Diltiazem and contraction in cat ventricular muscle during experimentally induced right ventricular systolic hypertension

The effects of diltiazem (2.2 X 10(-7) and 2.2 X 10(-6) M) on isometric contraction and K+-induced contracture (Pc) were determined for right ventricular muscles from normal cats and cats with right ventricular systolic hypertension (RVSH) monitored 4-15 days after partial pulmonary artery obstruction. Muscles obtained from cats with RVSH had significantly decreased maximum isometric force (Po) and maximum rate of force development (dF/dt). Diltiazem (2.2 x 10(-7) and 2.2 x 10(-6) M) significantly reduced Pc of both normal and pressure-overloaded muscle. Po of normal muscle was decreased only by 2.2 X 10(-6) M, while Po of pressure-overloaded muscle was significantly reduced at a lower concentration (2.2 X 10(-7) M0. The effect of diltiazem was reversed by increases to [Ca2+]0. These results demonstrate that contractile function of pressure-overloaded ventricular myocardium is more sensitive to diltiazem.