Intracellular ion activities and equilibrium potentials in motoneurones and glia cells of the frog spinal cord

Abstract

Intra- and extracellular ion activities were measured with ion sensitive microelectrodes in motoneurones and glia cells of the spinal cord of the frog. These data were corrected for cross sensitivities of the ion exchangers to intracellular interfering ions, and equilibrium potentials for K⁺, Na⁺, Ca²⁺ and Cl⁻ (E _K,E _Na,E _Ca andE _Cl) were calculated. In motoneurones with membrane potentials exceeding −60mV the following mean equilibrium potentials were determined.

$$\begin{gathered} E_{Na} = + 29.4mV, E_K = - 87.9mV, E_{Ca} = + 52.6mV, \hfill \\ E_{Cl} = - 34.1mV \hfill \\ \end{gathered}$$

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The corresponding values for glia cells were:

$$\begin{gathered} E_{Na} = + 40.5mV, E_K = - 84.0mV, E_{Ca} = + 35.7mV, \hfill \\ E_{Cl} = - 59.7mV \hfill \\\end{gathered}$$

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The intracellular ionic milieu is probably disturbed by the impalement of the cells. This transiently decreases the intracellular K⁺ and increases intracellular Na⁺. These effects were estimated and their origin is discussed. The results of the experiments suggest a non-passive transmembrane distribution of K⁺, Na⁺ and Ca²⁺ in motoneurones and glia cells, a non-passive transmembrane distribution of Cl⁻ in motoneurones, and a passive transmembrane distribution of Cl⁻ in glia cells.