Studies in Isolated Purkinje Fibers

Purkinje fibers are excised from the isolated heart and placed in a superfusion chamber with warmed (37 °C) Tyrode s solution containing 4mM potassium and a flow rate of 8-10ml/min. The fibers are stimulated using platinum electrodes at 2 times threshold for 1-2 ms using a biphasic wave form. The fibers are then 

CRITICAL ASSESSMENT OF THE METHOD The Purkinje fiber is a non-contractile tissue, which facilitates electrode positioning and stability. In comparison to the papillary muscle or the monophasic action potential in the intact heart, drug-induced effects on the action potential duration are considerably larger. Whereas this is not necessarily a disadvantage, the model has been viewed as possibly being too sensitive for drug-induced effects on repolarization. 

The basic experimental approach is suitable using Purkinje fibers from a variety of species including in addition to the dog, the rabbit and pig. The use of primate tissue for such studies carries with it some ethical and financial considerations, as does, in fact the use of dog purkinje fibers in certain countries. 

Studies in isolated rabbit Purkinje fibers were recommended to assess the risk of QT interval prolongation by drugs (Adamantidis et al. 1995, 1998 Cavero et al. 1999 Dumotier et al. 1999 Champeroux et al. 2000). 

The studied drug is added to the Tyrode s solution in increasing cumulative concentrations, each concentration being tested for 30 min. The stimulation frequency is 60 pulses per min except between the 20th and 22nd min, when the frequency is reduced to 12 and then switched back to 60 pulses per min. Action potentials are measured after 15 and 30 min of each concentration superfusion and at the end of the 2-min stimulation of 12 pulses per min. 

---