DIFFERENTIAL-EFFECTS OF POTASSIUM CHANNEL BLOCKERS ON EXTRACELLULAR CONCENTRATIONS OF DOPAMINE AND 5-HT IN THE STRIATUM OF CONSCIOUS RATS

1 The selective Ca2+-activated K+ channel blocker apamin increased ext racellular 5-hydroxytryptamine (5-HT) concentrations in the striatum w hen administered through the microdialysis probe at doses of 0.1 mM an d 1 mM. Extracellular dopamine concentrations increased only at the hi ghest dose administered (1 mM). 2 Mast cell degranulating peptide (MCD P), which blocks the dendrotoxin sensitive delayed rectifier (DR) curr ent, increased extracellular concentrations of dopamine at doses of 10 mu M-100 mu M but had no effect on 5-HT. 3 The non selective K+ chann el blocker tetraethylammonium (TEA) induced a dose-dependent (1 mM-10 mM) increase in extracellular dopamine concentrations and an increase in 5-HT which showed little or no dose-dependency. 4 4-Aminopyridine ( 4-AP), a blocker with some similar characteristics to MCDP, increased extracellular dopamine concentrations at doses of 10 mu M-1 mM, but ha d no effect on 5-HT. 5 These findings suggest that dopamine release ma y be modulated by DR-like current and/or A-current K+ channels. Howeve r, in view of the similar effects of MCDP and 4-AP at the concentratio ns used it is more likely that the dendrotoxin-sensitive DR-like curre nt is involved. In contrast, 5-HT release appears to be modulated by C a2+-activated K+ channels.