Essential role for calcium waves in migration of human vascular smooth muscle cells

Vascular smooth muscle cell (SMC) migration is characterized by extension of the lamellipodia at the leading edge, lamellipodial attachment to substrate, and release of the rear (uropod) of the cell, all of which enable forward movement. However, little is known regarding the role of intracellular cytosolic Ca2+concentration ([Ca2+]i) in coordinating these distinct activities of migrating SMCs. The objective of our study was to determine whether regional changes of Ca2+orchestrate the migratory cycle in human vascular SMCs. We carried out Ca2+imaging using digital fluorescence microscopy of fura-2 loaded human smooth muscle cells. We found that motile SMCs exhibited Ca2+waves that characteristically swept from the rear of polarized cells toward the leading edge. Ca2+waves were less evident in nonpolarized, stationary cells, although acute stimulation of these SMCs with the agonists platelet-derived growth factor-BB or histamine could elicit transient rise of [Ca2+]i. To investigate a role for Ca2+waves in the migratory cycle, we loaded cells with the Ca2+chelator BAPTA, which abolished Ca2+waves and significantly reduced retraction, supporting a causal role for Ca2+in initiation of retraction. However, lamellipod motility was still evident in BAPTA-loaded cells. The incidence of Ca2+oscillations was reduced when Ca2+release from intracellular stores was disrupted with the sarcoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin or by treatment with the inositol 1,4,5-trisphosphate receptor blocker 2-aminoethoxy-diphenyl borate or xestospongin C, implicating Ca2+stores in generation of waves. We conclude that Ca2+waves are essential for migration of human vascular SMCs and can encode cell polarity.