Figure 4.

Hemichannel composition and intercellular gradient of charged cytosolic factors can lead to rectification of electrical transmission. (A,B) Heterotypic gap junction channels with steep asymmetric g_j-V_j dependence (A) facilitate or attenuate the electrical transmission of depolarizing (positive) potentials from Cell 1 to Cell 2 (1→2) or 1←2, respectively (B). The same junctions facilitate or attenuate the electrical transmission of hyperpolarizing (negative) potentials from 1←2 or 1→2, respectively (B). (C,D) Transjunctional gradient of free magnesium ion concentration ([Mg²⁺]_i) induces asymmetric g_j-V_j dependence in homotypic gap junction channels (C) that are hypersensitive to [Mg²⁺]_i, such as Cx36 gap junction channels. Electrical transmission of depolarizing potentials is facilitated from 2→1 (D), which is the opposite direction of the transjunctional [Mg²⁺]_i gradient (1→2). The same transjunctional [Mg²⁺]_i gradient facilitates the electrical transmission of hyperpolarizing potentials from 1→2 (D).