The effects of alterations in membrane sodium transport on rat aortic smooth muscle proliferation

The univalent cations Na+, K+ and H+ are known to play a critical role in regulating growth in a number of mammalian cell types. In this study we used tissue culture to explore the ways in which two cation transport processes, known to affect the intracellular concentrations of these ions, and Na-H exchange and the Na-K pump, affect serum proliferation of rat aortic smooth muscle. Exposure of quiescent serum-deprived smooth muscle to 10% serum increased both the Na-H exchange and the activity of the Na-K pump. This activation of Na-H exchange increased intracellular pH in proliferating cells by 0.22 units. Attenuation of exchange activity by 40 mumol/l ethylisopropylamiloride (EIPA) reduced the smooth muscle replication rate by 79%. Attenuation of the Na-K pump activity also reduced the replication rate. These results indicate that alterations in the activities of either Na-H exchange or Na-K pump activity will influence smooth muscle cell replication.