The use of isolated mammalian cardiac myocytes for the study of inotropic mechanisms
The complex structure of cardiac muscle, in which adjacent cells are electrically coupled, is necessary to allow conduction of the action potential through the organ to initiate contraction in a controlled manner, but this complexity presents difficulties for the study of how electrical activity is coupled to contraction. The use of single myocytes isolated from their neighbours greatly simplifies the analysis of electrical activity in cardiac muscle, since the problems arising from the restricted extracellular spaces and from the syncitial nature of multicellular preparations are reduced or avoided. In the same cells, the contraction which accompanies appropriate electrical activity can be monitored using optical methods. The purpose of this communication is to discuss the mechanisms of action of agents which exert an inotropic effect, paying particular attention to the analysis of electrical activity associated with contraction in individual cardiac myocytes. We have chosen to compare the actions of inotropic agents on myocytes from rats and guinea pigs since it appears that there are some differences in excitation-contraction coupling in these two species, and these differences may shed some additional light on inotropic mechanisms in ventricular muscle.
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