Volatile anesthetics affect calcium mobilization in bovine endothelial cells

Delayed treatment with isoflurane attenuates lipopolysaccharide and interferon gamma-induced activation and injury of mouse microglial cells

BACKGROUND

Isoflurane pretreatment can induce protection against lipopolysaccharide and interferon gamma (IFNgamma)-induced injury and activation of mouse microglial cells. This study's goal was to determine whether delayed isoflurane treatment is protective.

METHODS

Mouse microglial cells were exposed to various concentrations of isoflurane for 1 h immediately after the initiation of lipopolysaccharide (10 or 1000 ng/ml) and IFNgamma (10 U/ml) stimulation or to 2% isoflurane for 1 h at various times after initiation of the stimulation. Nitrite production, lactate dehydrogenase release, and cell viability measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay were assessed after stimulation with lipopolysaccharide and IFNgamma for 24 h. Inducible nitric oxide synthase (iNOS) protein expression was quantified by Western blotting. The iNOS expression in mouse brain was also studied.

RESULTS

Isoflurane applied 0 and 2 h after the initiation of lipopolysaccharide and IFNgamma stimulation improved cell viability. Isoflurane at 2%, but not at 1 or 3%, reduced the lipopolysaccharide and IFNgamma-induced nitrite production and decreased cell viability. Aminoguanidine, an iNOS inhibitor, also attenuated this decreased cell viability. Chelerythrine and bisindolylmalemide IX, protein kinase C inhibitors, abolished isoflurane effects on cell viability and iNOS expression after lipopolysaccharide and IFNgamma application. Isoflurane also decreased lipopolysaccharide-induced iNOS expression in mouse brain. Late isoflurane application to microglial cells reduced lipopolysaccharide and IFNgamma-induced lactate dehydrogenase release that was not inhibited by aminoguanidine.

CONCLUSIONS

These results suggest that delayed isoflurane treatment can reduce lipopolysaccharide and IFNgamma-induced activation and injury of microglial cells. These effects may be mediated by protein kinase C.

Inhibition of the histamine-induced Ca2+ influx in primary human endothelial cells (HUVEC) by volatile anaesthetics

BACKGROUND AND OBJECTIVE

Vasoactive substances such as histamine, acetylcholine or ATP increase the [Ca2+]i of endothelial cells, which leads to the activation of nitric oxide synthase (eNOS). The NO produced by this enzyme relaxes the underlying smooth muscle. Evidence suggests that eNOS activation is dependent on agonist-induced Ca2+ entry. Recently we have shown that in human endothelial cells (HUVEC), this Ca2+ entry is sensitive to isoflurane. The objective here was to study the mechanism by which volatile anaesthetics can depress the histamine-induced Ca2+ entry into HUVEC cells.

METHODS

HUVECs on coverslips were loaded with the Ca2+ indicator Fluo-3 and inserted in a gastight, temperature-controlled perfusion chamber. Excitation was at 488 nm and fluorescence signals were monitored with a confocal laser scanning microscope (MRC1024, Biorad). Direct measurement of the Ca2+ influx was with Mn2+ as surrogate for calcium at 360 nm in cells loaded with Fura-2.

RESULTS

Addition of histamine induces a biphasic [Ca2+]i increase consisting of Ca2+ release from internal stores and a Ca2+ influx from the external medium (plateau phase). The plateau phase was dose-dependently inhibited by enflurane and sevoflurane (13.7 resp. 21.9% inhibition by 1 MAC anaesthetic). Direct measurement of the Ca2+ influx using the Mn2+ quench of the Fura-2 fluorescence gave similar results. The inhibition of the anaesthetics was not reduced by inhibition of the cGMP pathway, inactivation of protein kinase C, depolarization of the cells or the presence of specific Ca2+-dependent K+ channel inhibitors. Interestingly, unsaturated fatty acids inhibit the histamine-induced Ca2+ influx in a similar way as the volatile anaesthetics.

CONCLUSIONS

Volatile anaesthetics dose-dependently inhibit the histamine-induced Ca2+ influx in HUVECs by a mechanism that may involve unspecific perturbation of the lipid bilayer.

Multiple actions of halothane on contractile response to noradrenaline in isolated mesenteric resistance arteries

