Facilitation by isoproterenol of skeletal L-type Ca²⁺ channel openings in H9c2 cells derived from rat heart

Abstract

Objective : The H9c2 clonal cell line derived from embryonic rat ventricle is an in vitro surrogate for both cardiac and skeletal myocytes. We recorded Ca²⁺ channel currents from cell-attached patches on H9c2 cells in the myotube stage with the aim of better understanding the effect of isoproterenol on skeletal muscle L-type Ca²⁺ channel currents. Methods : Experiments were carried out using myotubules cultured for 15-50 days. Single L-type Ca²⁺ channel currents were recorded from cell-attached patches using 100 mM Ba²⁺ as the charge carrier in the presence of (+) -202-791, a pure dihydropyridine Ca²⁺ channel agonist. Results : Single L-type Ca²⁺ channel currents exhibited long open times with small (skeletal muscle) and large (cardiac) unitary amplitudes. Skeletal muscle L-type channel currents appeared more often than the cardiac channels, and the respective mean currents, which were obtained separately from patches containing both channel types, showed the skeletal muscle current rose more slowly than the cardiac current. Application of 1μ M isoproterenol increased the number of openings of both channel types. In a patch that contained numerous skeletal L-type type channels, isoproterenol increased the maximal amplitude in the current-voltage (I-V) relationship of averaged L-type Ba²⁺ currents and shifted the I-V curve towards more negative potentials. Conclusion : Skeletal L-type Ca²⁺ channels are more abundant than cardiac-type channels in H9c2 myotubes. Isoproterenola β-adrenergic agonist, increased openings in the skeletal L-type Ca²⁺ channels and their averaged currents as in the cardiac L-type Ca²⁺ channels in ventricular myocytes.