The α2 isoform of the Na, K‐pump is involved in synchronization of smooth muscle cells in the arterial wall.

Abstract

We have hypothesized that the ouabain‐sensitive Na, K‐pump can regulate smooth muscle gap junction function. To test this hypothesis and determine the relevant isoform we investigated the effect of downregulation of the α2 isoform of Na, K‐pump.We transfected cultured smooth muscle cells (SMCs) and rat small mesenteric arteries with siRNA against the α2 isoform of Na, K‐pump and with eGFP siRNA, as a control. Paired SMCs were used as a model for electrical coupling by measuring membrane capacitance and synchronized SMC activity was assessed by measuring isometric force.Pairs of SMCs had a capacitance of 90.4±9.4pF, n=7 twice that of single cells. SMCs were uncoupled when the Na, K‐pump was inhibited by 10 μM ouabain (46.1±7.2pF). β‐glycyrrhetinic acid (βGA) had no additive effect (41.9±4.9pF). Downregulation of the α2 Na, K‐pump significantly reduced the capacitance of cell pairs (33.4±4.1pF) and made them insensitive to ouabain (34.1±4.2pF). βGA uncoupled residual coupling (28.3±3.0pF). Arteries downregulated for the Na, K‐pump had significant reduced amplitude of noradrenalin‐induced vasomotion. This is consistent with the suggested role of gap junction for synchronization of SMCs in the vascular wall.We demonstrate the importance of α2 isofom of the Na, K‐pump for intercellular coupling in the vascular wall and its involvement in the regulation of vasomotion.