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(Hypertension. 1998;31:259.)
© 1998 American Heart Association, Inc.

Scientific Contributions

Na⁺/H⁺ Exchange in Vascular Smooth Muscle Cells Is Controlled by GTP-Binding Proteins

Sergei N. Orlov; Sergei L. Aksentsev; Nickolai I. Pokudin; Johanne Tremblay; Pavel Hamet

From the Research Center, Centre Hospitalier Universitaire de Montréal-(CHUM), Montreal, Quebec, Canada (S.N.O., J.T., P.H.), and the Laboratory of Biomembranes, Faculty of Biology, Moscow State University, Moscow, Russia (S.N.O., S.L.A., N.I.P.)

Correspondence to Pavel Hamet, Research Center, CHUM, Pavillon Hôtel-Dieu, Laboratory of Molecular Medicine, 3850 St. Urbain St., Montréal, Québec H2W 1T8, Canada. E-mail hamet{at}ere.umontreal.ca

This study examines the involvement of GTP-binding proteins (Gps) in the 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, GTPS, GDPßS, and antisense oligodeoxynucleotides complementary to conserved regions of the - and ß-subunits of Gps (-comm and ß-comm, respectively). ß-Adrenergic-induced G_s-mediated cAMP production was used as a positive control to estimate the efficiency of these compounds. Na⁺/H⁺ exchange, measured as ethylisopropyl amiloride-sensitive ²²Na influx, was activated by 5- to 6-fold by a 30-minute preincubation of cells with 10 mmol/L NaF with a K_0.5 for NaF of _13 mmol/L. In contrast, no activation of ⁴⁵Ca influx was observed under preincubation of vascular smooth muscle cells with NaF in Ca²⁺ -free medium, whereas at [Ca²⁺]_o>0.5 mmol/L, simultaneous addition of ⁴⁵Ca and 10 mmol/L NaF led to sharply increased isotope uptake. NaF-induced ⁴⁵Ca influx did not reach saturation up to 3 mmol/L [Ca²⁺]₀ and 20 mmol/L NaF and was correlated with the formation of calcium-fluoride complexes measured by light scattering. GTPS increased basal cAMP production and Na⁺/H⁺ exchange, whereas GDPßS decreased isoproterenol-induced cAMP production and Na⁺/H⁺ exchange, -comm reduced whereas ß-comm augmented isoproterenol-induced cAMP production by 70%. Both oligodeoxynucleotides decreased basal Na⁺/H⁺ exchange by 40% to 50%. NaF-induced Na⁺/H⁺ exchange was not sensitive to -comm but was inhibited by 60% in ß-comm-loaded cells. Neither basal nor NaF-induced ⁴⁵Ca uptake was affected by GTPS, GDPßS, and the oligodeoxynucleotides. Our results show that ⁴⁵Ca uptake is activated by NaF in vascular smooth muscle cells by nonspecific accumulation of calcium-fluoride complexes and is not related to modification of Gps. On the contrary, the Na⁺/H⁺ exchanger is controlled by Gps, and Gp ß-subunits are involved in [Ca²⁺]₀-independent activation of this carrier by NaF.

Key Words: vascular smooth muscle cells • Na⁺/II⁺ exchange • Ca²⁺ uptake • fluoride • antisense oligodeoxynucleotides • GTP-binding proteins

Abbreviations: -comm, ß-comm = antisense oligodeoxynucleotides complementary to the conserved part of DNA encoding - and ß-subunits of GTP-binding proteins • DMEM = Dulbecco’s modified Eagle’s medium • EIPA = ethylisopropyl amiloride • Gp = GTP-binding protein • LDH = lactate dehydrogenase • NHE-1 = ubiquitous form of Na⁺/H⁺ • ODN = oligodeoxynucleotides • SHR = spontaneously hypertensive rat • VSMC = vascular smooth muscle cells