Increase of (Ca2+ +Mg2+)-ATPase activity of renal basolateral membranes by platelet-derived growth factor through a...

Studies were made on the direct effect of platelet-derived growth factor (PDGF) on the high-affinity (Ca2+ +Mg2+)-ATPase, a membrane bound Ca2+-extrusion pump enzyme of the basolateral membranes (BLM) of canine kidney (Km for free Ca2+ = 1.0 x 10(-7) M, Vmax = 180 nmol Pi/mg/min). At 1 x 10(-7) M free Ca2+, PDGF (10(-10)-10(-8) M) stimulated the enzyme activity significantly. Addition of 5 - 200 microM suramin, a compound that blocks binding of PDGF to its receptors on cell membranes, inhibited the stimulatory effect of PDGF dose-dependently (IC50 = 40 microM). A high affinity specific receptor for PDGF (Kd = 4.4 x 10(-10) M, Bmax = 460 fmol/mg protein) was detected on BLM preparations by radioreceptor assay with 125I-PDGF and unlabelled PDGF. Suramin (10-1000 microM) also inhibited the binding of PDGF to BLM preparations dose-dependently. From these results, it is proposed that PDGF stimulates (Ca2+ +Mg2+)-ATPase activity of kidney BLM preparations by enhancing its affinity for free Ca2+ through a specific receptor.