ABSTRACT
Voltage-dependent gating of gap junction channels has been observed in a number of experimental preparations. In heart, however, most authors agree that junctional conductance is not voltage dependent. This chapter discusses the development of heart gap junctions consisting of relatively few junctional channels, voltage dependence is observed when the transjunctional voltage difference exceeds 50 mV. The experiment illustrates that voltage dependence of the junctional channels is not lost when they are incorporated in large arrays. To explain this it should be considered that the tightly packed channels form regions of low intercellular resistance. The question arises which fraction of the voltage, applied between electrodes placed in two neighboring cells connected by a gap junction, is actually "sensed" by the gating particles of the gap junction channels. To answer this question the chapter calculates the electrical field in and near gap junctions of different sizes ranging from one to a few hundred channels.
