NA+ H+ EXCHANGE IN VASCULAR SMOOTH-MUSCLE CELLS IS CONTROLLED BY GTP-BINDING PROTEINS/

This study examines the involvement of GTP-binding proteins (Gps) in t he regulation of Na+/H+ exchange and Ca2+ influx, which are increased in vascular smooth muscle cells from spontaneously hypertensive rats, Gp activity was modulated by fluoride, GTP gamma S, GDP beta S, and an tisense oligodeoxynucleotides complementary to conserved regions of th e alpha- and beta-subunits of Gps (alpha-comm and beta-comm, respectiv ely). beta-Adrenergic-induced G(5)-mediated cAMP production was used a s a positive control to estimate the efficiency of these compounds. Na +/H+ exchange, measured as ethylisopropyl amiloride-sensitive Na-22 in flux, was activated by 5- to 6-fold by a 30-minute preincubation of ce lls with 10 mmol/L NaF with a K-0.5 for NaF of similar to 13 mmol/L, I n contrast, no activation of Ca-45 influx was observed under preincuba tion of vascular smooth muscle cells with NaF in Ca2+-free medium, whe reas at [Ca2+](o) >0.5 mmol/L, simultaneous addition of Ca-45 and 10 m mol/L NaF led to sharply increased isotope uptake. NaF-induced Ca-45 i nflux did not reach saturation up to 3 mmol/L [Ca2+](o) and 20 mmol/L NaF and was correlated with the formation of calcium-fluoride complexe s measured by light scattering. GTP gamma S increased basal cAMP produ ction and Na+/H+ exchange, whereas GDP beta S decreased isoproterenol- induced cAMP production and Na+/H+ exchange, alpha-comm reduced wherea s beta-comm augmented isoproterenol-induced cAMP production by 70%. Bo th oligodeoxynucleotides decreased basal Na+/H+ exchange by 40% to 50% . NaF-induced Na+/H+ exchange was not sensitive to alpha-comm but was inhibited by 60% in beta-comm-loaded cells. Neither basal nor NaF-indu ced Ca-45 uptake was affected by GTP gamma S, GDP beta S, and the olig odeoxynucleotides. Our results show that Ca-45 uptake is activated by NaF in vascular smooth muscle cells by nonspecific accumulation of cal cium-fluoride complexes and is not related to modification of Gps. On the contrary, the Na+/H+ exchanger is controlled by Gps, and Gp beta-s ubunits are involved in [Ca2+](o)-independent activation of this carri er by NaF.