Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Physiology and Pharmacology

Supervisor

Welsh, Donald G.

Abstract

The myogenic response refers to the intrinsic ability of arteries to constrict to elevated pressure, developing “tone”. The underlying mechanism has yet to be elucidated but recent evidence suggests that the angiotensin II type 1 receptor (AT1R) is a key mechanosensor, linking intravascular pressure to tone development. One intriguing aspect of this receptor is its ability to activate NADPH oxidase (Nox), an enzyme responsible for the production of reactive oxygen species (ROS). The goal of this study was to ascertain the role of Nox in myogenic tone development. Isolated rat cerebral arteries were mounted in a myograph, pressurized to 60mmHg and diameter measured prior to and following the application of apocynin (a general Nox inhibitor) or ML-171 (a Nox1 specific inhibitor). Pressure-induced constriction was attenuated by apocynin or ML-171 in a concentration dependent manner. This response to ML-171 was attenuated in the presence of paxilline (1 µM) or Ni2+ (50 µM), inhibitors of the large-conductance Ca2+-activated potassium (BKCa) channel and the T-type Ca2+ channel CaV3.2, respectively. Control experiments showed no discernable role for Nox2. Subsequent immunohistochemistry confirmed the presence of CaV3.2 and Nox1 in isolated smooth muscle cells, and proximity ligation assay showed the two proteins co-localized within 40nm in the cell membrane. These findings indicate rat arterial Nox1 may regulate the myogenic response by moderating a key negative feedback pathway linked to CaV3.2. This work sheds new light on mechanosensation and how unique signaling proteins impact the ability of resistance arteries to respond to intravascular pressure.

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