Local anesthetics and the role of @entity1372 in the force development by XXXX ventricular muscle and purkinje fibers.

@entity1169 @entity235 @entity1022 @entity8162 @entity12022 @entity4524 @entity1372 @entity13981 @entity1063
We studied the effects of the local anesthetics, @entity8162 and @entity12022 , on the action potential and force of @entity235 ventricular muscle and Purkinje fibers. In ventricular muscle, @entity8162 often shifted the plateau to a more positive value and increased the force of contraction, whereas @entity12022 shortened the action potential and decreased contractile force. In Purkinje fibers, both local anesthetics reduced contractile force and decreased the duration of the action potential markedly. In ventricular muscle fibers @entity1063 potentiated the positive inotropic effect of @entity8162 and changed the effects of @entity12022 from a negative to a positive inotropic effect. The potentiating effect of @entity8162 on contraction was eliminated by @entity1169 . In the presence of @entity1063 (and the absence of @entity1169 ), in Purkinje fibers both anesthetics decreased force but less than in the absence of @entity1063 . In the presence of @entity1022 ( @entity4524 ) and @entity1063 , @entity8162 and @entity12022 increased contractile force of muscle fibers. Under the same conditions in Purkinje fibers, @entity8162 increased contractile force and @entity12022 decreased it (but less than in the absence of @entity4524 ). Administration of @entity13981 increased contractile force in both ventricular muscle and Purkinje fibers: under these conditions, both local anesthetics decreased contractile force in both tissues. We conclude that: (1) the positive inotropic effects of @entity8162 and @entity12022 are mediated through an adrenergic mechanism; (2) the negative inotropic effect is at least in part mediated through a reduction of @entity1372 influx; and (3) the negative inotropic effect is more pronounced in Purkinje fibers because of a larger steady state @entity1372 influx during the plateau.
