Differential Expression Of TRPC Channels In The Left Ventricle Of Spontaneously Hypertensive Rats, Effects Of TRPC Channels On Left Ventricular Systolic Dysfunction

Background Evidence suggests that ion channels mediate the process of capacitative Ca2+ entry into cells, which is essential for longer-term Ca2+ signals and replenishment of Ca2+ stores. Transient Receptor Potential-Canonical (TRPC) channels are mammalian homologs of the Transient Receptor Potential (TRP). Members of the TRPC subfamily are implicated as the Ca2+ entry pathways involved in pulmonary hypertension and essential hypertension, as well as promoting vascular disease in hypertension. Connection between TRPC channels and heart hypertrophy has also been suggested. TRPC proteins have the ability to regulate calcineurin signaling and the hypertrophic growth of the myocardium in vivo, and thus may function as SOCCs. However, the expression of the TRPC channels in the heart has not been clearly described. So, we were to detect the expression of TRPC channels in the left ventricle and to determine whether TRPC expression correlated with either increased blood pressure or left ventricular systolic dysfunction.Objectives This study was designed to identify the differential expression of the canonical transient receptor potential (TRPC) channels in the left ventricle of spontaneously hypertensive rats (SHR).Methods Eight, nine, ten weeks old male SHRs and age-matched WKYs were used in this investigation (n=6 for each group). Echocardiography studies were performed to compare the left ventricular function in SHR versus Wistar-Kyoto rats (WKY), and the mRNA level of the TRPC channels was determined by quantitative real-time RT-PCR (qRT-PCR). Western blots were performed to examine whether the mRNA expression corresponded with the protein expression.Results (1) The HR was higher in the SHR group (p<0.05). The SHR had significantly elevated SBP, DBP and MBP compared to WKY (p<0.01). (2)Compared with WKYs, the ejection fraction (EF) and left ventricular fractional shortening (LVFS) were significantly higher in both the nine-week-old and ten-week-old SHR, while the mFS was significantly lower only in the ten-week-old group. These data demonstrate that the SHRs only had left ventricular systolic dysfunction at 10 weeks of age.Left-ventricular-diastolic-function variables were expressed by the ratio of E-wave and A-wave, but the differences between SHR and WKY were not significantly (p>0.05). (3)Compared with WKYs, the mRNA expression levels of TRPC4 and TRPC5 in the left ventricle were higher in SHRs. But only in the ten-week-old group, the mRNA levels of TRPC4 and TRPC5 were found to be significantly upregulated in the hypertensive heart, in parallel with the ddCt study (p=0.032 for TRPC4 and p=0.043 for TRPC5). Besides, the mRNA levels of TRPC4 and TRPC5 were higher in ten-week-old SHRs versus nine-week-olds but not significant (p=0.67 for TRPC4 and p=0.47 for TRPC5, Table 4), so did the nine-week-old SHRs versus eight-week-olds (p =0.25 for TRPC4 and p=0.79 for RPC5, Table 4) and ten-week-old SHRs versus eight-week-olds (p=0.33 for TRPC4 and p=0.30 for RPC5, Table 4). The differences of the gene expressions between SHRs and their controls (10 weeks of age) were not significant for the other members of the TRPC family (p=0.126 for TRPC1, p=0.507 for TRPC3, p=0.90 for TRPC6 and p=0.058 for TRPC7). (4)On Western blots, we detected TRPC4 and TRPC5 proteins in rat myocardium as single bands migrating both at 97 kDa, their protein levels were found to be upregulated in the hypertensive heart, in parallel with their mRNA expression. (5)The data of ten-week-old SHR was used for analysis of correlation. There was a positive correlation between the mRNA level of TRPC4 and SBP (r=0.728,p=0.017), DBP (r=0.681, p=0.030), and MBP (r=0.711, p=0.021). TRPC5 mRNA levels were positively correlated with SBP (r=0.650, p=0.042) and MBP (r=0.642, p=0.045). The correlation between TRPC4/5 and HR was not significant (p>0.05). TRPC4/5 mRNA level was negatively correlated with mFS (r=-0.844,p=0.002 between TRPC4 and mFS, r=-0.736, p=0.015 between TRPC5 and mFS).Conclusion Our study demonstrated the differential expression of TRPC channels in the left ventricle of spontaneously hypertensive rats. At the initial stage of hypertension, TRPC4 and TRPC5 may be the most important subtypes expressed in the left ventricle of the SHRs and participate in the development of left ventricular systolic dysfunction.