Electrical properties of colonic smooth muscle were investigated in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a model animal for spontaneous non-insulin-dependent diabetes mellitus (NIDDM), and the results were compared with those obtained from the Long-Evans Tokushima Otsuka (LETO) rat, a control of OLETF rat. At experiments (aged 60-80 weeks), blood glucose level was about 171 mg/dl in LETO rats and 370 mg/dl in OLETF rats. Feces in the colon were restricted to the proximal region in LETO rats and distributed widely in the whole colon in OLETF rats. In both LETO and OLETF rats, the circular smooth muscle strips of the isolated distal colon revealed two types of spontaneous electrical response, slow wave and transient hyperpolarization . The resting membrane potential was smaller in OLETF rats than in LETO rats by about 3 mV, but it was not positively related with the blood glucose level. The amplitude of hyperpolarization produced by noradrenaline (NA) was smaller in OLETF rats than in LETO rats. Transmural nerve stimulation evoked a non-adrenergic, non-cholinergic (NANC) inhibitory junction potential (i.j.p.) in both LETO and OLETF rats ; the amplitude of the i.j.p.was smaller in OLETF rats than in LETO rats, while the latency of the i.j.p.was longer in OLETF rats than in LETO rats. Thus, in the distal colon, NIDDM may cause a depolarization of the membrane, an attenuation of NANC inhibitory transmission and a reduction in reactivity of adrenoceptors to NA. These results suggest that the constipation appearing with diabetes mellitus involves dysfunction of both the enteric autonomic nerves and the smooth muscles in the colon.

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Recently, gastrointestinal motility research and various studies to measure motility have been conducted. However, it is not easy to measure the pyloric sphincter motility, especially its open and closed motility . There are few reports on the opening and closed motility of the pyloric ring . In this study, I examined the pyloric motility with strain gauge force transducers (SGTs). SGTs were implanted onto the antrum, pyloric ring and duodenum of a dog. In order to clarify the relationship between the opening and closed motility of the pylorus and SGTs recordings, the pyloric ring was observed with a gastrofiberscope while measurements were taken using the SGTs in anesthetized dogs . In addition, the pyloric ring was extended mechanically with a balloon and measurement were taken using the SGTs. In conscious dogs, the natural gastropyloroduodenal motility was recorded. Then, cisapride, erythromycin, and Leu¹³-motilin were administered in the interdigestive state and the motility was recorded . The pyloric opening and closed motility could be monitored using SGTs. The pyloric ring opened when the pyloric motility recorded using the SGTs showed a negative deflection . In addition, in phase III, when intense contraction of the antrum was observed, relaxation and opening of the pyloric ring could be observed. Erythromycin and Leu¹³-motilin induced phase III-like motility and relaxation of the pyloric ring. However, in cisapride-induced motility, relaxation of the pyloric ring was not observed. The pyloric ring opening and closed motility can be monitored using SGTs and this method is effective for the evaluation of the pyloric function.

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Contractile sensitivity to Ca²⁺ was studied in rat portal vein circular muscle isolated from normotensive Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). There was no difference in resting membrane potential between WKY and SHRSP. Elevation of extracellular K⁺ concentration induced similar increase in tension in preparations from WKY and SHRSP. High K⁺-depolarized preparation developed tension increase when extracellular Ca²⁺ concentration was increased. The sensitivity to extracellular Ca²⁺ was similar in preparations from WKY and SHRSP. Permeabilized preparation contracted when free Ca²⁺ concentration was increased. Sensitivity of permeabilized preparation to Ca²⁺ was similar in preparations from WKY and SHRSP. These results indicate that regulation of contraction by Ca²⁺ was similar between WKY and SHRSP. Since there was no change in high K-induced contraction in intact preparations or Cainduced contraction in permeabilized preparations, there seemed to be no difference in Ca²⁺ influx via voltage-dependent channels in portal vein circular muscle from WKY and SHRSP.

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