title: Differential role of IK and BK potassium channels as mediators of intrinsic and extrinsic apoptotic cell death.
abstract: An important event during apoptosis is regulated cell condensation known as apoptotic volume decrease (AVD). Ion channels have emerged as essential regulators of this process mediating the release of K(+) and Cl(-), which together with osmotically obliged water, results in the condensation of cell volume. Using a Grade IV human glioblastoma cell line, we examined the contribution of calcium-activated K(+) channels (K(Ca) channels) to AVD after the addition of either staurosporine (Stsp) or TNF-α-related apoptosis-inducing ligand (TRAIL) to activate the intrinsic or extrinsic pathway of apoptosis, respectively. We show that AVD can be inhibited in both pathways by high extracellular K(+) or the removal of calcium. However, BAPTA-AM was only able to inhibit Stsp-initiated AVD, whereas TRAIL-induced AVD was unaffected. Specific K(Ca) channel inhibitors revealed that Stsp-induced AVD was dependent on K(+) efflux through intermediate-conductance calcium-activated potassium (IK) channels, while TRAIL-induced AVD was mediated by large-conductance calcium-activated potassium (BK) channels. Fura-2 imaging demonstrated that Stsp induced a rapid and modest rise in calcium that was sustained over the course of AVD, while TRAIL produced no detectable rise in global intracellular calcium. Inhibition of IK channels with clotrimazole or 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) blocked downstream caspase-3 activation after Stsp addition, while paxilline, a specific BK channel inhibitor, had no effect. Treatment with ionomycin also induced an IK-dependent cell volume decrease. Together these results show that calcium is both necessary and sufficient to achieve volume decrease and that the two major pathways of apoptosis use unique calcium signaling to efflux K(+) through different K(Ca) channels.
authors.affiliation: Deptartment of Neurobiology and Center for Glial Biology in Medicine, Universtiy of Alabama at Birmingham, 1719 6th Ave. South, CIRC 410, Birmingham, AL, 35294, USA.
authors.forename: Michael B
authors.initials: MB
authors.lastname: McFerrin
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Turner
authors.forename: Vishnu Anand
authors.initials: VA
authors.lastname: Cuddapah
authors.forename: Harald
authors.initials: H
authors.lastname: Sontheimer
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D003022:Clotrimazole / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000502:physiology; D005910:Glioma / Q000378:metabolism*; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D019311:Staurosporine / Q000494:pharmacology; D053221:TNF-Related Apoptosis-Inducing Ligand
chemical_list: D004791:Enzyme Inhibitors; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D053221:TNF-Related Apoptosis-Inducing Ligand; D003022:Clotrimazole; D019311:Staurosporine; D011188:Potassium; D002118:Calcium