Prostaglandin release but not superoxide production by rat Kupffer cells stimulated in vitro depends on Na⁺/H⁺ exchange

Abstract

The release of the prostaglandins E2 and D2, induced by zymosan and phorbol ester in cultured rat Kupffer cells, was found to depend on the extracellular concentration of Na'. Eicosanoid formation following the administration of the Ca2+ ionophore A23187 or of arachidonic acid, however, did not require the presence of sodium ions in the medium. A half-maximal rate of prostaglandin release by zymosan-treated Kupffer cells was obtained between 4 mM and 5 mM Na'; and a Na' concentration of 2 30 mM was required to maximally stimulate prostaglandin E2 and D, formation in the cultured liver macrophages. In contrast, the superoxide production following the administration of zymosan or of phorbol ester was quite independent of extracellular Na'.The zymosan and phorbol-ester-stimulated release of prostaglandins E, and D2 was inhibited by amiloride. Artificial intracellular alkalization enhanced the prostanoid production of unstimulated and of zymosan-stimulated cells whereas artificial intracellular acidification inhibited the zymosan-elicited prostaglandin synthesis. In contrast, the superoxide formation was independent of the pH changes. The data presented here suggest that the prostaglandin production elicited by zymosan or phorbol ester in cultured rat Kupffer cells requires an activated Na'/Hf exchange.

Inhibition of Lipopolysaccharide-Induced Prostaglandin E2Production and Inflammation by the Na+/H+Exchanger Inhibitors

“…1). Our findings that the NHE inhibitors reduced the LPS-induced production of PGE 2 did not conflict with the observation that amiloride inhibits phorbol ester-and zymosan-induced PGE 2 production in Kupffer cells (Dieter et al, 1987). Amiloride (100 M) inhibited PGE 2 production more potently than 10 M DMA and 3 M EIPA, although the inhibitory effect on NHE among these drugs at the concentrations used was nearly the same (Masereel et al, 2003).…”

Biologically active products of stimulated liver macrophages (Kupffer cells)

“…The very low intracellular basal level of the free ion (< 0.2 pM) can be changed by the InsP3-stimulated influx from the storage sites (mainly endoplasmatic reticulum, but to some extent also mitochondria), the net uptake from the outside by activation of Ca2+ channels, antiporters (2 Na'/ Ca"), or by modulation of the activity of the ATP-driven Ca2+ pump. The intracellular Ca2+ level is also related to the internal pH; activation of the N a + / H + antiporter [72] and eicosanoid synthesis [73], e.g. after zymosan addition, in rat Kupffer cells is connected with a transcellular Ca2 + influx [70] (Fig.…”

Ca2+ requirement of prostanoid but not of superoxide production by rat Kupffer cells

“…The significance of the percentage differences between inhibited and uninhibited synthesis was calculated using Student's t test analysis of +TMB 8 vs -TMB 8 experiments; ns., not significant Table 3. showing that the generation of prostanoids and superoxide are differently regulated in Kupffer cells: the formation of prostanoids but not of superoxide was shown to depend on extracellular Na+ [4] and was inhibited by dexamethasone treatment of the cells [3]. In other cell types the role of Ca2+ in the activation of superoxide formation is still controversial.…”

“…It has been shown recently that the stimulusinduced release of prostanoids but not of superoxide depends on the extracellular concentration of Na' and that an N a + / H + exchange and a concomitant change in the cellular pH value are involved in the stimulus response coupling [4]. However, the exact sequence of events during the activation process is not known.…”

“…The Ca2+/EGTA buffer system was calculated according to Fabiato [15,16]. For manipulation of the intracellular pH the cells were incubated in Hanks solution (122 mM KCl, 5.4 mM NaCl, pH 8.4) containing the K f / H + ionophore nigericin (1 pM) [4]. All inhibitors were added 15 min prior to the addition of the stimuli.…”