A Ca2+- and voltage-dependent cation channel in the nuclear envelope of red beet.
The patch-clamp technique was applied to study ion conductances in various configurations of the nuclear envelope of non-enzyme-treated red beet (Beta vulgaris L.) nuclei. With excised patches a non-selective cation channel was observed, that was activated by micromolar concentrations of Ca2+ on the nucleoplasmic side of the envelope. The channel activity was also voltage-dependent and the voltage threshold of channel activation changed with the nucleoplasmic Ca2+ concentration. The most prominent conductance level was 110+/-22 pS with 150 mM KCl in the bath and pipette. The channel was permeable to small cations: permeabilities relative to K+ were PK congruent with PNa=1, PCs=0.3, but PCl=0.09. Calcium ions also permeated the channel with PCa=0.43, estimated from reversal potential, or 0.14, estimated from conductance ratio. Zn2+ (1 mM) when applied to the cytoplasmic side of the envelope blocked the channel activity completely, while amiloride (2 mM) reduced the channel current by 86% from the nucleoplasmic side. The properties of the whole-nucleus current (voltage-, time- and Ca2+-dependence) paralleled those observed with excised patches. The channel may provide a Ca2+-regulated pathway for passive diffusion of cations across the nuclear envelope and thus may play an important role in Ca2+-dependent nuclear processes ranging from gene transcription to apoptosis.
Department of Biology, McGill University, 1205 Doctor Penfield Ave., Montréal, Que. H3A 1B1, Canada.
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Grygorczyk
D015220:Calcium Channels / Q000502:physiology*; D002467:Cell Nucleus / Q000502:physiology* / Q000648:ultrastructure; D019663:Chenopodiaceae / Q000502:physiology*; D015640:Ion Channel Gating; D017136:Ion Transport; D018408:Patch-Clamp Techniques
D015220:Calcium Channels