The findings of the present study suggest that NO is released during NANC nerve stimulation, but plays no role in NANC relaxations in the guinea-pig taenia coli unless the effects of another apamin- sensitive, nerve-derived hyperpolarizing factor (NDHF) are blocked. Thus, we propose that in this tissue, No acts as a 'backup' or redundant NANC nerve inhibitory transmitter and like NDHF mediates relaxation via hyperpolarization.
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