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The coupling coefficient is a measure of synaptic strength of an electrical synapse. It equals the ratio of the postsynaptic voltage response over the presynaptic voltage stimulus of two electrically coupled cells.
Because of the low-pass frequency filter characteristics of an electrical synapse, its coupling coefficient depends on the frequency characteristics of the stimulus. The steady-state coupling coefficient for direct current (DC) stimuli (i.e., stimulus frequency = 0) is a function of the electrical resistance of the gap junction and the input resistance of the postsynaptic cell. The non-steady state solution of the coupling coefficient for alternating current (AC) stimuli (i.e., stimulus frequency ≠ 0) includes capacitance terms represented by the membrane capacitance of the postsynaptic cell.