Nitric oxide and nitrosocysteine mimic nonadrenergic, noncholinergic hyperpolarization in canine proximal colon

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Abstract
Previous evidence suggests that nonadrenergic, noncholinergic (NANC) inhibitory neurotransmission in visceral muscles may be mediated by nitric oxide (NO). We have demonstrated that NO and the NO carrier S-nitrosocysteine can mimic the hyperpolarization in colonic muscle caused by nerve stimulation. The finding that S-nitrosocysteine breaks down fast enough to cause inhibitory junction potential (IJP)-like hyperpolarizations suggests that NO could be stored as a nitrosothiol in secretory vesicles in nerve terminals. Oxyhemoglobin blocked hyperpolarization responses to NO and S-nitrosocysteine and NANC IJPs. These findings suggest that NO is a biologically active transmitter substance in NANC inhibitory neurotransmission. NO enhanced the open probability of Ca(2+)-activated K+ channels in isolated colonic muscle cells. These channels may mediate the hyperpolarization response to NANC neurotransmission in colonic muscles.

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