Evidence against vasoactive intestinal polypeptide being the non-adrenergic, non-cholinergic inhibitory transmitter released from nerves supplying the smooth muscle of the guinea-pig taenia coli.
Vasoactive intestinal polypeptide (VIP), located within intrinsic neurones of the guinea-pig taenia coli, has been proposed as a neurotransmitter which may mediate certain non-adrenergic, non-cholinergic effects within the gastrointestinal tract. The relaxation of the taenia coli produced by exogenous VIP has a longer latency and time to maximum than the relaxation which is obtained during electrical stimulation of the non-adrenergic, non-cholinergic nerves. The responses to exogenous VIP (0.03-1 microM) were abolished by the proteolytic enzyme alpha-chymotrypsin (1 U/ml), whereas there were no statistically significant changes in the inhibitory responses to intramural nerve stimulation (0.1-5 Hz) or exogenous ATP (0.03-100 microM), which closely mimics the nerve-mediated response. Apamin is a neurotoxin which prevents the increase in K+ conductance associated with the inhibitory junction potential produced by stimulation of the non-adrenergic, non-cholinergic inhibitory nerves. In the presence of apamin (0.005-1 microM) the responses to intramural nerve stimulation and exogenous ATP were significantly antagonised, and often converted to contractile responses. The VIP-induced relaxations during apamin treatment were not significantly decreased. These results suggest that VIP is unlikely to be the transmitter released from the non-adrenergic, non-cholinergic nerves of the guinea-pig taenia coli, and are consistent with the view that these nerves are purinergic in nature.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002918:Chymotrypsin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D005768:Gastrointestinal Hormones / Q000502:physiology*; D006168:Guinea Pigs; D007422:Intestines / Q000294:innervation*; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects; D018377:Neurotransmitter Agents / Q000378:metabolism / Q000502:physiology*; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*
D005768:Gastrointestinal Hormones; D018377:Neurotransmitter Agents; D001030:Apamin; D014660:Vasoactive Intestinal Peptide; D000255:Adenosine Triphosphate; D002918:Chymotrypsin