ISSN:
1432-1424
Keywords:
Xenopus oocytes
;
Cl− channel
;
Divalent cations
;
Leak current
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract Defolliculated oocytes of Xenopus laevis responded to removal of external divalent cations with large depolarizations and, when voltage clamped, with huge currents. Single channel analysis revealed a Cl− channel with a slope conductance of about 90 pS at positive membrane potentials with at least four substates. Single channel amplitudes and mean channel currents had a reversal potential of approximately −15 mV as predicted by the Nernst equation for a channel perfectly selective for Cl−. Readdition of Ca2+ immediately inactivated the channel and restored the former membrane potential or clamp current. The inward currents were mediated by a Ca2+ inactivated Cl− channel (CaIC). The inhibitory potency of Ca2+ was a function of the external Ca2+ concentration with a half maximal blocker concentration of about 20 μm. These channels were inhibited by the Cl− channel blockers flufenamic acid, niflumic acid and diphenylamine-2-carboxylate (DPC). In contrast, 4,4′-acetamido-4′-isothiocyanatostilbene-2,2′-disulfonicacid (SITS), another Cl− channel blocker, led to activation of this Cl− channel. Like other Cl− channels, the CaIC was activated by cytosolic cAMP. Extracellular ATP inhibited the channel while ADP was without any effect. Injection of phorbol 12-myristate 13-acetate (PMA), a protein kinase C activating phorbol ester, stimulated the Cl− current. Cytochalasin D, an actin filament disrupting compound, reversibly decreased the clamp current demonstrating an influence of the cytoskeleton. The results indicate that removal of divalent cations activates Cl− channels in Xenopus oocytes which share several features with Cl− channels of the CLC family. The former so-called leak current of oocytes under divalent cation-free conditions is nothing else than an activation of Cl− channels.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00235044
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