Morphological, biochemical, and electrophysiological characterization of a clonal cell (H9c2) line from rat heart

Morphological, electrophysiological, and biochemical properties of H9c2 cells, a permanent cell line derived from rat cardiac tissue, were studied. Although the lectin binding pattern revealed similar sugar residues in the surface coat of H9c2 cells and isolated rat cardiocytes, heart-specific morphological structures could not be detected in H9c2 cells. Under physiological ionic conditions, H9c2 cells exhibited an outwardly rectifying, transient K⁺ current. When this current component was blocked by Ba²⁺ and Cs⁺, we observed an inward current through Ca²⁺ channels (15.8 ± 2.2 pA/pF, n = 18, measured as Ba²⁺ current) that showed all characteristics of cardiac L-type currents. The activation kinetics were fast, and the current was stimulated by isoproterenol. The effect of isoproterenol was mimicked by forskolin or intracellularly applied cAMP. In radioligand binding experiments, we identified a specific, saturable, stereoselective and reversible high-affinity [³H]-(+)PN 200-110 binding with a dissociation constant K(d) = 0.53 ± 0.28 nM and a maximal specific binding of B(max)=129.3 ± 16.1 fmol/mg protein. There was an additional low-affinity/high-capacity binding site, which is unlikely to be related to a Ca²⁺ channel protein. Signal-transducing G proteins in membranes were characterized by [³²P]ADP-ribosylation catalyzed by bacterial toxins and by the use of various antibodies. Cholera toxin substrates of 42 and 45 kd were identified that apparently correlated to G(s) α-subunits. Pertussis toxin substrates of 40-41 kd were tentatively identified as G(i) α-subunits. The G protein G(o) was absent or at least extremely low in concentration.