Inhibitory action of fatty acids on calcium fluxes in thyroid FRTL-5 cells

Effect of oleic acid on store-operated calcium entry in immune-competent cells

PURPOSE

To study the mechanism by which oleic acid (OA) (C18:1) exerts its beneficial effects on immune-competent cells. Since store-operated Ca²⁺ entry (SOCE) is a Ca²⁺ influx pathway involved in the control of multiple physiological processes including cell proliferation, we studied the effect of OA in Ca²⁺ signals of Jurkat T cells and THP-1 monocytes, paying particular attention to SOCE.

METHODS

Changes in [Ca²⁺]_i were measured using the Fura-2 fluorescence dye. Mn²⁺ uptake was monitored as a rate of quenching of Fura-2 fluorescence measured at the Ca²⁺-insensitive wavelengths. Thapsigargin was used to induce SOCE in Fura-2-loaded cells.

RESULTS

We showed a clear dose-dependent SOCE-inhibitory effect of OA in both cell lines. Such an inhibitory effect was PKC independent and totally restored by albumin, suggesting that OA exerts its effect somewhere in the membrane. We also demonstrated that OA induces increases in [Ca²⁺]_i partly mediated by an extracellular Ca²⁺ influx through econazole-insensitive channels. Finally, we compared the effect of OA with stearic acid (C18:0), assuming the emerged evidence concerning the link between saturated fats and inflammation disorders. Stearic acid failed to inhibit SOCE, independently on the concentration tested, thus intensifying the physiological relevance of our findings.

CONCLUSION

We suggest a physiological pathway for the beneficial effects of OA in inflammation.

The durative use of suspension cells and callus for volatile oil by comparative with seeds and fruits in Capparis spinosa L

Capparis spinosa is one of the most important eremophytes among the medicinal plants, and continued destruction of these plants poses a major threat to species survival. The development of methods to extract compounds, especially those of medicinal value, without harvesting the whole plant is an issue of considerable socioeconomic importance. On the basis of an established system for culture of suspension cells and callus in vitro, Gas Chromatograph-Mass Spectrometer (GC-MS) was used for the volatile oil composition analyzing in seed, fruit, suspension cells and callus. Fatty acids were the major component, and the highest content of alkanes was detected in seed, with <1.0% in suspension cells and callus. Esters, olefins and heterocyclic compounds were significantly higher in fruit than in the other materials. The content of acid esters in the suspension cells and callus was significantly higher than in seed and fruit. This indicated that the suspension cells and callus could be helpful for increasing the value of volatile oil and replacing seeds and fruit partially as a source of some compounds of the volatile oil and may also produce some new medical compounds. The above results give valuable information for sustainable use of C. spinosa and provide a foundation for use of the C. spinosa suspension cells and callus as an ongoing medical resource.

Dietary virgin olive oil enhances secretagogue-evoked calcium signaling in rat pancreatic acinar cells

OBJECTIVE

We evaluated the long-term effects of a fat-enriched diet (virgin olive oil) on calcium mobilization and amylase secretion induced by cholecystokinin-octapeptide (CCK-8) in rat pancreatic acinar cells. Olive oil is a major component of the Mediterranean diet, and its role in human health is actively being debated.

METHODS

Weaning male Wistar rats (21 d old) were assigned to one of two experimental groups and fed for 8 wk with a commercial chow (control group) or an experimental diet (olive group) containing 100 g/kg of virgin olive oil as dietary fat. Intracellular free calcium [Ca(2+)](i) levels were determined by loading the pancreatic cells with the fluorescent ratio-metric calcium indicator Fura-2 on an inverted fluorescent microscope. For measurement of amylase secretion, cells were incubated with the appropriate secretagogue for 30 min, and amylase activities in the supernatant were determined by the Phadebas blue starch method. Analysis of variance was used to test differences between groups.

RESULTS

Compared with the control group, the CCK-8-induced increase in [Ca(2+)](i) occurred in cells from rats in the olive group (P < 0.05). This stimulatory effect of dietary virgin olive oil was observed in calcium oscillations and large [Ca(2+)](i) transients induced by low (20 pM/L) and high (10 nM/L) concentrations of CCK-8, respectively. In addition to the effects of dietary virgin olive oil on calcium mobilization, it increased (P < 0.05) amylase secretion in response to CCK-8. Olive oil treatment did not significantly alter resting [Ca(2+)](i) or amylase release values compared with the control group. Similar results were obtained when pancreatic acinar cells were stimulated with a high concentration of acetylcholine (10 microM/L).

CONCLUSION

The present results demonstrate that a diet supplemented with virgin olive oil can modify pancreatic cell function as assessed by [Ca(2+)](i) mobilization and amylase release evoked by secretagogues in rat pancreatic acinar cells. A role for fatty acids in calcium signaling is suggested.

