Inhibition of the Magnesium-Sensitive TRPM7-like Channel in Cardiac Myocytes by Nonhydrolysable GTP Analogs: Involvement of Phosphoinositide Metabolism

Abstract

BACKGROUND/AIMS: A magnesium-inhibited, transient receptor potential melastatin 7 (TRPM7)-like channel is expressed in cardiac cell membranes. The role and regulation of this channel by intracellular nucleotides and membrane components remain unclear. METHODS: We used the whole-cell voltage-clamp technique in pig isolated ventricular myocytes to investigate the effect of non-hydrolysable guanine nucleotides. RESULTS: The TRPM7-like current, induced by intracellular dialysis with low [Mg(2+)], remained stable when the intracellular solution contained GTP. Substituting GTP by GTP-gamma-S or Gp-pNp, but not GDP-beta-S, induced a run-down of the current. Under dialysis with GTP-gamma-S, inhibiting phospholipase C by edelfosine or intracellularly adding exogenous phosphatidylinositol-4,5-bisphosphate (PIP(2)) decreased run-down, whereas extracellularly applying carbachol and phenylephrine accelerated it. Pretreatment of cells with pertussis toxin did not prevent the run-down induced by GTP-gamma-S. CONCLUSION: Guanine nucleotides can modulate cardiac TRPM7-like channels via a mechanism linked to G proteins and to PIP(2) metabolism.