Cell-to-cell communication in the heart: structure-function correlations

Summary The communicating cell junctions that ensure the electrical and diffusional continuity of the intracellular space in the heart fibres can be switched from their normal conducting, or opened state, to an exceptional non-conducting or closed state. This electrical uncoupling is observed after cell injury in the presence of Ca²⁺ ions in the extracellular fluid, after metabolic inhibition and in the presence of aliphatic alcohols (C₆ to C₉). The correlations between electrical uncoupling and gap junction morphology in the heart are briefly reviewed. A decrease of the distance between P-face particles and between the E-face pits has been found in all investigations^{3,10,16,18,55}, but the functional significance of this observation is not understood at present. A quantitatively very similar decrease of the average particle diameter (about –0.7 nm) has been measured in glutaraldehyde-fixed sheep Purkinje fibres¹⁶ and in unfixed, quickly frozen rat auricles¹⁸ that had been electrically uncoupled by three different procedures. About half of this decrease was reversible on short-term electrical recoupling (within 20 min). It is concluded that a measurable decrease of the connexon diameter correlates with electrical uncoupling.