valinomycin and Hypoxia

System y+ accounts for the majority of L-arginine transport by pulmonary artery endothelial cells (PAEC). Given that membrane potential is a driving force for transport via system y+, we examined the hypothesis that hypoxia inhibits this transport by decreasing membrane potential. Porcine PAEC or plasma membrane vesicles derived from these cells were exposed to normoxia (room air-5% CO2) or hypoxia (0% O2-95% N2-5% CO2). After exposure, L-[3H]arginine transport and/or accumulation of the lipophilic cation [3H]tetraphenylphosphonium, a quantitative sensor of changes in cell membrane potential, were measured. Hypoxia caused reversible time-dependent decrease in L-arginine transport and membrane potential in PAEC and in plasma membrane vesicles. Comparable decreases in membrane potential and L-arginine transport by PAEC were also observed after depolarization induced by KCl or ouabain. Hyperpolarization, induced by valinomycin, increased membrane potential and L-arginine transport in PAEC and plasma membrane vesicles. Valinomycin also prevented the hypoxia-mediated decreases in membrane potential and L-arginine transport in PAEC. These results indicate that hypoxia-induced plasma membrane depolarization is responsible for reduced L-arginine transport by system y+ in hypoxic porcine PAEC.

Topics: Animals; Arginine; Biological Transport; Cell Membrane; Endothelium, Vascular; Hypoxia; Membrane Potentials; Onium Compounds; Organophosphorus Compounds; Ouabain; Potassium; Pulmonary Circulation; Sodium; Swine; Valinomycin

The precise mechanism by which altered oxidative metabolism impairs neuronal function is unknown. Previous indirect studies suggest that anoxia's effects on the mitochondrial membrane potentials may underlie anoxia's actions. Twenty minutes of anoxia reduced the mitochondrial membrane potential of intact synaptosomes by 38-59 mV, but diminished the plasma membrane potential by only 4-10 mV. Anoxia did not alter the response of the plasma or mitochondrial membrane potentials to K+, nor did anoxia affect the reaction of the plasma membrane potential to valinomycin. However, anoxia diminished the response of the mitochondrial membrane potential to valinomycin by 50%. Thus, partial collapse of the mitochondrial membrane potential may be an important mediator of hypoxia-or anoxia-induced changes in neuronal function.

Topics: Anaerobiosis; Animals; Brain; Cell Membrane; Hypoxia; Intracellular Membranes; Kinetics; Membrane Potentials; Mitochondria; Potassium; Rats; Synaptosomes; Valinomycin