Hyperpolarization induces a rise in intracellular sodium concentration in dopamine cells of the substantia nigra pars compacta.
We investigated the effect of changes in membrane-voltage on intracellular sodium concentration ([Na+]i) of dopamine-sensitive neurons of the substantia nigra pars compacta in a slice preparation of rat mesencephalon. Whole-cell patch-clamp techniques were combined with microfluorometric measurements of [Na+]i using the Na+-sensitive probe, sodium-binding benzofuran isophthalate (SBFI). Hyperpolarization of spontaneously active dopamine neurons (recorded in current-clamp mode) caused the cessation of action potential firing accompanied by an elevation in [Na+]i. In dopamine neurons voltage-clamped at a holding potential of -60 mV elevations of [Na+]i were induced by long-lasting (45-60 s) voltage jumps to more negative membrane potentials (-90 to -120 mV) but not by corresponding voltage jumps to -30 mV. These hyperpolarization-induced elevations of [Na+]i were depressed during inhibition of I(h), a hyperpolarization-activated inward current, by Cs+. Hyperpolarization-induced elevations in [Na+]i might occur also in other cell types which express a powerful I(h) and might signal lack of postsynaptic activity.
Knöpfel
T
T
IRCCS S. Lucia, Rome, Italy. knopfel@brain.riken.go.jp
Guatteo
E
E
Bernardi
G
G
Mercuri
N B
NB
D000818:Animals; D004298:Dopamine / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D013378:Substantia Nigra / Q000166:cytology / Q000378:metabolism*
D012964:Sodium; D004298:Dopamine