Functional characterization of cell-to-cell coupling in cultured rat aortic smooth muscle

Gap junction (GJ) occurrence and function was studied in cultured rat aortic smooth muscle cells, since cell-to-cell coupling is proposed to coordinate smooth muscle function but is difficult to study in the intact tissue. Cell proliferation in vitro formed a multilayered structure 10-15 cells thick. GJs connected cells to lateral and vertical neighbors, appearing in freeze fracture as P-face particles aggregated into circular plaques but also as linear arrays. The membrane potential was 58 ± 3 mV. From quantification of the spread of electrotonic potentials according to a two-dimensional model, the intercellular resistivity was 900-1,400 Ω·cm, whereas the nonjunctional membrane resistivity was 10⁴ Ω·cm². Intercellular spread of 5(6)-carboxyfluorescein (CF; mol wt 376) in aortic cultures suggests that metabolic coupling is an important consequence of GJs in smooth muscle. CF transfer was not blocked by A23187 (10^-5 M), although rat fibroblasts became uncoupled by 10^-6 M. Ultimately uncoupled by the more potent ionophore ionomycin (10^-5 M), aortic cells seem more able to maintain GJ permeability during challenge from increased intracellular Ca than cells of noncontractile origin.