Propagation of fast and slow intercellular Ca2+ waves in primary cultured arterial smooth muscle cells

Smooth muscle contraction is regulated by changes in cytosolic Ca2+ concentration ([Ca2+]i). In response to stimulation, Ca2+ increase in a single cell can propagate to neighbouring cells through gap junctions, as intercellular Ca2+ waves. To investigate the mechanisms underlying Ca2+ wave propagation between smooth muscle cells, we used primary cultured rat mesenteric smooth muscle cells (pSMCs). Cells were aligned with the microcontact printing technique and a single pSMC was locally stimulated by mechanical stimulation or by microejection of KCl. Mechanical stimulation evoked two distinct Ca2+ waves: (1) a fast wave (2 mm/s) that propagated to all neighbouring cells, and (2) a slow wave (20 μm/s) that was spatially limited in propagation. KCl induced only fast Ca2+ waves of the same velocity as the mechanically induced fast waves. Inhibition of gap junctions, voltage-operated calcium channels, inositol 1,4,5-trisphosphate (IP3) and ryanodine receptors, shows that the fast wave was due to gap junction mediated membrane depolarization and subsequent Ca2+ influx through voltage-operated Ca2+ channels, whereas, the slow wave was due to Ca2+ release primarily through IP3 receptors. Altogether, these results indicate that temporally and spatially distinct mechanisms allow intercellular communication between SMCs. In intact arteries this may allow fine tuning of vessel tone.

► Propagation mechanism of calcium waves between arterial smooth muscle cells. ► Mechanical stimulation induced two different calcium waves; a fast and a slow wave. ► The fast wave is due to membrane depolarization and subsequent calcium entry. ► The slow wave is due to calcium release primarily through IP3 receptors. ► Smooth muscle cells communicate by temporally and spatially distinct mechanisms.