Arachidonic acid in astrocytes blocks Ca(2+) oscillations by inhibiting store-operated Ca(2+) entry, and causes delayed Ca(2+) influx

ATP-elicited oscillations of the concentration of free intracellular Ca(2+) ([Ca(2+)](i)) in rat brain astrocytes were abolished by simultaneous arachidonic acid (AA) addition, whereas the tetraenoic analogue 5,8,11,14-eicosatetraynoic acid (ETYA) was ineffective. Inhibition of oscillations is due to suppression by AA of intracellular Ca(2+) store refilling. Short-term application of AA, but not ETYA, blocked Ca(2+) influx, which was evoked by depletion of stores with cyclopiazonic acid (CPA) or thapsigargin (Tg). Addition of AA after ATP blocked ongoing [Ca(2+)](i) oscillations. Prolonged AA application without or with agonist could evoke a delayed [Ca(2+)](i) increase. This AA-induced [Ca(2+)](i) rise developed slowly, reached a plateau after 5 min, could be reversed by addition of bovine serum albumin (BSA), that scavenges AA, and was blocked by 1 microM Gd(3+), indicative for the influx of extracellular Ca(2+). Specificity for AA as active agent was demonstrated by ineffectiveness of C16:0, C18:0, C20:0, C18:2, and ETYA. Moreover, the action of AA was not affected by inhibitors of oxidative metabolism of AA (ibuprofen, MK886, SKF525A). Thus, AA exerted a dual effect on astrocytic [Ca(2+)](i), firstly, a rapid reduction of capacitative Ca(2+) entry thereby suppressing [Ca(2+)](i) oscillations, and secondly inducing a delayed activation of Ca(2+) entry, also sensitive to low Gd(3+) concentration.

Arachidonic acid inhibits capacitative calcium entry in rat thymocytes and human neutrophils

Emptying the intracellular Ca2+ stores by treatment with the endomembrane Ca2+-ATPase inhibitor thapsigargin activates capacitative Ca2+ entry (CCE). This can be evidenced in fura-2-loaded cells by an increase of [Ca2+]i or by an acceleration of Mn2+ entry. Micromolar concentrations of arachidonic acid inhibited CCE induced by treatment with thapsigargin in rat thymocytes and in human neutrophils. This inhibitory action was shared by other unsaturated fatty acids, but not by the saturated arachidic acid nor by arachidonic acid methyl ester. The effect was not due to metabolites derived from arachidonic acid since several non-metabolizable analogs were able to reproduce it. Phorbol dibutyrate (PDB) acted similarly, suggesting that the inhibitory effect could be mediated by activation of protein kinase C (PKC). However, whereas the inhibition of CCE by PDB was reversed by treatment with the PKC inhibitor staurosporin, the inhibition by arachidonic acid was not. We find that unsaturated fatty acids antagonized microsomal dealkylation of benzyl-resorufin, a cytochrome P450-mediated activity, with the same specificity profile as for inhibition of CCE. These results are consistent with previous proposals suggesting that a microsomal cytochrome P450 may be involved in the regulation of CCE.

Octanoate increases cytosolic Ca2+ concentration and membrane conductance in ovine pancreatic acinar cells

In order to investigate the cellular mechanisms involved in amylase release in response to stimulation with short-chain fatty acids, changes in intracellular calcium concentration ([Ca2+]i), membrane current and amylase release were measured in pancreatic acinar cells of sheep. Both octanoate and acetylcholine raised [Ca2+]i in acinar cells in a concentration-dependent manner. The rise in [Ca2+]i in response to the stimulation with octanoate (10 mmol.l-1) was reduced in a medium without CaCl2, but was markedly enhanced by reintroduction of CaCl2 into the medium up to 2.56 mmol.l-1. Perfusion of the cells with a medium containing octanoate (5 mmol.l-1) or acetylcholine (0.5 mumol.l-1) immediately raised inward current across the cell membrane at a holding-membrane potential of -30 mV. The inward current became greater as the holding potential became more negative. The equilibrium potential was 1.8 mV and 3.9 mV for octanoate and acetylcholine, respectively, being consistent with that for Cl-. Although intracellular application of octanoate through a patch-clamp pipette also raised inward current after several minutes in some cells (4 out of 12), this possibility was significantly smaller than that for extracellular application. In other cells, even though the intracellular application of octanoate did not cause an increase in current, it always caused responses immediately after introduction of the fatty acid into the medium. Stimulation with fatty acid as well as acetylcholine raised amylase release in a concentration-dependent manner in cells dispersed from tissue segments with crude collagenase and trypsin inhibitor. Without trypsin inhibitor, crude collagenase significantly and selectively reduced the octanoate (10 mmol.l-1)-induced amylase release. Dispersion with crude collagenase and trypsin significantly reduced both responses induced by octanoate and acetylcholine (5.5 mumol.l-1). We conclude that fatty acids and acetylcholine increase [Ca2+]i, which consequently evokes a rise in transmembrane ion (Cl-) conductance and amylase release, and that trypsin-sensitive protein(s) in the cell membrane are involved in secretory processes activated by stimulation with fatty acids in ovine pancreatic acinar cells.