Ionic dependence of membrane potential and glutamate receptor-linked responses in synaptoneurosomes as measured with a cyanine dye, DiS-C2-(5).

K E Akerman, I G Scott, J E Heikkilä, E Heinonen

Index: J. Neurochem. 48(2) , 552-9, (1987)

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Abstract

Membrane potentials of particles present in a subcellular brain preparation, called synaptoneurosomes, have been monitored by measurement of changes in the absorbance of a cyanine dye, DiS-C2-5. The membrane potential of the particles seems to be dependent on both Cl- and K+ diffusion potentials, as judged from dependence of the absorbance changes on the K+ equilibrium potential across the membrane in the presence of Ba2+ or when Cl- was replaced with gluconate. The apparent high Cl- permeability of the membrane preparation was reduced in the presence of picrotoxin, a finding suggesting endogenous activation of receptor-linked Cl- channels. Glutamate and kainate caused depolarization of the membranes present in the preparation. This effect was only seen if K+ channels had been blocked in the presence of Ba2+ or 4-aminopyridine. No responses were observed with other glutamate receptor agonists (quisqualate or N-methyl-D-aspartate). The membrane potential of particles present in conventional synaptosomal preparations neither had a high Cl- permeability nor reacted to glutamate or kainate in the present conditions. The results suggest that synaptoneurosome preparations may be used for functional studies on postsynaptic neurotransmitter receptor-linked membrane potential changes with optical probes of membrane potential.