GUANINE-NUCLEOTIDE BINDING-PROTEINS MAY MODULATE GATING OF CALCIUM CHANNELS IN VASCULAR SMOOTH-MUSCLE .1. STUDIES WITH FLUORIDE

  • 1 July 1989
    • journal article
    • research article
    • Vol. 250  (1) , 343-351
Abstract
Fluoride (F-), a known stimulator of G-proteins, was used to examine the relationship between G-proteins and calcium channels (CaC) in rat vascular smooth muscle (VSM). Treatment of isolated rat tail artery helical strips with F- (2.5-20 mM) produced a Ca++-dependent contraction. In the absence of added AlCl3, subthreshold NaF shifted the KCl, as well as the arginine vasopressin and norepinephrine concentration-related tension curves to the left. Nifedipine and verapamil, known CaC blockers, inhibited the NaF-related contraction. AlCl3 (20 .mu.M), which is required for G-protein stimulation by F-, strikingly potentiated the contractile response to F-. The NaF-induced contraction was relaxed by 3-isobutyl-1-methylxanthine as well as by forskolin and by dibutyryladenosine-cyclic AMP, and the effect therefore may be independent of cAMP. 45Ca-uptake was elevated by NaF, and partially blocked by nifedipine and verapamil. NaF also inhibited the basal and forskolin-stimulated cAMP production, suggesting that F- stimulated the putative Gi in the intact VSM cells. NaF stimulated accumulation of IP in a concentration-dependent manner, indicating that F- stimulated the putative G-protein Gp which couples various receptors to hydrolysis of phosphoinositides and mobilization of Ca++. These results indicate that NaF-induced vasoconstriction is related to the opening of the CaC in the plasma membrane and perhaps a subsequent entry of the extra cellular Ca++ into the cell. The present studies suggest that F- has the ability to stimulate at least two putative G-proteins in rat tail artery smooth muscle cells, inhibitory G-protein and/or Gp, and that their activation may mediate the gating of CaC by a cAMP-independent mechanisms in rat VSM.

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