EXPRESSION AND REGULATION OF CHLORIDE CHANNELS IN NEONATAL RAT CARDIOMYOCYTES

Using an I-125- efflux assay, we have studied the expression of variou s types of chloride channels in isolated neonatal rat cardiomyocytes. Three different classes of anion conductances were distinguished: (1) a Ca2+-sensitive Cl- conductance, triggered upon stimulation of the ce lls with endothelin-1 or Ca2+-ionophore; (2) a cAMP/protein kinase A-o perated Cl- conductance, activated by addition of forskolin. This anio n channel could be identified as the Cystic Fibrosis Transmembrane con ductance Regulator (CFTR-CI- channel) by Western blotting as well as b y its enhanced activity in cultures pretreated with the tyrosine kinas e inhibitor genistein; (3) a distinct class of cell volume-regulated C l- channels, potentiated in the presence of endothelin-1 or the phosph otyrosine phosphatase inhibitor pervanadate. The potential role of eac h class of Cl- channels in the generation and/or modulation of action potentials as well as in maintaining cell volume is discussed.