Copyright © 2006, European Society of Cardiology
Phospholipase C-dependent control of cardiac calcium homeostasis involves a TRPC3-NCX1 signaling complex
aInstitute of Pharmaceutical Sciences, Pharmacology and Toxicology, Karl-Franzens-University, Graz, Austria
bInstitute of Molecular Biosciences, Karl-Franzens-University, Graz, Austria
cInstitute of Biophysics, University of Linz, Austria
* Corresponding author. Institute of Pharmaceutical Sciences, Pharmacology and Toxicology, Universitaetsplatz 2, 8010 Graz, Austria. Tel.: +43 316 380 5570; fax: +43 316 380 9890. Email address: klaus.groschner{at}uni-graz.at
Objective: Members of the classical transient receptor potential protein (TRPC) family are considered as key components of phospholipase C (PLC)-dependent Ca2+ signaling. Previous results obtained in the HEK 293 expression system suggested a physical and functional coupling of TRPC3 to the cardiac-type Na+/Ca2+ exchanger, NCX1 (sodium calcium exchanger 1). This study was designed to test for expression of TRPC3 (transient receptor potential channel 3) and for the existence of a native TRPC3/NCX1 signaling complex in rat cardiac myocytes.
Methods: Protein expression and cellular distribution were determined by Western blot and immunocytochemistry. Protein–protein interactions were investigated by reciprocal co-immunoprecipitation and glutathione S-transferase (GST)-pulldown experiments. Recruitment of protein complexes into the plasma membrane was assayed by surface biotinylation. The functional role of TRPC3 was investigated by fluorimetric recording of angiotensin II-induced calcium signals employing a dominant negative knockdown strategy.
Results: TRPC3 immunoreactivity was observed in surface plasma membrane regions and in an intracellular membrane system. Co-immunolabeling of TRPC3 and NCX1 indicated significant co-localization of the two proteins. Both co-immunoprecipitation and GST-pulldown experiments demonstrated association of TRPC3 with NCX1. PLC stimulation was found to trigger NCX-mediated Ca2+ entry, which was dependent on TRPC3-mediated Na+ loading of myocytes. This NCX-mediated Ca2+ signaling was significantly suppressed by expression of a dominant negative fragment of TRPC3. PLC stimulation was associated with increased membrane presentation of both TRPC3 and NCX1.
Conclusion: These results suggest a PLC-dependent recruitment of a TRPC3-NCX1 complex into the plasma membrane as a pivotal mechanism for the control of cardiac Ca2+ homeostasis.
KEYWORDS Transient receptor potential protein; TRPC3; Na/Ca-exchanger; Cardiac myocytes; Calcium signaling
Time for primary review 18 days
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