Reconstitution of a voltage-activated calcium conducting cation channel from brain microsomes.
Many aspects of nerve cell function are controlled by cytosolic Ca2+. Intracellular organelles can sequester the cation and release it in a regulated fashion through specific ion channels including ryanodine-sensitive and inositol trisphosphate (InsP3)-activated intraneuronal Ca2+ channels. We have now used the planar bilayer technique to characterize a distinct high-conductance Ca2+ channel from brain microsomal membranes, which was not found in synaptic plasma membranes. Channel conductance in 50 mM CaCl2 is approximately 100 pS. The channel is permeable to Ca2+, Ba2+, K+ and Cs+, but it is not ideally cation-selective (PCs+:PCl- = 4:1). It opens in bursts in a steeply voltage-dependent manner, with maximal activation around zero mV. Channel activity is unaffected by caffeine or ryanodine (both of which modify the gating of ryanodine-sensitive Ca2+ channels), or by InsP3 or heparin (which act on InsP3-sensitive Ca2+ channels). omega-conotoxin GVIA, ruthenium red, amiloride and procaine all block the channel, the latter two by interacting with one or more negatively-charged binding sites in the voltage gradient within the channel pore. We suggest the channel may have a role in intracellular Ca(2+)-signalling, possibly linked to the operation of intracellular Ca2+ stores.
Martin
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Department of Biochemistry, University of Edinburgh, UK.
Ashley
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RH
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000648:ultrastructure; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002412:Cations / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D008051:Lipid Bilayers; D008564:Membrane Potentials / Q000187:drug effects; D008861:Microsomes / Q000378:metabolism*; D009482:Neurophysiology / Q000379:methods; D010455:Peptides / Q000494:pharmacology; D011343:Procaine / Q000494:pharmacology; D051381:Rats; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D015290:Second Messenger Systems; D020866:omega-Conotoxin GVIA
D015220:Calcium Channels; D002412:Cations; D008051:Lipid Bilayers; D010455:Peptides; D012430:Ruthenium Red; D012433:Ryanodine; D011343:Procaine; D000584:Amiloride; D015544:Inositol 1,4,5-Trisphosphate; D020866:omega-Conotoxin GVIA