Alterations of excitation-contraction coupling by platelet-derived growth factor in enzymatically isolated and cultured vascular smooth muscle cells

Abstract

We studied stimulus-specific alterations of the excitation-contraction coupling pathway in freshly isolated contractile and subcultured non-contractile vascular smooth muscle cells. Using the calcium indicator aequorin, we detected physiological increases in cytoplasmic free calcium ([Ca²⁺]_i) in subcultured smooth muscle cells subjected to angiotensin or 33 mM potassium depolarization. These increases were qualitatively identical to those previously measured in intact vascular strips. Platelet-derived growth factor (PDGF) induced a slow, sustained [Ca²⁺]_i increase when applied to the subcultured smooth muscle cells at low picomolar concentrations. Freshly isolated, contractile vascular smooth muscle cells, prepared by a novel technique, exhibited a slow shortening of 20% of resting length in response to PDGF. PDGF also markedly potentiated smooth muscle cell shortening in response to an ED₅₀ dose of phenylephrine. This effect was PDGF concentration dependent. The time course of shortening induced by PDGF alone was consistent with the time course of the PDGF-induced [Ca²⁺]_i increase in the cultured smooth muscle cells. These data suggest that agonists which induce [Ca²⁺]_i changes in contractile smooth muscle cells may retain this ability with respect to cultured smooth muscle cells. PDGF, a peptide mitogen for proliferative smooth muscle cells, may also serve to modulate vascular tone by modestly raising [Ca²⁺]_i in contractile smooth muscle cell and, therefore, sensitizing the cells to alpha adrenergic agonists.