ATP and PIP2 dependence of the magnesium-inhibited, TRPM7-like cation channel in cardiac myocytes

• Published in: American Journal of Physiology: Cell Physiology 2006-10, Vol.291 (4), p.C627-C635
• Main Authors: Gwanyanya, Asfree, Sipido, Karin R, Vereecke, Johan, Mubagwa, Kanigula
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Adenosine Triphosphate - pharmacology; Adenosine Triphosphate - physiology; Animals; Cations, Divalent - pharmacology; Electric Conductivity; Guinea Pigs; Heart Ventricles; Hydrolysis; Magnesium - pharmacology; Myocytes, Cardiac - metabolism; Patch-Clamp Techniques; Phosphatidylinositol 4,5-Diphosphate - antagonists & inhibitors; Phosphatidylinositol 4,5-Diphosphate - physiology; Phosphoprotein Phosphatases - antagonists & inhibitors; Phosphoric Monoester Hydrolases - antagonists & inhibitors; Protein Kinase Inhibitors - pharmacology; Rats; Swine; Time Factors; TRPM Cation Channels - antagonists & inhibitors; TRPM Cation Channels - drug effects; TRPM Cation Channels - metabolism; TRPM Cation Channels - physiology
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00074.2006

1 Experimental Cardiac Surgery, Heart and Vessel Diseases, 2 Laboratory of Experimental Cardiology, and 3 Laboratory of Physiology, Katholieke Universiteit Leuven, Leuven, Belgium Submitted 16 February 2006 ; accepted in final form 10 May 2006 The Mg 2+ -inhibited cation (MIC) current ( I MIC ) in cardiac myocytes biophysically resembles currents of heterologously expressed transient receptor potential (TRP) channels, particularly TRPM6 and TRPM7, known to be important in Mg 2+ homeostasis. To understand the regulation of MIC channels in cardiac cells, we used the whole cell voltage-clamp technique to investigate the role of intracellular ATP in pig, rat, and guinea pig isolated ventricular myocytes. I MIC , studied in the presence or absence of extracellular divalent cations, was sustained for 50 min after patch rupture in ATP-dialyzed cells, whereas in ATP-depleted cells I MIC exhibited complete rundown. Equimolar substitution of internal ATP by its nonhydrolyzable analog adenosine 5'-( , -imido)triphosphate failed to prevent rundown. In ATP-depleted cells, inhibition of lipid phosphatases by fluoride + vanadate + pyrophosphate prevented I MIC rundown. In contrast, under similar conditions neither the inhibition of protein phosphatases 1, 2A, 2B or of protein tyrosine phosphatase nor the activation of protein kinase A (forskolin, 20 µM) or protein kinase C (phorbol myristate acetate, 100 nM) could prevent rundown. In ATP-loaded cells, depletion of phosphatidylinositol 4,5-bisphosphate (PIP 2 ) by prevention of its resynthesis (10 µM wortmannin or 15 µM phenylarsine oxide) induced rundown of I MIC . Finally, loading ATP-depleted cells with exogenous PIP 2 (10 µM) prevented rundown. These results suggest that PIP 2 , likely generated by ATP-utilizing lipid kinases, is necessary for maintaining cardiac MIC channel activity. cation channels; hydrolysis; phosphoinositides; rundown Address for reprint requests and other correspondence: K. Mubagwa, Experimental Cardiac Surgery, K. U. Leuven, Campus Gasthuisberg, Herestraat 49, B-3000, Leuven, Belgium (e-mail: kanigula.mubagwa{at}med.kuleuven.be )