Inhibition of the magnesium-sensitive TRPM7-like channel in cardiac myocytes by nonhydrolysable GTP analogs: involvement of phosphoinositide metabolism.

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.