Expression and regulation of chloride channels in neonatal rat cardiomyocytes.

Using an 125I− efflux assay, we have studied the expression of various types of chloride channels in isolated neonatal rat cardiomyocytes. Three different classes of anion conductances were distinguished: (1) a Cal2+-sensitive Cl− conductance, triggered upon stimulation of the cells with endothelin-1 or Ca2+-ionophore; (2) a CAMP/protein kinase A-operated Cl− conductance, activated by addition of forskolin. This anion channel could be identified as the Cystic Fibrosis Transmembrane conductance Regulator (CFTR-CI− channel) by Western blotting as well as by its enhanced activity in cultures pretreated with the tyrosine kinase inhibitor genistein; (3) a distinct class of cell volume-regulated Cl− channels, potentiated in the presence of endothelin-1 or the phosphotyrosine phosphatase inhibitor pervanadate. The potential role of each class of Cl− channels in the generation and/or modulation of action potentials as well as in maintaining cell volume is discussed.