Effects of hypoxia, anoxia, and metabolic inhibitors on K_ATP channels in rat femoral artery myocytes

Abstract

Effects of hypoxia, anoxia, and metabolic inhibitors on KATP channels in rat femoral artery myocytes. Am J Physiol Heart Circ Physiol 291: H71-H80, 2006. First published February 17, 2006 doi:10.1152/ajpheart.01107.2005.-Vascular ATP-sensitive potassium (KATP) channels have an important role in hypoxic vasodilation. Because KATP channel activity depends on intracellular nucleotide concentration, one hypothesis is that hypoxia activates channels by reducing cellular ATP production. However, this has not been rigorously tested. In this study we measured K ATP current in response to hypoxia and modulators of cellular metabolism in single smooth muscle cells from the rat femoral artery by using the whole cell patch-clamp technique. KATP current was not activated by exposure of cells to hypoxic solutions (PO2 ϳ35 mmHg). In contrast, voltagedependent calcium current and the depolarization-induced rise in intracellular calcium concentration ([Ca 2ϩ ]i) was inhibited by hypoxia. Blocking mitochondrial ATP production by using the ATP synthase inhibitor oligomycin B (3 M) did not activate current. Blocking glycolytic ATP production by using 2-deoxy-D-glucose (5 mM) also did not activate current. The protonophore carbonyl cyanide m-chlorophenylhydrazone (1 M) depolarized the mitochondrial membrane potential and activated K ATP current. This activation was reversed by oligomycin B, suggesting it occurred as a consequence of mitochondrial ATP consumption by ATP synthase working in reverse mode. Finally, anoxia induced by dithionite (0.5 mM) also depolarized the mitochondrial membrane potential and activated K ATP current. Our data show that: 1) anoxia but not hypoxia activates KATP current in femoral artery myocytes; and 2) inhibition of cellular energy production is insufficient to activate K ATP current and that energy consumption is required for current activation. These results suggest that vascular K ATP channels are not activated during hypoxia via changes in cell metabolism. Furthermore, part of the relaxant effect of hypoxia on rat femoral artery may be mediated by changes in [Ca 2ϩ ]i through modulation of calcium channel activity. smooth muscle; ion channels; potassium channels ATP-SENSITIVE POTASSIUM (K ATP ) channels are involved in the hypoxic vasodilation that couples blood flow to metabolic demand, for example, in the coronary (44), skeletal muscle (30), and cerebral circulations (42). Hypoxia is thought to activate K ATP channels either by acting directly on the smooth muscle cells or by causing release of vasodilator metabolites from surrounding tissue or endothelial cells, which in turn activates channels via receptor-coupled signal transduction pathways (e.g., 9, 23, 30, 37, 43, 44). K ATP channels are regulated by intracellular ATP and ADP, and the direct vasodilator action of hypoxia may therefore occur as a consequence of hypoxia changing intracellular nucleotide levels in arterial myocytes (9, 27, 44). Alternatively, oxygen tension regulates the activity of some channels independently of changes i...

Hypoxia. 4. Hypoxia and ion channel function

“…In some studies, hypoxia activated glibenclamide-sensitive K ϩ currents in amphotericin B-perforated cells of isolated porcine coronary SMCs (44) and hypoxia-induced relaxation was at least partially inhibited by K ATP blockers in thoracic aorta (91) and cremaster (108), carotid (215), and cerebral (64) arteries. However, in other studies, hypoxia did not increase K ATP current of voltage-clamped, amphotericin B-perforated cells (108,182) and hypoxic relaxations were resistant to glibenclamide (204). Whether these variations in findings are due to species and/or vascular bed differences is unclear.…”

Hypoxia-induced Acidosis Uncouples the STIM-Orai Calcium Signaling Complex

“…(a) Control solutions (either for imaging or electrophysiology) were mixed with freshly prepared sodium dithionite (Na 2 S 2 O 4 ) solution to give a final 1 mM concentration sufficient to reduce pO 2 to low levels (21,22); pH was adjusted to 7.4, and the solution was bubbled with 100% N 2 . (b) Normal media were bubbled for Ͼ30 min with 100% N 2 .…”

Hypoxia sensing in the fetal chicken femoral artery is mediated by the mitochondrial electron transport chain

“…The mediator, in turn, alters the function of one or more effectors, which ultimately mediate the physiological response of the system (3, 58). Numerous experimental evidences point to the mitochondrial electron transport chain (mETC) as the sensor, reactive O 2 species (ROS) as mediators, and K ϩ channels as effectors of the vascular response to acute hypoxia (3,10,26,35,44,52,53,55,56,58,59), and it has been suggested that differences between pulmonary and systemic arteries in this sensing/signaling system may account for the opposite responses of these vessels to the hypoxic stimulus (52).The present information about the response to hypoxia in blood vessels from nonmammalian species suggests largely similar mechanisms as in mammals (32,42,43). In the last few years, the chicken embryo/fetus has emerged as a suitable model for the study of numerous aspects of developmental vascular biology, including the response to acute and chronic changes in oxygenation (1,9,38,39,47,50,51,63).…”