Interstitial cells of Cajal and adaptive relaxation in the mouse stomach
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Interstitial cells of Cajal (ICC) are proposed to play a role in stretch activation of nerves and are under intense investigation for potential roles in enteric innervation. Most data to support such roles come from in vitro studies with muscle strips whereas data at the whole organ level are scarce. To obtain insight into the role of ICC in distention-induced motor patterns developing at the organ level, we studied distension-induced adaptive relaxation in the isolated whole stomach of wild-type and W/W(v) mice. A method was developed to assess gastric adaptive relaxation that gave quantitative information on rates of pressure development and maximal adaptive relaxation. Pressure development was monitored throughout infusion of 1 ml of solution over a 10-min period. The final intraluminal pressure was sensitive to blockade of nitric oxide synthase, in wild-type and W/W(v) mice to a similar extent, indicating NO-mediated relaxation in W/W(v) mice. Adaptive relaxation occurred between 0.2 and 0.5 ml of solution infusion; this reflex was abolished by TTX, was not sensitive to blockade of nitric oxide synthase, but was abolished by apamin, suggesting that ATP and not nitric oxide is the neurotransmitter responsible for this intrinsic reflex. Despite the absence of intramuscular ICC (ICC-IM), normal gastric adaptive relaxation occurred in the W/W(v) stomach. Because pressure development was significantly lower in W/W(v) mice compared with wild type in all the conditions studied, including in the presence of TTX, ICC-IM may play a role in development of myogenic tone. In conclusion, a mouse model was developed to assess the intrinsic component of gastric accommodation. This showed that ICC-IM are not essential for activation of intrinsic sensory nerves nor ATP-driven adaptive relaxation nor NO-mediated relaxation in the present model. ICC-IM may be involved in regulation of (distention-induced) myogenic tone.
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