggested that gastric smooth muscle contraction is associated with aerobic metabolism. However, there are no reports on the association between gastric smooth muscle contraction and aerobic metabolism, and we have investigated this association in the present study. High K⁺- and carbachol (CCh)-induced muscle contractions involved increasing O₂ consumption. Aeration with N₂ (hypoxia) and NaCN significantly decreased high K⁺- and CCh-induced muscle contraction and O₂ consumption. In addition, hypoxia and NaCN significantly decreased creatine phosphate (PCr) contents in the presence of high K⁺. Moreover, decrease in CCh-induced contraction and O₂ consumption was greater than that of high K⁺. Our results suggest that hypoxia and NaCN inhibit high K⁺- and CCh-induced contractions in gastric fundus smooth muscles by decreasing O₂ consumption and intracellular PCr content. However, the inhibition of CCh-induced muscle contraction was greater than that of high K⁺-induced muscle contraction.

Keywords: gastro intestine; hypoxia; smooth muscle.

Fig. 1.

Effects of applied NaCN (10 µM–1 mM) cumulatively on the H-65K⁺- and CCh-induced contraction in longitudinal and circular smooth muscle. A typical trace of longitudinal (A, B) and circular (C, D) smooth muscle contraction. E: Concentration–response association for NaCN-induced reduction obtained at the sustained phase of H-65K⁺ or CCh contraction. Each point represents the mean of 4 preparations. Vertical bars indicate S.E.M. * and ** indicate significant differences between H-65K⁺ and CCh in longitudinal muscle P<0.05 or at P<0.01 (n=4), respectively. † and †† indicate significant differences between H-65K⁺ and CCh in circular muscle at P<0.05 or P<0.01 (n=4–5), respectively. ‡ indicate significant differences between longitudinal and circular smooth muscle contraction induced by CCh (0.3 µM) at P<0.01 (n=4–5), respectively.

Fig. 2.

Effects of hypoxia (aerated 95% N₂, 5% CO₂) on the H-65K⁺- or CCh-induced contraction in longitudinal and circular smooth muscle. Typical trace of hypoxia-induced inhibition of H-65K⁺ (A)- or CCh (B)-induced contraction in longitudinal muscle. Values of aeration with N₂ instead of O₂ in presence of H-65K⁺ (C) and 0.3 µM CCh (D) were obtained 10 min after changing the aeration from O₂ to N₂. Values at 10 min were assigned as 100%. The data are expressed as means ± S.E.M. (n=4). ** Significantly different from the O₂ column (P<0.01).