@entity934 lengthens action potentials of XXXX cardiac Purkinje fibers.

@entity4033 @entity742 @entity1617 @entity3897 @entity15071 @entity934
The effect of @entity934 ( @entity1617 ) on the electrical activity of @entity742 cardiac Purkinje fibers was studied using standard microelectrode techniques. Most fibers showed a definite sequence of changes when exposed to @entity1617 . Initially, action potential duration (APD) increased markedly. After about 20 s, the @entity15071 ( @entity15071 ) started to become more negative and, at the same time, the rate of increase in APD slowed. Once the @entity15071 stabilized at a more negative level, the APD usually resumed its rapid increase. @entity1617 also increased the slope of diastolic depolarization and made the plateau voltage more positive. APD was increased by @entity1617 concentrations as low as 10(-7) M, and it increased with concentrations up to 10(-5) M (the highest concentration tested). @entity1617 -induced increases in APD depended on the stimulation frequency; 2-min exposures to 10(-6) M @entity1617 increased APD by 76.8 +/- 14.7% at 6 min-1 and 17.7 +/- 4.2% at 60 min-1. @entity3897 blocked all the effects of @entity1617 . @entity4033 did not prevent the @entity1617 effects. It is concluded that @entity1617 acts via muscarinic receptors. The changes in APD and @entity15071 appear to be separate events, and it is difficult to see how the former effect may be explained by known actions of @entity1617 .
