IONIC MECHANISMS REGULATING SODIUM ENTRY INTO VASCULAR SMOOTH-MUSCLE

1. Na+/H+ exchange, an ethylisopropylamiloride (EIPA)-sensitive Na+ and HCO3- dependent system and a diisothio-cyanatostilbenedisulphonic acid (DIDS)-sensitive Na+ and HCO3- transporter, contribute to sodium influx and intracellular pH (pH(i)) regulation in vascular smooth muscle. 2. In cultured cells from the human internal mammary artery, Na+/H+ exchange and the EIPA-sensitive Na+ and HCO3- dependent system contribute about 80% to basal sodium influx. The residual Na+ influx is both EIPA and DIDS-insensitive. 3. Sodium influx via these mechanisms influences the ability of vascular smooth muscle to synthesize protein late in the G1 phase of the mitotic cell cycle. This, in turn, affects DNA biosysthesis. 4. These Na+ exchanges/transporters have the capability to facilitate the development of vascular hypertrophy in hypertension.