Arachidonic acid stimulates the plasma membrane H+ conductance of macrophages.
When activated, phagocytes undergo a large burst of metabolic acid production. Deleterious cytosolic acidification is prevented by extrusion of H+ (equivalents) through specific transport systems, including a recently described H+ conductive pathway. The conductance can be activated by cytosolic acidification and by depolarization, events known to occur during phagocyte activation. It is possible, however, that the conductance is also directly stimulated by agonists or second messengers. In this report, spectroscopic and electrophysiological determinations were used to assess the effects of arachidonic acid (AA), a potent phagocyte stimulant, on the plasmalemmal H+ conductance of murine macrophages. AA greatly enhanced the slowly activating H+ currents and the cytosolic alkalinization triggered by depolarizing pulses. The H+ current in AA-treated cells appeared at more negative potentials and its activation and deactivation became faster. The ionic selectivity, outward rectification, and pharmacological properties of the stimulated current were identical to those of the basal current, suggesting that AA acts by facilitating the activation of the endogenous H+ conductive pathway, rather than by exerting a protonophoric effect. Experiments using specific inhibitors suggested that the effects of AA are not mediated by lipo- or cyclooxygenase. Comparison of the effects of a variety of fatty acids supported this conclusion. The order of potency to stimulate the conductance was: AA > palmitoleate approximately palmitelaidate > linoleate > oleate > elaidate. Saturated fatty acids were inactive. This sequence shows striking similarity with the ability of these lipids to stimulate the NADPH oxidase. The results indicate that, simultaneously with the activation of metabolic acid generation, phagocyte agonists also directly activate regulatory H+ extrusion, thereby favoring maintenance of intracellular pH in the physiological range.
Kapus
A
A
Division of Cell Biology, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
Romanek
R
R
Grinstein
S
S
D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D002448:Cell Adhesion; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology; D006859:Hydrogen / Q000378:metabolism*; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000502:physiology*; D015636:Magnesium Chloride / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D013329:Structure-Activity Relationship
D005230:Fatty Acids, Nonesterified; D007473:Ion Channels; D015636:Magnesium Chloride; D016718:Arachidonic Acid; D004533:Egtazic Acid; D006859:Hydrogen