ACTIVATION OF Na+/H+ EXCHANGE IS UNNECESSARY IN THE INDUCTION OF c‐fos mRNA IN SERUM‐STIMULATED VASCULAR SMOOTH MUSCLE CELLS

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Abstract
SUMMARY: 1. The effects of extracellular Na+ concentration ([Na+]o) on serum‐stimulated c‐fos mRNA induction in vascular smooth muscle cells (VSMC) were studied to examine whether the activation of Na+/H+ exchange and the following intracellular alkalinization are necessary in the induction of c‐fos in VSMC.2. When monitored with 2′, 7′‐bis (carboxylethyl)‐5(6)‐carboxyfluorescein, the reduction in [Na+]o in HCO3−‐free buffer caused a dose‐dependent inhibition of Na+‐dependent intracellular pH recovery in acid‐loaded VSMC. In addition, serum‐stimulated intracellular alkalinization in VSMC was completely blocked by the removal of extracellular Na+.3. By contrast, c‐fos induction, quantified by slit blot hybridization of c‐fos mRNA, was not fully inhibited by the reduction of [Na+]o. Furthermore, amiloride and ethylisopropyl‐amiloride, inhibitors of Na+/H+ exchange, only partially blocked c‐fos induction by serum.4. We concluded from the observation above, that the intracellular alkalinization caused by the activation of Na+/H+ exchange was unnecessary in serum‐stimulated induction of c‐fos mRNA in VSMC.