Involvement of phospholipase A2 and arachidonic acid in the depolarization-evoked accumulation of Ca2+ in hippocampal mossy fiber nerve endings.
Depolarization-evoked increases in intraterminal free Ca2+ are required for the induction of neurotransmitter release from nerve terminals. Although the mechanisms that regulate the voltage-induced accumulation of presynaptic Ca2+ remain obscure, there is evidence that the phospholipase-dependent accumulation of arachidonic acid, or its metabolites, may be involved. Therefore, fura-2 loaded hippocampal mossy fiber nerve endings were used to investigate the relationships between membrane depolarization, lipid metabolism and presynaptic Ca2+ availability. It was observed that depolarization of the nerve terminals with KCl induced an increase in intraterminal free calcium that was inhibited more than 90% by a combination of voltage-sensitive Ca2+ channel blockers. In addition, the K(+)-dependent effects on Ca2+ concentrations were attenuated in the presence of phospholipase A2 inhibitors, but were mimicked by the phospholipase A2 activator melittin and exogenous arachidonic acid. Both the melittin- and arachidonic acid-induced increases in presynaptic Ca2+ were reduced by voltage-sensitive Ca2+ channel blockers. The stimulatory effects of arachidonic acid appeared to be independent of its further metabolism to prostaglandins. In fact, inhibition of either cyclooxygenase or lipoxygenase pathways resulted in a potentiation of the depolarization-evoked increase in intraterminal free Ca2+. From these results, we propose that some portion of the depolarization-evoked increase in intraterminal free calcium depends on the activation of phospholipase A2 and the subsequent accumulation of unesterified arachidonic acid.
Damron
D S
DS
Department of Biological Sciences, Kent State University, Ohio 44242.
Dorman
R V
RV
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D005227:Fatty Acids / Q000494:pharmacology; D044950:Flavanones; D005419:Flavonoids / Q000494:pharmacology; D006624:Hippocampus / Q000378:metabolism*; D007052:Ibuprofen / Q000494:pharmacology; D008049:Lipase / Q000037:antagonists & inhibitors; D008555:Melitten / Q000494:pharmacology; D009411:Nerve Endings / Q000378:metabolism*; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D011189:Potassium Chloride / Q000494:pharmacology; D011453:Prostaglandins / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology
D005227:Fatty Acids; D044950:Flavanones; D005419:Flavonoids; D011453:Prostaglandins; D008555:Melitten; D016718:Arachidonic Acid; D013779:Tetrodotoxin; C006680:baicalein; D011189:Potassium Chloride; D008049:Lipase; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium; D007052:Ibuprofen