In this chapter we reviewed the effects of external fields on voltage and Ca2+ responses of isolated cardiac cells and cell-pairs. Although the focus of our discussion has been cardiac cell, the concepts and framework presented should have broader applications for other excitable cell systems as well. For example, decomposition of responses into active and passive components should be applicable to any excitable cell except that the details of the active component, which depend on ion channel mix and their current-voltage characteristics, could vary among cells. The effect of intercellular junction on field-induced responses and sawtooth effect also has fundamental biophysical underpinning, and hence should have applications in other cell systems containing gap junctions, which are known to express in almost every tissue type in the body.87 The only requirement is that gap junction should be the site of resistive discontinuity. Finally, because Ca2+ is such an important ion for the various cellular signaling and functions, and voltage-dependent Ca2+ is an important player via which exquisite regulation of Ca2+ is accomplished, the field-induced gradients in intracellular Ca2+ may be a phenomenon that is not just restricted to a cardiac cell, but instead may be universal to all cell types when stimulated with electric fields of appropriate strengths.

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