Ouabain, an inhibitor of the Na⁺-pump, has been shown to inhibit intercellular communication. We have recently shown that gap junctions between vascular smooth muscle cells (SMCs) are regulated through an interaction between a ouabain-sensitive isoform of the Na⁺-pump and the Na⁺/Ca²⁺-exchanger leading to increases in [Ca²⁺]_i in discrete areas near the plasma membrane. This suggests close association of these transport proteins in microdomains.

Using PCR and co-immunoprecipitation we aimed to test this hypothesis in SMCs from mesenteric small arteries and in A7r5 cell line. Intercellular electrical coupling was evaluated in functional studies.

SMCs were electrically uncoupled when the ouabain-sensitive Na⁺-pump was inhibited by 10 mM ouabain. Inhibition of the Na⁺/Ca²⁺-exchanger with 1 mM SEA0400 also uncoupled the SMCs. Depletion of [Na⁺]_i and clamping [Ca²⁺]_i at low levels prevented the uncoupling. Ten mM ouabain evoked spatially restricted [Ca²⁺]_i transients along the cell periphery but not in the center of the cell.