L-type Ca2+ channels, found in vascular smooth muscle cells, function to control
Ca2+ influx, which directly regulates the degree of tension in the vasculature. An influx
of Ca2+ causes these cells to contract while inhibition of this channel causes muscle
relaxation, a major goal in treating hypertension. Acute hypoxia inhibits, and chronic
hypoxia enhances, Ca2+ channel currents. The mechanisms underlying these hypoxic
responses were examined in HEK 293 cells by altering cellular levels of proposed
mediators of 0 2 sensing which have previously been shown to be involved in the redox
model of 02 sensing in various cell types. In these studies I investigated the roles of
mitochondrial complexes and NADPH oxidase function, and changes in cellular ROS
levels, on the acute and chronically hypoxic regulation of recombinant L-type Ca2+
channels. An increase in H202, a form of ROS, by exogenous application was found to
enhance Ca2+ currents. However neither catalase nor H202 affected the acute hypoxic
response. In contrast superoxide dismutase (SOD) abolished hypoxic inhibition of
recombinant L-type Ca2+ channels, suggestive of a role of 02- production in 02 sensing.
Altered production of this ROS during hypoxia may occur within the mitochondria since
acute 02 sensing was abolished in mitochondria-depleted p0 cells. Alterations in
NADPH oxidase activity via application of NADPH oxidase inhibitors such as DPl and
P AO did not mediate the acute hypoxic response. Hypoxic regulation of mitochondrial
complex I may also mediate the response to chronic hypoxia since current enhancement
by this stimulus was abolished by rotenone. These findings support the involvement of
altered mitochondrial function in the 0 2 sensing pathway which mediates the hypoxic
responses of recombinant L-type Ca2+ channel a1c subunits. / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22669 |
| Date | 07 1900 |
| Creators | Hudasek, Kristin |
| Contributors | Fearon, Ian M., Biology |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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