Voltage-dependent effects of Ca$^2+$/calmodulin on Cl$^-$ channel in cardiac sarcoplasmic reticulum.

, and . Receptors Channels 7 (3): 189--197 (2000)


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


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