Figure 21.

Freeze fracture images of gap junctions from rat stomach epithelium. In controls, most gap junctions display particles (connexons) and pits irregularly packed at center-to-center spacing of 103-105 Å (A). In cells uncoupled by 1 h treatment with 2,4-dinitrophenol (DNP) particles and pits aggregate into crystalline, hexagonal, arrays with an average center-to-center spacing of ~85 Å (B). We propose that while in coupled conditions CaM is linked to each of the 6 connexins (A, inset), with high [Ca²⁺]_i all of the CaM molecules, but the gating one, might detached from connexins, allowing the channels to tightly pack into crystalline (hexagonal) arrays (B, inset). P and E: Protoplasmic and Exoplasmic faces, respectively. Adapted from Ref. [182].