Pressure‐Induced Constriction of the Middle Cerebral Artery is Abolished in TrpC6 Knockout Mice

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Pressure‐induced constriction (PIC) is an inherent response of small arteries and arterioles in which increases in intraluminal pressure evoke vasoconstriction. It is a critical mechanism of blood flow autoregulation in the kidney and brain. Degenerin (Deg) and transient receptor potential (Trp) protein families have been implicated in transduction of PIC because of evolutionary links to mechanosensing in the nematode and fly. We hypothesize that Deg and Trp proteins associate to form a multi‐meric mechanosensing complex in vascular smooth muscle cells (VSMCs), in which Deg and Trp proteins play different, yet equally critical, roles as sensors and amplifiers, in PIC molecular signaling. Our laboratory has provided direct evidence that the Deg protein bENaC acts as a sensor by mediating mechanoreceptor currents in isolated VSMCs. While TrpC6 has been suggested to mediate PIC, direct supporting evidence is lacking. Therefore, the aim of this study was to determine the importance of TrpC6 in PIC signaling using a mouse model lacking TrpC6. To address this aim, we evaluated graded pressure (20–90 mm Hg), depolarization‐ (20–80 mM KCl) and adrenergic receptor‐(phenylephrine, PE 10−7–10−4 M) mediated constriction of isolated middle cerebral artery (MCA) segments from 9 weeks old male wild‐type (+/+, n=7) and homozygous null (−/−, n=9) TrpC6 mice (Jackson Laboratories). Isolated MCA segments were cannulated and pressurized with physiological salt solution using pressure myography (Living Systems). The data were analyzed preliminarily using independent 2‐tailed t‐test. Normalized MCA vasoconstrictor responses to KCl (80 mM, 45.5±1.1% vs 40.9±1.2%, p=0.2) and PE (10−4 M, 37.4±1.7% vs 38.7.0±1.2%, p=0.8) were similar in TrpC6−/− and TrpC6+/+ mice, respectively. In contrast, PIC responses were totally abolished in TrpC6 −/− mice; at 90 mmHg calculated myogenic tone was 0.8±0.5% vs 10.7±1.7%, p=0.0002, in TrpC6−/− and TrpC6+/+ mice, respectively. Additionally, there were no changes in mechanical properties of circumferential wall strain (0.2±0.02 vs. 0.2±0.02, p=0.8) and stress (2.7±0.1 vs. 3.1±0.4, p=0.4), at 90 mmHg; or morphological properties wall thickness (13.4±0.8μm vs. 14.3±1.5μm, p=0.6) and wall‐to‐lumen ratio (0.3±0.02 vs. 0.3±0.04, p=0.7), at 50 mmHg between TrpC6−/− and TrpC6+/+ mice. Although these results suggest that TrpC6 is required for the PIC response, they do not identify the role of TrpC6. Studies in the nematode suggest that Deg and Trp channels play different, yet equally critical roles in mechano‐signaling; Deg channels mediate mechanoreceptor currents, while Trp channels mediate post‐transduction signal amplification. Future studies will determine the role of TrpC6 in isolated VSMCs and cerebral blood flow autoregulation. This research was supported by P20GM104357, P20121334, P01HL051971, R01HL1136684.Support or Funding InformationP20GM104357, P20121334, P01HL051971, R01HL1136684.