The most common and most malignant gliomas are the Grade IV Glioblastoma Multiforme (GBM), characterized by a highly proliferative tumor mass and extremely invasive phenotype that allows for profuse dispersal of tumor cells throughout the brain. GBM cells must specifically regulate their cell volume to thrive within the edematous tumor mass and infiltrate throughout the tortuous extracellular spaces of the brain. These rapid and directed volume changes are governed by the controlled flux of potassium and chloride ions across the cell membrane, which move osmotically obliged water. The goal of this dissertation was to investigate the role of calcium-activated potassium channels (KCa channels) in regulating the potassium efflux pathways during volume change. The KCa channels are the major contributors to potassium conductance in GBM cells and are ideal for translating calcium changes into potassium efflux and volume decrease. In this dissertation, I report the activity of the IK channel, previously unknown to be expressed in GBM cells, in addition to the well characterized BK channel. Both K Ca channels are biochemically isolated in lipid-raft domains together with the ClC-3 chloride channel and co-localize in lipid-raft domains in situ, suggesting that these channels are coordinated to specific areas of the plasma membrane for directed movement of KCl. During apoptosis cells undergo apoptotic volume decrease (AVD) that requires volume decrease under normotonic conditions. I demonstrate that the intrinsic pathway, induced by staurosporine, initiates AVD through IK channels in a manner that is dependent on global calcium increase. Blockade of IK channels with clotrimazole or TRAM-34 significantly reduced AVD and impaired downstream caspase-3 activation. In contrast, the extrinsic pathway, stimulated by treatment with TRAIL, induced a paxilline sensitive AVD and caused no detectable changes in calcium. Finally, during exposure to hypotonic solution, GBM cells swell and regulate their volume back to baseline using potassium efflux primarily through IK channels. This regulatory volume decrease (RVD) was blocked by clotriamazole and TRAM-34 while paxillne was ineffective at preventing RVD. These studies have revealed IK channels as an intriguing new player in GBM biology, especially in volume regulation and possibly many other processes integral for GBM malignancy.
|Commitee:||Hablitz, John, Nabors, L. Burt, Olsen, Michelle, Theibert, Anne|
|School:||The University of Alabama at Birmingham|
|School Location:||United States -- Alabama|
|Source:||DAI-B 73/04, Dissertation Abstracts International|
|Subjects:||Neurosciences, Cellular biology|
|Keywords:||Apoptosis, Bk channel, Calcium-activated potassium channels, Glioma, Ik channel, Volume regulation|
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