Nasu, Y. and Sakamoto, Y. Mechanisms of the depolarization and contracture due to Na removal in the circular muscle of the guinea-pig stomach. Jpn. J. Smooth Muscle Res., 26 (4), 191-198, 1991 Verapamil (10^-6 M) significantly reduced a development of the membrane depolarization and the contracture which were induced by Na removal. The fully developed depolarization, after exposure to Na-free solution, was reduced greatly by verapamil, excess Ca (15 mM) or sodium nitroprusside (10^-6 M), but some depolarization still remained. This remaining depolarization was completely blocked by readmission of 10 mM Na to Na-free solution containing verapamil, excess Ca or sodium nitroprusside. However, Mn (1.5 mM) did not block the depolarization due to Na removal and if Mn was present in Na-free solution, readmission of 15 mM Na to Na-free solution was not able to block the depolarization. On the other hand, the contracture due to Na removal was inhibited by addition of Mn (1.5 mM) or sodium nitroprusside (10^-6 M), but partially by addition of verapamil (10^-6 M) or excess Ca, to Na-free solution. These remaining contractures were also abolished by readmission of 10 mM Na to Na-free solution containing verapamil or excess Ca.
Thus, these results suggest that the depolarization and the contracture due to Na removal are induced by increase in cytoplasmic Ca concentrations through (1): verapamil-sensitive Ca channel, (2): Na-Ca exchange system and (3): some mechanism which is inhibited by sodium nitroprusside.

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esponses of isolated muscle strips from the rat and the dog internal anal sphincter (IAS) to drugs and electrical field stimulation (EFS) were investigated in vitro for the purpose of clarifyng a manner of neural control of IAS. Also, responses of muscle strips from IAS of the patients with Hirschsprung's disease were compared with those of muscle strips from human control IAS. Muscle strips from the dog and human IAS as normal control showed contractions to norepinephrine (NE), which were abolished in the presence of phentolamine and relaxations to isoproterenol. EFS (<1 msec) induced relaxations of the muscle strips. These responses to EFS were not affected by either one of phentolamine, propranolol and atropine but were inhibited by tetrodotoxin. Muscle strips from IAS in Hirschsprung's disease contracted to both NE and EFS, the responses of which were abolished in the presence of phentolamine. But no relaxation to EFS of muscle strips from IAS in Hirschsprung's disease was observed.
These findings revealed that normal IAS is pharmacologically innervated by α-adrener-gic excitatory nerve, β-adrenergic inhibitory nerve and non-adrenergic, non-cholinergic inhibitory nerve and suggested that IAS in Hirschsprung's disease is also affected by α-adrenergic excitatory nerve but inhibitory neural control is abscent.

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Cutaneous recording of electrogastrography reflects gastric mechanical activity. Epigastric leads are superior in recording characteristics than mesogastric leads, in fasting state. 3.0 cpm waves dominate EGG recording in fasting state. In this study, we analyzed the EGG recording characteristic after feeding in 10 normal subjects. Though the physical changes of gastric shape and volume after feeding, EGG recording was dominated by 3.0 cpm waves. Epigastric leads are still superior in recording characteristics, amplitude of EGG waves and readabilities, than mesogastric leads, after feeding. Amplitude of EGG waves increased after feeding when compared to fasting state, suggesting increased mechanical activity of the stomach. We conclude that epigastric leads are suitable in recording of EGG in fasting and in fed state in normal subjects. This position could be most standard recording leads for EGG in clinical settings.

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