Cholinergic modulation and effects of dynorphin on the non-adrenergic inhibitory potentials in the guinea-pig duodenum.

Cholinergic modulation and effects of dynorphin on the non-adrenergic non-cholinergic inhibitory potentials (NANC i.p.s) in the longitudinal smooth muscle cells of the guinea-pig duodenum were studied intracellularly. Atropine (1.4 X 10(-7)-1.4 X 10(-5) M) and scopolamine (3.3 X 10(-8)-3.3 X 10(-7) M) increased the amplitude of the evoked i.p.s while physostigmine (3.7 X 10(-7)-3.7 X 10(-6) M) and neostigmine (4.8 X 10(-8) M) decreased it. The frequency of the spontaneous action potentials in the longitudinal smooth muscle cells was increased by dynorphin (6 X 10(-8)-3 X 10(-7) M) without continuous membrane depolarization. The excitatory effect of dynorphin on the spontaneous electrical activity was not blocked by atropine (1.4 X 10(-6) M). Dynorphin (6 X 10(-8)-2.4 X 10(-7) M) increased the amplitude of the i.p.s evoked in the presence of atropine (1.4 X 10(-7)-1.4 X 10(-6) M) and in the propranolol (3.9 X 10(-6) M) solution containing atropine while dynorphin decreased the amplitude of the i.p.s evoked in the absence of atropine. In the high calcium solution containing atropine, the amplitude of the i.p.s increased. Further increase in the amplitude of the i.p.s was observed by additively applied dynorphin. However, the amplitude of the i.p.s evoked in the high calcium solution without atropine was decreased by dynorphin. These results suggest the cholinergic inhibitory modulation on the NANC inhibitory nerves in the guinea-pig duodenum, the non-cholinergic excitatory action of dynorphin on the spontaneous electrical activity of the longitudinal smooth muscle and the excitatory action of dynorphin on the NANC inhibitory nerves in the presence of muscarinic blocking agents.