On the Ca2+-permeability of neurons and glia

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Abstract
Fractions enriched in pinched-off [rat] nerve terminals and astrocytic glial cells were used to analyze the permeability of Ca2+ of the 2 membranes. Three experimental models were used to illustrate a principle difference of the excitatory vs. the non-excitatory cell membrane, with respect to Ca permeability. The effect af an increased [Ca2+] on 86Rb+ and 3H-GABA transport was measured in containing low and high [K+]. The possibility of GABA stimulation of release of preaccumulated 45Ca2+ with low and high [K+] was compared in neurons and glia. Finally, the effect of depolarizing [K+] on the transmembranal Ca2+ gradient was measured by comparing the efficacy of the Ca ionophore A23187 to depolarize or to inhibit the 3H-GABA uptake at these different [K+]. The data essentially confirm the picture of a potential dependent Ca2+ permeability in the neuron, while the permeability of the glial cells seems to be a true constant. The astrocyte apparently has a role as a Ca buffer with possibilities to control extracellular Ca2+ in cases of hyperactivity; this in analogy with what has been suggested for K+.

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