Background: Activation of the intracrine renin angiotensin systems (RAS) is increasingly recognized as contributing to human pathologies, yet non-canonical renin-independent mechanisms for angiotensin II (Ang II) biosynthesis remain controversial. Direct Ang II generation from angiotensin-(1–12) [Ang-(1–12)] by chymase is an essential intracrine source for regulation of cardiac function. Using a transgenic rat model that overexpresses the human angiotensinogen gene [TGR(hAGT)L1623] and displays increased cardiac Ang II levels, this study aimed to provide evidence for intracrine activation of L-type calcium currents (ICa-L) mediated by the Ang-(1–12)/chymase axis. Methods and results: On patch clamp, ICa-L density was significantly higher in TGR(hAGT)L1623 (−6.4 ± 0.3 pA/pF) compared to Sprague Dawley (SD) cardiomyocytes (−4.8, ± 0.5 pA/pF). Intracellular administration of Ang II and Ang-(1–12) elicited a ICa-L increase in both SD and TGR(hAGT)L1623 cardiomyocytes, albeit blunted in transgenic cells. ICa-L activation by intracellular Ang II and Ang-(1–12) was abolished by the specific Ang II type 1 receptor blocker E−3174. Co-administration of a chymase inhibitor prevented activation of ICa-L by Ang-(1–12). Confocal micrographs revealed abundant chymase (mast cell protease 5) immunoreactive protein in SD and TGR(hAGT)L1623 cardiomyocytes. Conclusions: Our data demonstrate the existence in cardiomyocytes of a calcium channel modulatory activity responsive to Ang II generated by the Ang-(1–12)/chymase axis that signals via intracellular receptors. Chronically elevated Ang II in TGR(hAGT)L1623 hearts leading to increased intracellular calcium through ICa-L suggests that activation of this Ang-(1–12)/chymase-governed cardiac intracrine RAS may contribute to the pathological phenotypes observed in the humanized model of chronic hypertension and cardiac hypertrophy.
