Calcium induced calcium release is involved in the afterhyperpolarization in one class of guinea pig sympathetic neurone.
The mechanisms underlying two potassium conductances which are activated by Ca2+ influx during the action potential in sympathetic prevertebral neurones of guinea pigs have been investigated pharmacologically. One Ca-activated K+ conductance, which is present in all mammalian sympathetic postganglionic neurones, is maximal after the action potential and decays exponentially with a time constant of about 130 ms; this conductance was inhibited by apamin (50-100 nM) consistent with the involvement of SK channels. A second Ca-activated K+ conductance with much slower kinetics is present in a large subpopulation of coeliac neurones. This conductance was resistant to apamin but markedly inhibited by application of ryanodine (5-20 microM), suggesting that Ca2+ influx during the action potential triggers release of Ca2+ from intracellular stores which in turn activates a different class of K+ channel. Noradrenaline (100 microM) depressed the second K+ conductance selectively.
Jobling
P
P
Department of Physiology and Pharmacology, University of Queensland, Australia.
McLachlan
E M
EM
Sah
P
P
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D004594:Electrophysiology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
D012433:Ryanodine; D001030:Apamin; D002118:Calcium