[The consequences of sodium pump inhibition in the neurons and its relevance to the physiopathology of the cell damage produced by anoxic ischemia].
The effect of altering the transmembrane electrochemical Na+ gradient on total membrane conductance (Gm) of Helix aspersa neurones was investigated with intracellular microelectrode recording techniques. Replacement of extracellular Na+ with an impermeant cation (glucamine) produced a modest and short lived decrease in Gm (4.6 +/- 2.9%) followed by a prominent and sustained increase of it (30.3 +/- 10.5%). The latter effect was accompanied by membrane hyperpolarization. These results suggest that removal of external Na+ leads to an increase in [Ca++]i probably through the Na+/Ca++ exchanger operating in reverse mode. The resulting rise in [Ca++]i would be sufficient to produce an increase in membrane permeability to K+. Inhibition of the Na+ pump with ouabain results in a similar increase in Gm, suggesting a rise in [Ca++]i through the Na+/Ca++ exchanger and voltage-sensitive Ca++ channels. Mathematical modelling of Na+/Ca++ exchange in these neurones showed that modest increments in [Na+]i produce significant increases in [Ca++]i in agreement with [Na+]i and [Ca++] measurements performed with fluorescent indicators and ion-selective microelectrode techniques. The results are discussed in relation with the cellular changes occurring in ischemic-anoxic nervous tissue.
Alvarez Leefmans
F J
FJ
Departamento de Neurobiología, Instituto Mexicano de Psiquitría.
Merediz Alonso
G
G
Fernández Calderón
J R
JR
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology; D003864:Depression, Chemical; D004553:Electric Conductivity; D006372:Helix, Snails; D066298:In Vitro Techniques; D008536:Meglumine / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008839:Microelectrodes; D008959:Models, Neurological; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects* / Q000502:physiology
D010042:Ouabain; D008536:Meglumine; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium