Background:This study characterized the cardiac telocyte (TC) population both in vivo and in vitro,and investigated its telomerase activity related to mitosis.Methods:Using transmission electron microscopy and a phase contrast microscope,the typical morphological features of cardiac TCs were observed;by targeting the cell surface proteins CD 1 17 and CD34,CD 117+CD34+ cardiac TCs were sorted via flow cytometry and validated by immunofluorescence based on the primary cell culture.Then the optimized basal nutrient medium for selected population was examined with the cell counting kit 8.Under this conditioned medium,the process of cell division was captured,and the telomerase activity ofCD 117+CD34+ cardiac TCs was detected in comparison with bone mesenchymal stem cells (BMSCs),cardiac fibroblasts (CFBs),cardiomyocytes (CMs).Results:Cardiac TCs projected characteristic telopodes with thin segments (podomers) in altation with dilation (podoms).In addition,64％ of the primary cultured cardiac TCs were composed of CD 117+CD34+ cardiac TCs;which was verified by immunofluorescence.In a live cell imaging system,CD 117+CD34+ cardiac TCs were observed to enter into cell division in a short time,followed by an significant invagination forming across the middle of the cell body.Using a real-time quantitative telomeric-repeat amplification assay,the telomerase concentration in CD117+CD34+ cardiac TCs was obviously lower than in BMSCs and CFBs,and significantly higher than in CMs.Conclusions:Cardiac TCs represent a unique cell population and CD117+CD34+ cardiac TCs have relative low telomerase activity that differs from BMSCs,CFBs and CMs and thus they might play an important role in maintaining cardiac homeostasis.