Background
Localization of neurokinin 1 receptor (NK1R), the endogenous receptor for neuropeptide substance P (SP), has already been described for the right atrium (RA) of the heart. However, the biological role of SP/NK1R signal pathways in the RA remains unclear. Sprague-Dawley rats were randomly divided into 4 groups (n = 22 each); subjected to sham, ischemia/reperfusion-injury (I/R), I/R with 5 nmole/kg SP injection (SP + I/R), and SP + I/R with 1 mg/kg RP67580 injection (RP, a selective non-peptide tachykinin NK1R antagonist) (RP/SP + I/R). The left anterior descending coronary artery was occluded for 40 min followed by 1 day reperfusion with SP or SP + RP or without either. After 1 day, both atria and ventricles as well as the heart apexes were collected.
Conclusion
SP/NK1R might play a role as a key mediator involved in the cellular response to c-Kit+ CPC expansion in RA of the heart within 24 h after I/R.
Results
SP promoted the expression of c-Kit, GATA4, Oct4, Nanog, and Sox2 in only the RA of the SP + I/R rats via NK1R activation. In agreement with these observations, NK1R-expressing c-Kit+ Nkx2.5+GATA4+ cardiac progenitor cells (CPCs) in the ex vivo RA explant outgrowth assay markedly migrated out from RA1 day SP + I/R approximately 2-fold increase more than RA1 day I/R. Treatment of SP promoted proliferation, migration, cardiosphere formation, and potential to differentiate into cardiomyocytes. Using RP inhibitor, NK1R antagonist not only inhibited cell proliferation and migration but also reduced the formation of cardiosphere and differentiation of c-Kit+ CPCs.