3,4-Diaminopyridine-evoked noradrenaline release in rat hippocampus: role of Na+ entry on Ca2+ pools and of protein kinase C.
Slices of rat hippocampus, preincubated with [3H]noradrenaline [(3H]NA), were superfused continuously and stimulated by addition of 3,4-diaminopyridine (3,4-DAP; 100 microM) for 10 min to the superfusion medium. An overflow of 3H evoked by 3,4-DAP (representing [3H]NA release) was measurable not only in the presence but also in the absence of extracellular Ca2+. Both the protein kinase C (PKC) activator 4 beta-phorbol 12,13-dibutyrate (4 beta-PDB) and the PKC inhibitor polymyxin B, affected mainly the evoked release in the absence of extracellular Ca2+ in a facilitatory or inhibitory manner, respectively. Moreover, in the absence of extracellular Ca2+, both the 3,4-DAP-evoked [3H]NA release and the facilitatory effect of 4 beta-PDB were abolished in the presence of tetrodotoxin or in the absence of Na+ in the superfusion medium. Ruthenium red, a blocker of mitochondrial Ca2+ reuptake, potently increased 3,4-DAP-evoked [3H]NA release in Ca(2+)-free EGTA-containing medium. The facilitatory effects of ruthenium red and 4 beta-PDB were additive. From these and earlier observations we conclude (1) that the mechanism of 3,4-DAP-evoked [3H]NA release involves both Ca2+ influx into the nerve terminals and mobilization of intraneuronal Ca2+ pools. Most probably Ca2+ release from cytoplasmic Ca2+ stores (e.g. endoplasmic reticular pools or mitochondria) is induced by Na+ ions entering the nerve endings during 3,4-DAP-evoked repetitive action potentials. (2) The facilitatory effect of phorbol ester on 3,4-DAP-evoked NA release appears to be mediated not by changes in Ca2+ influx, but by enhancement of intraneuronal events distal to Na+ ion entry and increased intracellular Ca2+ availability.
Huang
H Y
HY
Shanghai Institute of Physiology, Chinese Academy of Sciences.
Hertting
G
G
Allgaier
C
C
Jackisch
R
R
D015761:4-Aminopyridine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000077770:Amifampridine; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D018377:Neurotransmitter Agents / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011112:Polymyxin B / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012430:Ruthenium Red / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D018377:Neurotransmitter Agents; D012430:Ruthenium Red; D015240:Phorbol 12,13-Dibutyrate; D013779:Tetrodotoxin; D012964:Sodium; D015761:4-Aminopyridine; D011493:Protein Kinase C; D011112:Polymyxin B; D000077770:Amifampridine; D002118:Calcium; D009638:Norepinephrine