Intracellular calcium transients are necessary for platelet-derived growth factor but not extracellular matrix protein-induced vascular smooth muscle cell migration

Purpose Vascular smooth muscle cell (SMC) migration is a critical component of the hyperplastic response that leads to recurrent stenosis after interventions to treat arterial occlusive disease. We investigated the relationship between intracellular calcium ([Ca²⁺]_i) and migration of vascular SMCs in response to platelet-derived growth factor (PDGF) and extracellular matrix (ECM) proteins. Methods Human saphenous vein SMCs were used for all experiments. SMC migration in response to agonists was measured with a microchemotaxis assay. A standard fluorimetric assay was used to assess changes in [Ca²⁺]_i in response to the various combinations of growth factors and ECM proteins. Results The calcium ionophore A23187 produced a rapid rise in [Ca²⁺]_i and a corresponding 60% increase in SMC migration, whereas chelation of [Ca²⁺]_i with BAPTA (1,2-bis [aminophenoxy] ethane-N,N,N′,N′-tetraacetic acid) produced a fivefold decrease in PDGF-induced chemotaxis, suggesting that [Ca²⁺]_i is both sufficient and necessary for SMC migration. Stimulation of SMCs with PDGF produced an early peak followed by a late plateau in [Ca²⁺]_i. To establish a relationship between temporal fluctuations in [Ca²⁺]_i and SMC migration, SMCs were pretreated with caffeine and ryanadine, which eliminated the initial peak but not the late plateau in [Ca²⁺]_i, and had no effect on chemotaxis in response to PDGF. Incubation of SMCs with nickel chloride eliminated the late plateau, but had no effect on the initial peak in [Ca²⁺]_i, and reduced PDGF-stimulated migration by fivefold. We then evaluated the role of calcium in SMC migration induced by ECM proteins such as laminin, fibronectin, and collagen types I and IV. All four matrix proteins stimulated SMC migration, but none produced an elevation in [Ca²⁺]_i. Moreover, preincubation of SMCs with caffeine and ryanadine or nickel chloride had no effect on ECM protein-induced chemotaxis. Conclusion [Ca²⁺]_i transients are necessary for PDGF but not ECM protein-induced SMC chemotaxis. Moreover, the ability of PDGF to stimulate vascular SMC migration appears dependent on influx of extracellular calcium through membrane channels.