The Angiotensin II Type 1b Receptor is Sufficient for Sensing Intraluminal Pressure in Cerebral Artery Smooth Muscle Cells
Authors: Pires Paulo Wagner , Ko Eun‐A , Earley Scott 
Published: November 2023

Autoregulation of cerebral blood flow relies on the ability of vascular smooth muscle cells (SMC) to respond to changes in intraluminal pressure through myogenic constriction. Increased stress at the vascular wall is detected by a force‐sensitive signaling network in SMC that activates a PLCγ1‐depedent signaling pathway leading to an increase in depolarizing transient inward cation currents (TICCs) mediated by transient receptor potential melastatin 4 (TRPM4) channels. The molecular identity of the primary mechanosensor in cerebral SMC has not been conclusively identified. Based on previous studies suggesting that angiotensin II type 1 receptors (AT1R) are inherently mechanosensitive in other vascular beds, we hypothesized that the receptor plays a similar role in cerebral artery SMC acting upstream of TRPM4 channels. In amphotericin B perforated patch‐clamp electrophysiology experiments using cerebral pial artery SMC freshly isolated from C57BL/6 mice, TICCs were activated by angiotensin II (Ang II) (30 nM, NPo = 0.18±0.06 vs 1.59±0.28, baseline vs Ang II, n=7) or application of negative pressure (−20 mmHg, NPo = 0.17±0.08 vs 1.04±0.22, baseline vs stretch, n=14) to the recording electrode to stretch the plasma membrane, and this response was blocked by the selective AT1R inhibitor losartan (NPo: 1.04±0.22 vs 0.20±0.09, stretch vs stretch+losartan, n=5). Losartan also blunted myogenic tone of distal branches of the posterior cerebral artery (PCA) in pressure myograph experiments (14.4±2.3 vs 6.1±2.1 %tone at 100 mmHg, vehicle vs losartan, p<0.05, n=6). These data are consistent with our hypothesis and suggest that AT1R acting upstream of TRPM4 channels is necessary for myogenic constriction of cerebral arteries. Rodents express two closely related AT1R subtypes: AT1Ra and AT1Rb. No differences in stretch‐induced (−20 mmHg) TICC activity were observed between cerebral artery SMC from AT1Ra−/− and wild type (WT) mice (NPo: 0.99±0.19 vs 1.04±0.22, AT1Ra−/− vs WT, n=20 and n=14), and, unexpectedly, PCAs from AT1Ra−/− mice showed increased myogenic constriction compared to WT (10.9±2.1 vs 20.2±3.1, WT vs AT1Ra−/−, n=6, p<0.05). However, losartan diminished stretch‐induced TICC activity (NPo = 0.12±0.04, n=5) and reduced myogenic constriction of PCA from AT1Ra−/− mice (4.2±1.5%, n=5, p<0.05 vs AT1Ra−/−). These data indicate that a losartan sensitive receptor, most likely AT1Rb, is necessary for sensing pressure in cerebral artery SMC in the absence of AT1Ra. Furthermore, Ang II (30 nM) increased TICC activity in cerebral artery SMC (NPo=0.80±0.10, n=7) and constricted PCA from AT1Ra−/− and WT mice to a similar degree (%vasoconstriction: 12.1±2.4 vs 10.4±2.6, WT vs AT1Ra−/−, n=4), suggesting that AT1Rb can maintain agonist dependent responses in the absence of AT1Ra. In conclusion, our data demonstrate that in murine cerebral artery SMC AT1R coupled to TRPM4 induces depolarizing currents in response to stretch of the plasma membrane that lead to myogenic constriction. Activity of the AT1Rb−/− subtype alone is sufficient to maintain myogenic and agonist‐induced constriction of cerebral arteries. All data are mean±SEM.

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R01HL091905 (SE), 15POST2472002 (PWP).