DISCUSSION
At a stimulation rate of 1 Hz, GE 70 decreased V max in guinea pig heart muscle preparations at the same concentration range as propafenone . Block of V max was use-and frequency-dependent, which is in agreement with results obtained with propafenone . The steady state inactivation curve was not shifted by GE 70, in contrast to reports of (R)- and (S)-propafenone , indicating an absence or much lower affinity of GE 70 to the inactivated sodium channel compared with propafenone. Reported time constant of recovery from the use-dependent block by propafenone in guinea pig papillary muscles and ventricular myocytes varies from 5.3 to 15.5 s. The time constant of recovery of V max from the use-dependent block by GE 70 in guinea pig papillary muscles of 6.6±0.6 s was similar to that for propafenone. Published data for propafenone and the presented data for GE 70 suggest similarities in use- and frequency-dependent block of V max and time course of recovery from that block, but differences in the voltage dependence of V max block.
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