Abstract
The expression of the channels-enzymes TRPM6 and TRPM7 in the human heart remains poorly defined, and TRPM6 is generally considered not to be expressed in cardiomyocytes. We examined their expression at protein and mRNA levels using right atrial samples resected from patients (n = 72) with or without ischemic heart disease (IHD) and samples from all chamber walls of explanted human hearts (n = 9). TRPM6 and TRPM7 proteins were detected using immunofluorescence on isolated cardiomyocytes, ELISA on tissue homogenates, and immunostaining of cardiac tissue, whereas their mRNAs were detected by RT-qPCR. Both TRPM6 and TRPM7 were present in all chamber walls, with TRPM7 being more abundant. TRPM6 was co-expressed with TRPM7. The expression levels were dependent on cell incubation conditions (presence or absence of divalent cations, pH of the extracellular milieu, presence of TRP channel inhibitors 2-aminoethoxydiphenyl-borate and carvacrol). These drugs reduced TRPM7 immunofluorescence but increased that of TRPM6. TRPM6 and TRPM7 expression was increased in tissues from IHD patients. This is the first demonstration of the presence and co-expression of TRPM6 and TRPM7 in cardiomyocytes from all chamber walls of the human heart. The increased TRPM6 and TRPM7 expression in IHD suggests that the chanzymes are involved in the pathophysiology of the disease.
Highlights
The expression of the channels-enzymes TRPM6 and TRPM7 in the human heart remains poorly defined, and TRPM6 is generally considered not to be expressed in cardiomyocytes
We used the immunostaining of TRPM7 and TRPM6 proteins of atrial and ventricular cardiomyocytes, performed 2 h or 12 h after cell isolation
The expression level for either TRPM6 or TRPM7 was higher when cells were fixed after 12 h of cardiomyocyte conservation (Fig. 1c,d; compare filled and unfilled columns, respectively)
Summary
The expression of the channels-enzymes TRPM6 and TRPM7 in the human heart remains poorly defined, and TRPM6 is generally considered not to be expressed in cardiomyocytes We examined their expression at protein and mRNA levels using right atrial samples resected from patients (n = 72) with or without ischemic heart disease (IHD) and samples from all chamber walls of explanted human hearts (n = 9). The expression levels were dependent on cell incubation conditions (presence or absence of divalent cations, pH of the extracellular milieu, presence of TRP channel inhibitors 2-aminoethoxydiphenyl-borate and carvacrol) These drugs reduced TRPM7 immunofluorescence but increased that of TRPM6. The present study used different approaches, including protein detection by immunostaining of isolated cardiomyocytes or of cardiac tissue, protein measurements by ELISA in cardiac homogenates and mRNA detection by real-time quantitative polymerase chain reaction (RT-qPCR), to examine TRPM6 and TRPM7 expression. We report on the modulation of the measured TRPM6 and TRPM7 fluorescence by the ionic composition of the cell incubation medium, by pharmacological drugs and by the pathological condition of ischemic heart disease
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