Timed dose-response relationship of depressive action of ouabain on toad heart contraction in vitro.

Timed dose-response relationship (TDRR) of depressive action of ouabain (Oua) 0.01-30 mmol.L-1 on toad heart contraction in vitro was studied by simultaneous recordings of mechanical tension and electrocardiography. It was found that the inhibition of contraction tension, the latency, the half equilibrium time of depression, and the cardioplegia time (CPT) were all concentration-dependent (P <0.01). The EC50 +/- L95 of Oua was 35 +/- 8 mumol.L-1, in which L95 is the average 95% confidence limit. The TDRR data of latency or CPT were fitted to the hyperbolic 4-parameter model II weighted with the square of SE inversely: Y = 25.9492(7.2757)/(1nX + 23.5906)(6.2757) + 72.7732 for latency and Y = 20637.37/(1nX + 3.0947)(3.5907) + 196.7069 for CPT. It was concluded that the hyperbolic type of TDRR was present in Oua depressive action on the toad heart contraction in vitro.