Neurochemical Research

, Volume 21, Issue 8, pp 889–895 | Cite as

Nigericin-induced Na+/H+ and K+/H+ exchange in synaptosomes: Effect on [3H]GABA release

Original Articles

Abstract

The effect of the putative K+/H+ ionophore, nigericin on the internal Na+ concentration ([Na i ]), the internal pH (pH i ), the internal Ca2+ concentration ([Ca i ]) and the baseline release of the neurotransmitter, GABA was investigated in Na+-binding benzofuran isophtalate acetoxymethyl ester (SBFIAM), 2′,7′-bis(carboxyethyl)-5(6) carboxyfluorescein acetoxymethyl ester (BCECF-AM), fura-2 and [3H]GABA loaded synaptosomes, respectively. In the presence of Na+ at a physiological concentration (147 mM), nigericin (0.5 μM) elevates [Na i ] from 20 to 50 mM, increases thepH i , 0.16 pH units, elevates four fold the [Ca i ] at expense of external Ca2+ and markedly increases (more than five fold) the release of [3H]GABA. In the absence of a Na+ concentration gradient (i.e. when the external Na+ concentration equals the [Na i ]), the same concentration (0.5 μM) of nigericin causes the opposite effect on thepH i (acidifies the synaptosomal interior), does not modify the [Na i ] and is practically unable to elevate the [Ca i ] or to increase [3H]GABA release. Only with higher concentrations of nigericin than 0.5 μM the ionophore is able to elevate the [Ca i ] and to increase the release of [3H]GABA under the conditions in which the net Na+ movements are eliminated. These results clearly show that under physiological conditions (147 mM external Na+) nigericin behaves as a Na+/H+ ionophore, and all its effects are triggered by the entrance of Na+ in exchange for H+ through the ionophore itself. Nigericin behaves as a K+/H+ ionophore in synaptosomes just when the net Na+ movements are eliminated (i.e. under conditions in which the external and the internal Na+ concentrations are equal). In summary care must be taken when using the putative K+/H+ ionophore nigericin as an experimental tool in synaptosomes, as under standard conditions (i.e. in the presence of high external Na+) nigericin behaves as a Na+/H+ ionophore.

Key Words

Nigericin Na+/H+ ionophore K+/H+ ionophore GABA release synaptosomes cytosolic Na+ cytosolic pH cytosolic Ca2+ 

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Copyright information

© Plenum Publishing Corporation 1996

Authors and Affiliations

  1. 1.Depto. de Biología Celular, Instituto de Investigaciones BiomédicasUNAMMéxico

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