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

Summary 1. The stirnulatory effects of isoproterenol on the L-type Ca2+ current (Ic.) 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 Ic. 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 μmol/L in SHR and 0.020 μmol/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.