Propagation of Fast and Slow Intercellular Calcium Waves in Primary Cultured Smooth Muscle Cells

Abstract

Tissue blood flow is controlled by the changes in the diameter of the arteries and arterioles due to the coordinated contraction and relaxation of smooth muscle cells (SMCs) within the vascular wall. The contractile state of SMCs is regulated primarily by the intracellular Ca2+ concentration ([Ca2+]i). The increase in [Ca2+]i in response to hormonal stimuli propagates from cell to cell along the vessel wall as a wave, and activates the process of contraction. The mechanism underlying this phenomenon, however, is not yet fully revealed.In this work, we study the onset and propagation of intercellular calcium waves through gap junctions in primary cultured vascular SMCs. For imaging intercellular Ca2+ waves, SMCs seeded along a collagen line and loaded with the fluorescent Ca2+ indicator Fluo-4 were locally stimulated mechanically or chemically. The stimulation evoked two distinct calcium waves: 1) a fast Ca2+ wave (several mm/s), and 2) a much slower Ca2+ wave (few tens of μm/s); both waves propagated to neighboring cells. The fast Ca2+ wave was caused by the propagation of membrane depolarization and subsequent Ca2+ influx through voltage operated channels. This fast wave facilitated the onset and propagation of a slow, but higher amplitude Ca2+ wave that started from the stimulated cell and propagated to neighboring cells. Our results suggest a possible mechanism for intercellular Ca2+ wave propagation through gap junction channels in SMCs.