PDGF-BB TRIGGERED CYTOPLASMIC CALCIUM RESPONSES IN CELLS WITH ENDOGENOUS OR STABLY TRANSFECTED PDGF BETA-RECEPTORS

Platelet-derived growth factor-BE (PDGF-BB) triggered signal transduction was investigated in human foreskin fibroblasts with endogenous PDGF beta-receptors, and porcine aortic endothelial (PAE) cells with stably transfected PDGF beta-receptors. Immunoprecipitation and immunoblotting showed that PDGF induced dose-dependent autophosphorylation of PDGF beta-receptor, and that PLC-gamma associates with autophosphorylated PDGF beta-receptors and becomes phosphorylated. Activation of PLC-gamma is known to induce fluctuations of the concentration of cytoplasmic calcium ([Ca2+](i)). Microfluorometry and digital imaging were employed for measurements of the concentration of [Ca2+](i). In both cell types the growth factor induced four types of [Ca2+](i) responses; no rise, a small and sluggish monophasic rise, a biphasic rise with an initial transient peak followed by a sustained elevation, and finally regular oscillations. The frequencies and amplitudes of the oscillatory responses were independent of agonist concentration after stimulation with PDGF-BB. Latency, the period from application of stimulus to the first [Ca2+](i) peak, was reduced at higher concentrations of agonist. Also, the proportion of responding cells increased with higher concentrations of ligand. Oscillations of [Ca2+](i) were elicited at submaximal concentrations of agonist. In PAE cells PDGF-BB triggered a single [Ca2+](i) peak in absence of external Ca2+. Ligand-induced oscillations and sustained increases of [Ca2+](i) were counteracted by the inorganic Ca2+ channel blocker Ce3+. These results show that similar types of [Ca2+](i) responses occur in different cell types independently of whether the PDGF beta-receptors are expressed endogeneously or after transfection. Potentially, the different [Ca2+](i) responses have distinct physiological consequences.