Actions of neuropeptide Y on arterioles of the guinea-pig small intestine are not mediated by smooth muscle depolarization.

Neuropeptide Y was applied to arterioles of the submucosa of the guinea-pig small intestine while arteriole diameter and smooth muscle membrane potential were monitored. Neuropeptide Y (50 nM-1 microM) caused no smooth muscle depolarization, and caused a small constriction in only 15 out of 38 arterioles studied. 50 nM Neuropeptide Y increased the amplitude of constriction caused by noradrenaline or brief trains of nerve stimulation, showing that it potentiated the effects of vasoconstrictors as it does in other arteries. The factor by which the amplitude was increased was greatest for small constrictions. Neuropeptide Y reduced the amplitude of the excitatory junction potential, suggesting that it decreased neurotransmitter release. These results show that the potentiating action of Neuropeptide Y does not depend on smooth muscle depolarization.