Table 3.

Effect of istaroxime on the kinetic parameters for Ca²⁺ uptake into cardiac SR vesiscles from healthy dogs by a stopped-flow method

Free Ca2+ 0.19 μM	k1 (s−1)	A1	k2 (s−1)	A2
Control N = 8	0.4117 ± 0.0379	0.003308 ± 0.00046	0.066 ± 0.0096	0.00474 ± 0.00022
+ Istar N = 8	0.5854 ± 0.0351*	0.003483 ± 0.00023	0.0841 ± 0.0067*	0.00376 ± 0.00012

Free Ca2+ 2 μM	k1 (s−1)	A1	k2 (s−1)	A2
Control N = 8	0.5523 ± 0.0449	0.00282 ± 0.000158	0.0911 ± 0.0060	0.00357 ± 0.00019
+ Istar N = 8	0.7348 ± 0.0036*	0.00341 ± 0.000258	0.1187 ± 0.0103*	0.00407 ± 0.00017

Data are mean ± SEM of absorbance at 650 nm measured in the absence (control) and presence of 100 nM istaroxime at 0.19 and 2 μM free Ca²⁺ concentrations. N, number of replicates of time course experiments; k1, rate constant for fast phase of Ca²⁺ uptake; k2, rate constant for slow phase of Ca²⁺ uptake; A1, amplitude of fast phase of Ca²⁺ uptake; A2, amplitude of slow phase of Ca²⁺ uptake. The statistical significance between control and istaroxime was measured by t-test analysis.

^*P < 0.05 istaroxime versus control.