Fast hyperpolarization following an excitatory postsynaptic potential in cat bladder parasympathetic neurons.
Intracellular recording techniques were used to study a fast hyperpolarizing potential following the fast excitatory postsynaptic potential evoked by an orthodromic nerve stimulation in cat bladder parasympathetic ganglion cells. In the 61 ganglion cells examined, two types of responses were recorded on stimulating the preganglionic nerve; one had only a fast excitatory postsynaptic potential (type SI, n = 20) and the other had a fast excitatory postsynaptic potential followed by a fast hyperpolarizing potential (type SII, n = 41). In type SII neurons, the half-maximum duration of the afterhyperpolarizing potential following an orthodromic spike was longer than that of a direct spike produced by injecting a depolarizing current pulse through the recording electrode; the half-maximum durations for afterhyperpolarizing potentials following orthodromic and direct action potentials were comparable in type SI cells. Blocking the initiation of an orthodromic spike by hyperpolarizing the membrane in type SII cells revealed a fast excitatory postsynaptic potential followed by a fast hyperpolarizing potential which was similar to that observed at the resting potential. The fast hyperpolarizing potential had a duration comparable to that of an afterhyperpolarizing potential following an orthodromic action potential. The fast excitatory postsynaptic potential-fast hyperpolarizing potential sequence was blocked completely and reversibly by nicotinic receptor antagonists (hexamethonium and D-tubocurarine). Atropine, alpha-2 noradrenergic (yohimbine and phentolamine), and purinergic (caffeine) antagonists had no effect on the fast hyperpolarizing potential. In cells which show type SII responses, spontaneous excitatory postsynaptic potentials were not followed by a hyperpolarization. Depolarizing the membrane (by passing a cathodal current through the recording electrode) to an amplitude comparable to that of a fast excitatory postsynaptic potential also did not elicit a membrane hyperpolarization in type SII cells. In some cells, stimulating one preganglionic nerve trunk elicited a fast hyperpolarizing potential, but activating another nerve trunk innervating the same ganglion cell did not. There was no correlation between the variations in the amplitudes of the fast excitatory postsynaptic potential and the fast hyperpolarizing potential in type SII cells, but increasing the stimulus intensity applied to the presynaptic nerve fiber potentiated the amplitude of the fast excitatory postsynaptic potential and the fast hyperpolarizing potential. The fast hyperpolarizing potential was not associated with appreciable changes in input resistance.(ABSTRACT TRUNCATED AT 400 WORDS)
Kumamoto
E
E
Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston 77550.
Nohmi
M
M
Shinnick-Gallagher
P
P
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002415:Cats; D002799:Cholinergic Fibers / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D005726:Ganglia, Parasympathetic / Q000187:drug effects / Q000502:physiology*; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009433:Neural Inhibition; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology*; D014403:Tubocurarine / Q000494:pharmacology; D001743:Urinary Bladder / Q000294:innervation*
D006584:Hexamethonium Compounds; D011978:Receptors, Nicotinic; D018738:Hexamethonium; D014403:Tubocurarine