Gap junction dynamics: reversible effects of divalent cations.

Abstract

Reversible changes in gap junction structure similar to those previously seen to parallel electrical uncoupling (9,33,34) are produced by treating with Ca" or Mg" gap junctions isolated in EDTA from calf lens fibers . The changes, characterized primarily by a switch from disordered to crystalline particle packings, occur at a [Ca"] of 5-10 -7 M or higher and a [Mg"] of 110-3 M or higher and can be reversed by exposing the junctions to Ca ++ -and Mg"-free EGTA solutions. Similar changes are obtained in junctions of rat stomach epithelia incubated at 37°C in well-oxygenated Tyrode's solutions containing a Ca' ionophore (A23187) . Deep etching experiments on isolated lens junctions show that the true cytoplasmic surface of the junctions (PS face) is mostly bare, suggesting that the particles may not be connected to cytoskeletal elements . A hypothesis is proposed suggesting a mechanism of particle aggregation and channel narrowing based on neutralization of negative charges by divalent cations or H + .

Gap junction connexon configuration in rapidly frozen myocardium and isolated intercalated disks.

“…In all our experiments thejunctions were hexagonally arrayed regardless of calcium concentration, pH, or the addition of ions which normally maintain cardiac activity in perfused whole heart preparations (Kreb-Henseleit buffer was tried although its calcium concentration is relatively high compared with normal intracellular levels) . These results would suggest that in contrast to the situation proposed for eye lens junctions (25,28,29), the connexon arrangement in cardiac gap junctions appears not to be controlled by the same factors that are considered to induce functional modulation. However, no isolated junction preparation can be considered to reflect accurately the in vivo state of functionally intact junctions, and the possibility that the response of the junctions is impaired after isolation cannot be completely excluded.…”

“…Although this variable is commonly quoted in gap junction studies relating structure to function, (1, 2,4,6,7,19,22,24,25,28,29,40), the 462 THE JOURNAL OF CELL BIOLOGY " VOLUME 99, 1984 dynamic nature of the connexon configuration changes observed during our experiments makes such measurements of dubious value. There were clearly a wide range of spacings, varying from very tight packing to widely dispersed random arrays, and even variation within junctions could be equally as large.…”

“…The disks, in which the gap junctions remain surrounded by sarcolemma, were intended to provide a model system analogous to that previously used to study the effect of divalent cations and pH on eye lens junction structure (16,25,26,28,29). After isolating or incubating disks in the various media, it was necessary to stabilize the gap junctions with glutaraldehyde to prevent structural changes during the subsequent pelleting necessary for electron microscopy.…”

“…There are now many communications that document the morphology and physiology of these junctions, and particular interest has been focused on the morphological correlates of differing functional states (2, 4, 6, 7, 11, 13, 16, 19, 22, 24-29, 32, 33, 40). Several of these authors have proposed that an uncoupling of cells connected by gap junctions (and hence loss of intercellular permeability) is accompanied by an increase in the regularity ofpacking and a decrease in the center-to-center spacing of the connexons, the functional subunits that make up the junctions (2,6,(24)(25)(26)(27)(28)(29)32).…”

Connexins, cell motility, and the cytoskeleton

“…This structure implies the importance of the cytoplasmic domains for differential Cx function , which is partially achieved by variable protein-protein interaction partners. While little attention was paid to potential cytoplasmic interactions of Cxs in the past [Peracchia and Peracchia, 1980;Hirokawa and Heuser, 1982], the number of studies related to interaction of Cxs has increased dramatically. Accumulating evidence indicates that GJs are associated with a complex system of cytoplasmic and membrane (-associated) proteins, although little is known about the functional role of these interactions [for recent reviews see Giepmans, 2006;Herve et al, 2007].…”