Platelet-derived growth factor regulates K-Cl cotransport in vascular smooth muscle cells

Platelet-derived growth factor (PDGF), apotent serum mitogen for vascular smooth muscle cells (VSMCs), plays animportant role in membrane transport regulation and in atherosclerosis. K-Cl cotransport (K-Cl COT/KCC), the coupled-movement of K and Cl, isinvolved in ion homeostasis. VSMCs possess K-Cl COT activity and theKCC1 and KCC3 isoforms. Here, we report on the effect of PDGF on K-ClCOT activity and mRNA expression in primary cultures of rat VSMCs. K-ClCOT was determined as the Cl-dependent Rb influx and mRNA expression bysemiquantitative RT-PCR. Twenty four-hour serum deprivation inhibitedbasal K-Cl COT activity. Addition of PDGF increased total proteincontent and K-Cl COT activity in a time-dependent manner. PDGFactivated K-Cl COT in a dose-dependent manner, both acutely (10 min)and chronically (12 h). AG-1296, a selective inhibitor of the PDGFreceptor tyrosine kinase, abolished these effects. Actinomycin D andcycloheximide had no effect on the acute PDGF activation of K-Cl COT,suggesting posttranslational regulation by the drug. Furthermore, PDGFincreased KCC1 and decreased KCC3 mRNA expression in a time-dependentmanner. These results indicate that chronic activation of K-Cl COTactivity by PDGF may involve regulation of the two KCC mRNA isoforms,with KCC1 playing a dominant role in the mechanism of PDGF-mediated activation.