Relationships between the neuronal sodium/potassium pump and energy metabolism. Effects of K+, Na+, and adenosine triphosphate in isolated brain synaptosomes.
The relationships between Na/K pump activity and adenosine triphosphate (ATP) production were determined in isolated rat brain synaptosomes. The activity of the enzyme was modulated by altering [K+]e, [Na+]i, and [ATP]i while synaptosomal oxygen uptake and lactate production were measured simultaneously. KCl increased respiration and glycolysis with an apparent Km of about 1 mM which suggests that, at the [K+]e normally present in brain, 3.3-4 mM, the pump is near saturation with this cation. Depolarization with 6-40 mM KCl had negligible effect on ouabain-sensitive O2 uptake indicating that at the voltages involved the activity of the Na/K ATPase is largely independent of membrane potential. Increases in [Na+]i by addition of veratridine markedly enhanced glycoside-inhibitable respiration and lactate production. Calculations of the rates of ATP synthesis necessary to support the operation of the pump showed that greater than 90% of the energy was derived from oxidative phosphorylation. Consistent with this: (a) the ouabain-sensitive Rb/O2 ratio was close to 12 (i.e., Rb/ATP ratio of 2); (b) inhibition of mitochondrial ATP synthesis by Amytal resulted in a decrease in the glycoside-dependent rate of 86Rb uptake. Analyses of the mechanisms responsible for activation of the energy-producing pathways during enhanced Na and K movements indicate that glycolysis is predominantly stimulated by increase in activity of phosphofructokinase mediated via a rise in the concentrations of adenosine monophosphate [AMP] and inorganic phosphate [Pi] and a fall in the concentration of phosphocreatine [PCr]; the main moving force for the elevation in mitochondrial ATP generation is the decline in [ATP]/[ADP] [Pi] (or equivalent) and consequent readjustments in the ratio of the intramitochondrial pyridine nucleotides [( NAD]m/[NADH]m). Direct stimulation of pyruvate dehydrogenase by calcium appears to be of secondary importance. It is concluded that synaptosomal Na/K pump is fueled primarily by oxidative phosphorylation and that a fall in [ATP]/[ADP][Pi] is the chief factor responsible for increased energy production.
Erecińska
M
M
Department of Pharmacology, University of Pennsylvania, Philadelphia 19104.
Dagani
F
F
D000255:Adenosine Triphosphate / Q000096:biosynthesis / Q000502:physiology; D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003847:Deoxyglucose / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology*; D066298:In Vitro Techniques; D007773:Lactates / Q000096:biosynthesis; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D011188:Potassium / Q000502:physiology; D011767:Pyruvate Decarboxylase / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D013574:Synaptosomes / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
D007773:Lactates; D014701:Veratridine; D000255:Adenosine Triphosphate; D003847:Deoxyglucose; D012964:Sodium; D011767:Pyruvate Decarboxylase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D002118:Calcium