UVM Theses and Dissertations
Format:
Print
Author:
Hannah, Rachael Mary
Dept./Program:
Anatomy and Neurobiology
Year:
2010
Degree:
PhD
Abstract:
Cerebral arteries and arterioles supply nutrients and oxygen to meet the metabolic demands of neurons and astrocytes. Cerebral arterioles within the brain (parenchymal arterioles) are in a unique environment (encased by astrocytic processes and lack extrinsic innervation). Parenchymal arterioles are lined by a single layer of endothelial cells. which are surrounded by a single layer of smooth muscle cells. In other types of arteries, the diameter, and hence blood flow, is regulated by K channels in endothelial and smooth muscle cells, with activa, tion of K⁺ channels causing vasodilation and an increase in blood flow. However, little is known about the properties and physiological roles of K⁺ channels in parenchymal arterioles.
The overall hypothesis is that K channels in the endothelial and smooth muscle cells regulate the diameter of parenchymal arterioles. Specifically, I tested the hypotheses that small conductance (SKca) and intermediate conductance (IKca), calcium-sensitive K⁺ channels in endothelium regulate parenchymal arteriolar diameter, and that smooth muscle voltage-gated K⁺ channels (Kv), smooth muscle inwardly-rectifying K⁺ channels (Kjr), and large-conductance, Ca²⁺-sensitive K⁺ channels (BKca) also have distinct roles in the regulation of parenchymal arteriolar diameter.
K currents were measured in isolated endothelial and smooth muscle cells from parenchymal arterioles from rat brain, using the conventional whole cell patch clamp technique. IKca and SKca channels contribute almost the entire K⁺ current in endothelial cells, and BKca and Kv currents were not observed. Smooth muscle cells have prominent BKca, Kjr and Kv channel currents, without any evidence for IKca and SKca currents. Therefore, endothelial and smooth muscle cells exhibit a differential expression of K⁺ channels.
Selective blockers of SKca and IKca channels (apamin and charybdotoxin) constricted pressurized (40 mmHg) parenchymal arterioles by ~16 % and ~16 %, respectively. In contrast, blocking BKca channels with the selective inhibitor, paxilline. caused only modest (6 %) vasoconstriction. The Kv channel blocker, 4-aminopyridine constricted pressurized parenchymal arterioles by ~25 %. These results indicate that endothelial cell IKca and SKca channels as well as smooth Kv channels have an important role in opposing pressure-induced vasoconstriction. Smooth muscle BKca channels contribute to a lesser extent.
These data support the concept that modulation of K channels in endothelial and smooth muscle cells strongly affects the diameter of parenchymal arterioles. Specifically, activation of either endothelial celllKca channels or smooth muscle Kjr channels causes profound vasodilation, and as such represent potential therapeutic targets to increase blood perfusion in the brain. Conversely, a defect in IKca, SKca, or Kv channel function would lead to vasoconstriction, and thereby compromise cortical cerebral blood flow.
The overall hypothesis is that K channels in the endothelial and smooth muscle cells regulate the diameter of parenchymal arterioles. Specifically, I tested the hypotheses that small conductance (SKca) and intermediate conductance (IKca), calcium-sensitive K⁺ channels in endothelium regulate parenchymal arteriolar diameter, and that smooth muscle voltage-gated K⁺ channels (Kv), smooth muscle inwardly-rectifying K⁺ channels (Kjr), and large-conductance, Ca²⁺-sensitive K⁺ channels (BKca) also have distinct roles in the regulation of parenchymal arteriolar diameter.
K currents were measured in isolated endothelial and smooth muscle cells from parenchymal arterioles from rat brain, using the conventional whole cell patch clamp technique. IKca and SKca channels contribute almost the entire K⁺ current in endothelial cells, and BKca and Kv currents were not observed. Smooth muscle cells have prominent BKca, Kjr and Kv channel currents, without any evidence for IKca and SKca currents. Therefore, endothelial and smooth muscle cells exhibit a differential expression of K⁺ channels.
Selective blockers of SKca and IKca channels (apamin and charybdotoxin) constricted pressurized (40 mmHg) parenchymal arterioles by ~16 % and ~16 %, respectively. In contrast, blocking BKca channels with the selective inhibitor, paxilline. caused only modest (6 %) vasoconstriction. The Kv channel blocker, 4-aminopyridine constricted pressurized parenchymal arterioles by ~25 %. These results indicate that endothelial cell IKca and SKca channels as well as smooth Kv channels have an important role in opposing pressure-induced vasoconstriction. Smooth muscle BKca channels contribute to a lesser extent.
These data support the concept that modulation of K channels in endothelial and smooth muscle cells strongly affects the diameter of parenchymal arterioles. Specifically, activation of either endothelial celllKca channels or smooth muscle Kjr channels causes profound vasodilation, and as such represent potential therapeutic targets to increase blood perfusion in the brain. Conversely, a defect in IKca, SKca, or Kv channel function would lead to vasoconstriction, and thereby compromise cortical cerebral blood flow.