Smooth muscle gap-junctions allow propagation of intercellular Ca2+ waves and vasoconstriction due to Ca2+ based action potentials in rat mesenteric resistance arteries

Abstract

The role of vascular gap junctions in the conduction of intercellular Ca²⁺ and vasoconstriction along small resistance arteries is not entirely understood. Some depolarizing agents trigger conducted vasoconstriction while others only evoke a local depolarization. Here we use a novel technique to investigate the temporal and spatial relationship between intercellular Ca²⁺ signals generated by smooth muscle action potentials (APs) and vasoconstriction in mesenteric resistance arteries (MA). Pulses of exogenous KCl to depolarize the downstream end (T1) of a 3 mm long artery increased intracellular Ca²⁺ associated with vasoconstriction. The spatial spread and amplitude of both depended on the duration of the pulse, with only a restricted non-conducting vasoconstriction to a 1 s pulse. While blocking smooth muscle cell (SMC) K⁺ channels with TEA and activating L-type voltage-gated Ca²⁺ channels (VGCCs) with BayK 8644 spread was dramatically facilitated, so the 1 s pulse evoked intercellular Ca²⁺ waves and vasoconstriction that spread along an entire artery segment 3000 μm long. Ca²⁺ waves spread as nifedipine-sensitive Ca²⁺ spikes due to SMC action potentials, and evoked vasoconstriction. Both intercellular Ca²⁺ and vasoconstriction spread at circa 3 mm s^-1 and were independent of the endothelium. The spread but not the generation of Ca²⁺ spikes was reversibly blocked by the gap junction inhibitor 18β-GA. Thus, smooth muscle gap junctions enable depolarization to spread along resistance arteries, and once regenerative Ca²⁺-based APs occur, spread along the entire length of an artery followed by widespread vasoconstriction.

Keywords: Gap junctions; Intercellular Ca(2+)waves; Mesenteric resistance artery; Spreading vasoconstriction.