Downregulation of AT2R decreases the responsiveness of BKCa channels to angiotensin II in patients with hypertension

Angiotensin II (Ang II) modulates blood pressure via Ang II type 1 receptor (AT1R) and type 2 receptor (AT2R). The activation of AT2R relaxes vascular tone through opening large-conductance Ca2+-activated potassium (BKCa) channels in vascular smooth muscle cells (SMCs). In the present study, we studied the role of the AT2R-BKCa pathway in patients with hypertension. The mesenteric arterial SMCs (MSMCs) were obtained from normotensive patients (NP) and hypertensive patients (HP). BKCa currents were recorded with patch clamp and the expressions of mRNAs and proteins of AT1R/AT2R were analyzed by RT-PCR and Western blotting, respectively. Ang II significantly increased the macroscopic BKCa currents at the whole cell level, while increased the open probability and decreased the mean close time of BKCa channels at the single channel level with AT1R blockade by valsartan in NP. However, Ang II had no effect on the BKCa currents at the same condition in HP. Furthermore, the expressions of mRNA and protein of AT2R but not AT1R were markedly decreased in the MSMCs of HP compared to that of NP. The data suggest that AT2R is well functioned in the MSMCs in NP but not in HP and deficiency in the AT2R-BKCa pathway may contribute to the development of hypertension.