Cobalt-sensitive and dihydropyridine-insensitive stimulation of dopamine release from tuberoinfundibular neurons by high extracellular concentrations of barium ions.
Recently, it has been demonstrated that Ca2+ entrance into the neuronal cytoplasm can occur upon the activation of 3 different types of specific voltage-dependent channels which can be characterized according to the following criteria: (1) voltage threshold for activation; (2) tendency to inactivation; (3) bivalent cation permeability; and (4) drug sensitivity. In this study we investigated, in tuberoinfundibular dopaminergic (TIDA) hypothalamic neurons, the biochemical and pharmacological properties of Ca2+ channels, by comparing the effects of high extracellular concentrations of Ba2+ and Ca2+ ions on [3H]dopamine (DA) release from TIDA neurons. The results obtained show that extracellular Ba2+ ion concentrations dose-dependently (10-20 mM) stimulated [3H]DA release from superfused TIDA neurons and that this effect was prevented by Co2+ ions (2 mM). In addition, superfusion of TIDA neurons with a concentration of Ca2+ ions equimolar to that of Ba2+ ions (20 mM) failed to modify [3H]DA release. The fact that tetraethylammonium (10 mM), a blocker of K+ currents in excitable cells, did not mimick the stimulatory action of Ba2+ ions on [3H]DA release, seems to exclude that the effect of Ba2+ ions was dependent on the inhibition of K+ channels in TIDA neurons. The omission of Ca2+ ions from the extracellular medium did not prevent the stimulatory effect on [3H]DA release elicited by elevated concentrations of Ba2+ ions, but rather reinforced this effect. Finally, nitrendipine (50 microM) did not modify the stimulatory effect of high extracellular Ba2+ ions on [3H]DA release from TIDA neurons.
Taglialatela
M
M
Institute of Pharmacology, 2nd School of Medicine, University of Naples, Italy.
Canzoniero
L M
LM
Amoroso
S
S
Fatatis
A
A
Di Renzo
G F
GF
Annunziato
L
L
D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology*; D004095:Dihydropyridines / Q000494:pharmacology*; D004298:Dopamine / Q000493:pharmacokinetics*; D005260:Female; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D009568:Nitrendipine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D002413:Cations, Divalent; D004095:Dihydropyridines; D001464:Barium; D003035:Cobalt; C038806:1,4-dihydropyridine; D009568:Nitrendipine; D004298:Dopamine