Decreased sensitivity to beta-adrenergic stimulation of the ventricular cells isolated from the spontaneously hypertensive rat heart.

1. The stimulatory effects of isoproterenol on the L-type Ca2+ current (ICa) were compared between the control (WKY) and hypertensive (SHR) rat heart cells, using the patch-clamp method. 2. The current density and the shape of the current-voltage relationship for ICa were not different between the two groups. However, the maximal percentage increase in response to isoproterenol was smaller in SHR (+91% in SHR and +81% in WKY), and the ED50 was significantly higher in SHR (0.081 mu mol/L in SHR and 0.020 mu mol/L in WKY). IBMX, a potent phosphodiesterase inhibitor, significantly increased the isoproterenol-stimulated ICa in SHR, but not in WKY. These results suggest an impaired cAMP production in SHR heart cells.