Voltage-dependent effects of Ca(2+)/calmodulin on Cl(-) channel in cardiac sarcoplasmic reticulum.
A new kind of chloride channels in the cardiac sarcoplasmic reticulum, 116 pS Cl(-) channel (500 mM Cl(-) in the cis and 50 mM Cl(-) in the trans chamber solutions), which is activated by protein-kinase-A-dependent phosphorylation, has been determined to conduct adenine nucleotide as a transporter between cytosol and SR lumen. We investigated the voltage-dependent gating of this Cl(-) channel by recording single-channel activities using the planar lipid bilayer-vesicle fusion technique. The channel activities did not change at different membrane potentials (-100 mV to +50 mV) or different Ca(2+) concentrations (1 nM to 1 mM) in cis solution. In the presence of calmodulin (CaM) (0.1 microM /microg SR vesicles), however, Ca(2+) added to the cis solution at 0 mV inhibited channel openings in a Ca(2+) -concentration-dependent manner. These effects were prevented by the addition of CaM inhibitors. The blocking effects of CaM differed depending on the membrane potentials at negative potentials below -20 mV. With CaM and 3 microM Ca(2+), the values of opening probability were 0 at -80 mV, 0.2 at -40 mV, 0.3 at -20 mV, 0.71 at 0 mV and 0.92 at +20 mV. These results may indicate the membrane potential affects the action of Ca(2+) /CaM complex
Kawano
S
S
Department of Cardiovascular Diseases Medical Research Institute Tokyo Medical and Dental University. seiko.card@mri.tmd.ac.jp
Hiraoka
M
M
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D018118:Chloride Channels / Q000187:drug effects*; D007093:Imidazoles / Q000494:pharmacology; D015640:Ion Channel Gating; D008564:Membrane Potentials; D008954:Models, Biological; D009206:Myocardium / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013552:Swine
D002147:Calmodulin; D018118:Chloride Channels; D007093:Imidazoles; C031938:calmidazolium; D002118:Calcium