Platelet-derived growth factor causes sustained depletion of both inositol trisphosphate-sensitive and caffeine-sensitive intracellular calcium stores in vascular smooth muscle cells.
Since the platelet-derived growth factor (PDGF)-induced increase in cellular inositol 1,4,5-trisphosphate (InsP3) has been found to decay to basal levels soon after the onset of PDGF exposure, it has been argued that activation of Ca2+ release from intracellular stores must be similarly transient. The possibility remains, however, that PDGF-induced release of stored Ca2+ is initiated and sustained by other second-messenger systems. To test the hypothesis that PDGF-BB initiates sustained Ca2+ release from cellular stores, we performed 4-hour 45Ca effluxes on monolayers of A7r5 vascular smooth muscle cells in small, continuously perfused chambers. Isoform PDGF-BB (5 ng/mL for 30 minutes or 30 ng/mL for 15 minutes) was added to the perfusate beginning at 30 minutes of efflux. A dose-related increase in 45Ca release was sustained as long as PDGF-BB was present. Detailed kinetic analysis and nonlinear least-squares fitting of the experimental data revealed that (1) PDGF-BB induced sustained increases of 2.86-fold (5 ng/mL) and 6.50-fold (30 ng/mL) in the rate constant governing Ca2+ release from intracellular stores, (2) the apparent Km for this effect was 13.4 +/- 1.31 ng PDGF-BB/mL, and (3) the entire agonist-releasable Ca2+ store (presumably sarcoplasmic reticulum) is sensitive to PDGF-BB. These data indicate that PDGF-BB causes a sustained depletion of intracellular Ca2+ stores by means of sustained activation of Ca2+ release and suggest that intraorganellar Ca2+ may be one of the signals that mediates long-term smooth muscle responses to PDGF.
Lapidot
S A
SA
Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Phair
R D
RD
D000818:Animals; D000077214:Becaplermin; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D007295:Inositol Phosphates / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D008954:Models, Biological; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D020574:Proto-Oncogene Proteins c-sis; D015290:Second Messenger Systems; D015398:Signal Transduction
D007295:Inositol Phosphates; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D000077214:Becaplermin; D002110:Caffeine; D002118:Calcium