K+-evoked taurine efflux from cerebellar astrocytes: On the roles of Ca2+ and Na+ |
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Authors: | Robert A Philibert Keith L Rogers Gary R Dutton |
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Institution: | (1) Department of Pharmacology, College of Medicine, University of Iowa, 52242 Iowa City, IA, USA;(2) Department of Psychiatry, College of Medicine, University of Iowa, 52242 Iowa City, IA, USA |
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Abstract: | The ionic requirements for K+-evoked efflux of endogenous taurine from primary cerebellar astrocyte cultures were studied. The Ca2+ ionophore A23187 evoked taurine efflux in a dose-dependent fashion with a time-course identical to that of K+-induced efflux. The Ca2+-channel antagonist nifedipine had no effect upon efflux induced by 10 or 50 mM K+. In addition, verapamil did not antagonize 50 mM K+-evoked efflux except at high, non-pharmacological concentrations (>100 M), and preincubation with 2 M -conotoxin had no effect on 50 mM K+-evoked efflux. Similarly, preincubation with 1 mM ouabain had no effect on the amount of taurine released by K+ stimulation, but did accelerate the onset of efflux by 2–4 min. Although 2 M tetrodotoxin had no effect on K+-evoked release, replacing Na+ with choline abolished the taurine efflux seen in response to K+ stimulation. Together, these findings suggest that neuronal N- and L-type Ca2+- and voltage-dependent Na+-channels are not involved in the influx of Ca2+ which appears to be necessary for K+-evoked taurine efflux, and that in addition to Ca2+, extracellular Na+ is also required. |
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Keywords: | Astrocytes cerebellum taurine primary cell culture Ca2+-channel blockers |
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