Master of Science
Physiology and Pharmacology
Welsh, Donald G.
In cerebral arteries, inwardly rectifying potassium channels (KIR) contribute to smooth muscle hyperpolarization to control arterial diameter and tone. Emerging evidence highlighted their regulation by pressure, though the underlying mechanism remains unclear. This thesis explored this concept through examination of KIR channels in mouse and rat cerebral vascular smooth muscle (VSM). Experiments progressed from isolated cells to whole animals, employing electrophysiology, immunocytochemistry, proximity ligation assay, and arterial spin-labelling MRI techniques. Initial experiments indicated that KIR activity persists beyond KIR2.1 knockout in smooth muscle, clarifying their molecular composition. Our subsequent study identified key structural components involved in KIR mechanosensing. Disruption of the cytoskeleton impaired the KIR pressure response in isolated cells. Syntrophin and caveolin-1, protein intermediates known to facilitate actin-channel interactions, were both identified in VSM cells and found co-localized with KIR2.2. In summary, this thesis provides insight into the composition, function, and associated mechanotransduction complex of KIR channels in VSM.
Summary for Lay Audience
Blood is supplied to the brain through a network of resistance arteries that continually adjust their diameter to maintain constant flow. They achieve this through a layer of smooth muscle which contracts and relaxes to constrict or dilate the vessel. Ion channels control the contractile state (tone) of vascular smooth muscle by changing their activity in response to external forces such as pressure. Inwardly rectifying potassium channels (KIR) are among these channels and have recently been found to respond to pressure, although it is unclear how this occurs. This project improved our understanding of how vessels sense pressure by studying KIR channels in the smooth muscle of cerebral arteries. Our first study utilized a genetic knockout mouse model to investigate both the role and molecular composition of vascular KIR channels. Through these experiments, we determined which specific subtypes of KIR channels were functionally relevant in smooth muscle cells. Our second study sought to uncover the mechanism that KIR channels utilize to sense changes in pressure. We found that KIR pressure sensitivity was dependent on interactions with several structural proteins within the cell. By identifying these components, our work provides new targets to investigate in disease states where arterial tone is disrupted such as hypertension and metabolic syndrome. To summarize, the conclusions drawn from this study improve our knowledge of the mechanisms arteries use to translate physical stimuli into diameter changes.
Fletcher, Jacob, "Inwardly Rectifying Potassium Channels: Regulators of Myogenic Tone in Cerebrovascular Smooth Muscle" (2021). Electronic Thesis and Dissertation Repository. 7708.