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 transduct ion was investigated in human foreskin fibroblasts with endogenous PDG F beta-receptors, and porcine aortic endothelial (PAE) cells with stab ly transfected PDGF beta-receptors. Immunoprecipitation and immunoblot ting showed that PDGF induced dose-dependent autophosphorylation of PD GF beta-receptor, and that PLC-gamma associates with autophosphorylate d PDGF beta-receptors and becomes phosphorylated. Activation of PLC-ga mma is known to induce fluctuations of the concentration of cytoplasmi c calcium ([Ca2+](i)). Microfluorometry and digital imaging were emplo yed for measurements of the concentration of [Ca2+](i). In both cell t ypes the growth factor induced four types of [Ca2+](i) responses; no r ise, a small and sluggish monophasic rise, a biphasic rise with an ini tial transient peak followed by a sustained elevation, and finally reg ular oscillations. The frequencies and amplitudes of the oscillatory r esponses were independent of agonist concentration after stimulation w ith PDGF-BB. Latency, the period from application of stimulus to the f irst [Ca2+](i) peak, was reduced at higher concentrations of agonist. Also, the proportion of responding cells increased with higher concent rations of ligand. Oscillations of [Ca2+](i) were elicited at submaxim al concentrations of agonist. In PAE cells PDGF-BB triggered a single [Ca2+](i) peak in absence of external Ca2+. Ligand-induced oscillation s and sustained increases of [Ca2+](i) were counteracted by the inorga nic Ca2+ channel blocker Ce3+. These results show that similar types o f [Ca2+](i) responses occur in different cell types independently of w hether the PDGF beta-receptors are expressed endogeneously or after tr ansfection. Potentially, the different [Ca2+](i) responses have distin ct physiological consequences.