Membrane potential gradient is carbon monoxide-dependent in mouse and human small intestine

The aims of this study were to quantify the change in resting membrane potential (RMP) across the thickness of the circular muscle layer in the mouse and human small intestine and to determine whether the gradient in RMP is dependent on the endogenous production of carbon monoxide (CO). Conventional sharp glass microelectrodes were used to record the RMPs of circular smooth muscle cells at different depths in the human small intestine and in wild-type, HO2-KO, and W/W(V) mutant mouse small intestine. In the wild-type mouse and human intestine, the RMP of circular smooth muscle cells near the myenteric plexus was -65.3 +/- 2 mV and -58.4 +/- 2 mV, respectively, and -60.1 +/- 2 mV and -49.1 +/- 1 mV, respectively, in circular smooth muscle cells at the submucosal border. Oxyhemoglobin (20 microM), a trapping agent for CO, and chromium mesoporphyrin IX, an inhibitor of heme oxygenase, abolished the transwall gradient. The RMP gradients in mouse and human small intestine were not altered by N(G)-nitro-l-arginine (200 microM). No transwall RMP gradient was found in HO2-KO mice and W/W(V) mutant mice. TTX (1 microM) and 1H-[1,2,4-]oxadiazolo[4,3-a]quinoxalin-1-one (10 microM) had no effect on the RMP gradient. These data suggest that the gradient in RMP across the thickness of the circular muscle layer of mouse and human small intestine is CO dependent.