Calcium efflux through cardiac calcium channels reconstituted into liposomes--flux measurement with fura-2.

Cardiac Ca2+ channels were solubilized and reconstituted into liposomes, and Ca2+ efflux from the proteoliposomes was measured with the fluorescent dye fura-2. The Ca2+ efflux, induced by K+ depolarization, was sensitive to Ca2+ channel modulators such as nifedipine, D-600 and Bay K 8644, and was dependent on the membrane potential. Furthermore, the efflux was increased by phosphorylation of proteoliposomes with cAMP-dependent protein kinase. These results suggest that the reconstituted cardiac Ca2+ channels retain the voltage-dependent gating properties, pharmacological sensitivities and modulation by phosphorylation.