Groups IV, V, and X phospholipases A2s in human neutrophils: role in eicosanoid production and gram-negative bacterial phospholipid hydrolysis.

The bacterial tripeptide formyl-Met-Leu-Phe (fMLP) induces the secretion of enzyme(s) with phospholipase A(2) (PLA(2)) activity from human neutrophils. We show that circulating human neutrophils express groups V and X sPLA(2) (GV and GX sPLA(2)) mRNA and contain GV and GX sPLA(2) proteins, whereas GIB, GIIA, GIID, GIIE, GIIF, GIII, and GXII sPLA(2)s are undetectable. GV sPLA(2) is a component of both azurophilic and specific granules, whereas GX sPLA(2) is confined to azurophilic granules. Exposure to fMLP or opsonized zymosan results in the release of GV but not GX sPLA(2) and most, if not all, of the PLA(2) activity in the extracellular fluid of fMLP-stimulated neutrophils is due to GV sPLA(2). GV sPLA(2) does not contribute to fMLP-stimulated leukotriene B(4) production but may support the anti-bacterial properties of the neutrophil, because 10-100 ng per ml concentrations of this enzyme lead to Gram-negative bacterial membrane phospholipid hydrolysis in the presence of human serum. By use of a recently described and specific inhibitor of cytosolic PLA(2)-alpha (group IV PLA(2)alpha), we show that this enzyme produces virtually all of the arachidonic acid used for the biosynthesis of leukotriene B(4) in fMLP- and opsonized zymosan-stimulated neutrophils, the major eicosanoid produced by these pro-inflammatory cells.

Age-related impairment in long-term potentiation in hippocampus: a role for the cytokine, interleukin-1 beta?

Ageing is associated with impairments in a variety of biological functions, one of the most striking might be considered to be the impairment in cognitive function. This impairment probably relates to the vulnerability of the hippocampus to the ageing process, since several cognitive functions rely on the integrity of this brain area. Analysis of the mechanisms underlying the effect of ageing on hippocampal function has focused to a great extent on analysis of age-related changes in long-term potentiation (LTP) in hippocampus of experimental animals. LTP is a remarkable form of synaptic plasticity which is characterized by a persistent increase in synaptic efficacy following tetanic stimulation of an afferent pathway to one of the hippocampal subfields. On the basis of its properties, LTP has been proposed as a biological substrate for learning and/or memory. There is general agreement that aged rats exhibit an impaired ability to sustain LTP but there is no agreement on the underlying cause of this deficit. In this review, the evidence which suggests that age-related changes in membrane composition, triggered by oxidative changes, might significantly contribute to the impairment in LTP, is considered. These findings are supported by recent data which indicates that dietary supplementation with the antioxidant vitamins, E and C, reversed the age-related impairment in LTP, in parallel with reversing the age-related decrease in alpha-tocopherol concentration and the age-related increase in lipid peroxidation. The possibility that the proinflammatory cytokine, interleukin-1 beta, triggers several age-related changes in hippocampus is considered and, based on the evidence presented, the hypothesis that interleukin-1 beta plays a significant role in ageing in the hippocampus is proposed.

Involvement of extracellular calcium and arachidonate in [3H] dopamine release from rat tuberoinfundibular neurons.

The mechanism of [3H]dopamine [( 3H]DA) release was investigated using primary cultures of dispersed cells from the rat tuberoinfundibular region, which contains tyrosine hydroxylase (TH)-like immunoreactive neurons. The calcium ionophore A23187 at 10 nM and above caused a significant and dose-dependent increase in [3H]DA release. In the presence of 50 microM A23187, [3H]DA release was detectable within 30 s and reached a plateau in 15 min. The induction of [3H]DA release by 50 microM A23187 was abolished by lowering the extracellular calcium concentration with 2 mM EDTA. Maitotoxin, another calcium-channel activator, also increased [3H]DA release at a concentration of 50 ng/ml. Exogenous additions of 100 mIU/ml phospholipase A2 and 10 microM arachidonate caused significant release of [3H]DA. Furthermore, A23187 stimulated [3H]arachidonate release from tuberoinfundibular dopaminergic (TIDA) neurons in a dose- and time-dependent manner. These results suggest that extracellular calcium and arachidonate are involved in the process of [3H]DA release from rat TIDA neurons.