Two calcium-sensitive spike after-hyperpolarizations in visceral sensory neurones of the rabbit.
Intracellular recordings were made from rabbit nodose neurones in vitro. Two temporally distinct spike after-hyperpolarizations (a.h.p.s) were identified in a subpopulation of C-type neurones. The fast a.h.p. after a single spike lasted no longer than 500 ms, while the slow a.h.p. persisted for seconds. Both a.h.p.s. were increased in amplitude in low K+ (0.56 mM) solutions and decreased in amplitude in high K+ (11.2 mM) solutions, and both were reversed at hyperpolarized membrane potentials. The slow a.h.p. was reduced in low Ca2+ (0.22 mM), in the presence of Ca2+ antagonists (Ni2+, 1 mM; Cd2+, 100 microM; or Co2+, 1 mM) and was enhanced in tetraethylammonium (5 mM). In approximately half of the cells tested, the fast a.h.p. was reduced in low Ca2+ and in the presence of the Ca2+ antagonists. In the remaining cells the fast a.h.p. was insensitive to these procedures. Prostaglandin (PGE1, 1-10 micrograms/ml) reduced the slow a.h.p. in all cells tested. Neither the Ca2+-sensitive nor the Ca2+-insensitive fast a.h.p. was affected by the prostaglandin. It is concluded that there is a subpopulation of C-type nodose neurones possessing a slow a.h.p. which is due to a Ca2+-dependent K+ current. This subpopulation of neurones can further be divided on the basis of the presence of a Ca2+-sensitive fast a.h.p. Furthermore, PGE1 pharmacologically separates the fast and slow a.h.p.s by selectively blocking the slow one. The blockage by the PGE1 is most probably not due to a reduction in Ca2+ influx.
D000200:Action Potentials / Q000187:drug effects; D000527:Alprostadil; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009475:Neurons, Afferent / Q000502:physiology*; D009620:Nodose Ganglion / Q000166:cytology*; D011188:Potassium / Q000494:pharmacology; D011458:Prostaglandins E / Q000494:pharmacology; D011817:Rabbits; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013997:Time Factors; D014630:Vagus Nerve / Q000166:cytology*
D002121:Calcium Channel Blockers; D011458:Prostaglandins E; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D000527:Alprostadil; D011188:Potassium; D002118:Calcium