The inotropic mechanism of the phosphodiesterase inhibitor OPC 3911 alone and in combination with rolipram, studied in papillary muscles of ferret and guinea-pig and isolated myocytes of guinea-pig ventricular muscle.

OPC 3911 is a potent inhibitor and PDE III is a specific inhibitor in cardiac muscle. The effects of the drug alone and in combination with the non-inotropic PDE IV inhibitor rolipram were analysed using hearts from guinea-pigs and ferrets. OPC 3911 had an EC50 value of 0.1 microM. At 0.1 microM peak force was increased by 50.7 +/- 7.6% (n = 6, P < 0.001), time to peak tension (TPT) reduced by 18.7 +/- 5.6% (n = 6, P < 0.05). Time to half relaxation (THR) was prolonged by 19 +/- 4.2% (n = 6, P < 0.001). After addition of rolipram (30 microM), there was a potentiation of peak force at all concentrations of OPC 3911. At 0.1 microM OPC rolipram increased peak force by 82.8 +/- 8.9% (n = 6, P < 0.001), reduced TPT by 73 +/- 6% (n = 6, P < 0.005) and increased THR by 27 +/- 5% (P < 0.01). OPC 3911 shortened action potential duration (APD) at 50% repolarization by 5.3 +/- 2.5% (n = 6, P < 0.05). Addition of rolipram prolonged APD by 3.7 +/- 2.5% (n = 6, P < 0.05). Second inward current (Isi) was increased at 3 microM OPC 3911 by 46 +/- 6% (n = 6, P < 0.05). The combination of OPC 3911 and rolipram intensified the Isi to 101 +/- 5% (n = 3). Rolipram slowed the rate of restitution and the onset of restitution was prolonged. Relative maximum post-extrasystolic potentiation was reduced in the presence of OPC 3911 from 67 +/- 5% to 45 +/- 6%. Adding rolipram caused potentiation of 55 +/- 6%. OPC 3911 increased the recirculation fraction of activator calcium from 0.36 to 0.42 (n = 10, P < 0.05). After addition of rolipram the recirculation fraction was 0.41 +/- 0.04 (n = 10, P < 0.05). The results suggest that rolipram exerts its potentiating effect on OPC 3911 via an increased Isi.