Halothane, a volatile anaesthetic, produces systemic hypotension and significantly alters organ blood flow. Isometric force was recorded in isolated rat small mesenteric arteries to investigate its action on contractile response to noradrenaline, the sympathetic neurotransmitter. Halothane (1-5%) enhanced contractile response to noradrenaline in the endothelium-intact arteries, but had little influence in the endothelium-denuded arteries. However, halothane consistently inhibited the noradrenaline response in the endothelium-denuded arteries pretreated with ryanodine (10 microM). The enhancement of the contractile response to noradrenaline in the endothelium-intact arteries was unaffected by treatment with N(G)-nitro L-arginine, tetraethylammonium, apamin, charybdotoxin, indomethacin, diclofenac, nordihydroguaiaretic acid, BQ-123, BQ-788, losartan, ketanserin, or superoxide dismutase. Halothane prolonged vasorelaxation after washout of noradrenaline in the endothelium-denuded arteries. Both ryanodine and vanadate (0.1-0.3 mM), a putative inhibitor of the plasma membrane Ca2+-ATPase, also prolonged the vasorelaxation. Halothane still prolonged the vasorelaxation in the ryanodine-treated arteries, but not in the vanadate-treated arteries. Halothane decreased the pD2 value for the pCa-force relation in the beta-escin-permeabilised, endothelium-denuded arteries. Halothane appears to influence contractile response to noradrenaline through multiple actions including endothelium-dependent enhancing, endothelium-independent enhancing, and endothelium-independent inhibitory actions. Nitric oxide, endothelium-derived hyperpolarising factor, cyclooxygenase products, lipoxygenase products, endothelin-1, angiotensin-II, serotonin, and superoxide anions are not involved in the endothelium-dependent enhancement. The endothelium-independent enhancement is presumably due to its ability to stimulate Ca2+ release from the ryanodine-sensitive intracellular stores, while the endothelium-independent inhibition is due, at least in part, to depressed Ca2+-activation of contractile proteins. Halothane may inhibit the plasma membrane Ca2+-ATPase of vascular smooth muscle cells.

Effects of General Anesthetics on Regulation of the Peripheral Vasculature

The heart is a passively filling pump in a circulatory system that is connected in series with distensible blood vessels. Therefore, systemic blood pressure and tissue perfusion depend upon adequate peripheral vascular tone as well as myocardial function. Likewise, pharmacologic agents that alter circulatory stability can affect one or both of these components. The generalized depressor effects of general anesthetics have been well known clinically for over 50 years. Moreover, there are many similarities in basic cellular regulatory mechanisms among the different tissue types, and general anesthetics are well known to distribute freely among the perfusion-rich tissues (eg, central nervous system, cardiovascular system, and renal system). Therefore, it is likely that the hemodynamic depression resulting from the systemic administration of anesthetics results from actions on regulatory mechanisms of the peripheral vasculature as well as on the heart. The peripheral vasculature is regulated by extrinsic neural, endothelial, and humoral mechanisms, which interact with each other as well as with intrinsic membrane and intracellular systems within the vascular smooth muscle cell. Different general anesthetics have been found to act on specific mechanisms at each of these levels. However, the large number and complexity of these known mechanisms, as well as the many anesthetic agents, has made it extremely difficult to determine which are significant in terms of the meaningful mechanisms that are responsible for anesthetic action, major side effects, or both. Current knowledge about the effects of general anesthetics on both the extrinsic intrinsic regulatory mechanisms of peripheral vascular control is reviewed.

The volatile anesthetic isoflurane inhibits the histamine-induced Ca2+ influx in primary human endothelial cells

Although isoflurane is a known vasodilator, the mechanism of isoflurane-induced vasodilation is not clear. One of the most important systems in this context is the nitric oxide (NO)-mediated vasodilation. The activity of this system is regulated by the agonist-induced Ca(2+) influx rather than Ca(2+) release from internal stores. A number of reports have studied the effect of volatile anesthetics on the cytoplasmic calcium concentration signaling in mammalian endothelial cells. However, similar studies using human endothelial cells are lacking. In this study, therefore, we investigated whether isoflurane affects the histamine-induced Ca(2+) influx in primary cultures of human endothelial cells. Using confocal laser scanning microscopy and cells loaded with the Ca(2+) indicator Fluo-3, we studied the effect of isoflurane on the plateau phase of the histamine-induced Ca(2+) influx, which is considered to be due to capacitative Ca(2+) entry. In addition, we measured the ion flux through capacitative Ca(2+) channels directly by using Mn(2+) ions, which, on entering the cell, quench the Fura-2 fluorescence. The results of these two methods were in close agreement and showed a dose-dependent inhibition of the capacitative Ca(2+) entry by isoflurane. Isoflurane apparently depresses NO-mediated vasodilation when the observed inhibition is not compensated for downstream of the endothelial NO synthase activation.

IMPLICATIONS

In response to vasoactive agents, endothelial cells produce nitric oxide (NO), which relaxes the underlying smooth muscle cells. Inhaled anesthetics inhibit this system by an unknown mechanism. Using primary human endothelial cells, we showed that the anesthetic isoflurane depresses a Ca(2+) influx, which is responsible for the activation of the endothelial NO synthase.

Emprego do propofol, isofluorano e morfina para a anestesia geral de longa duração em bezerros

Foram estudadas características da bioquímica do sangue, da pressão arterial e da freqüência de pulso de 12 bezerros mantidos sob anestesia por 13 horas, utilizando-se propofol para a indução e isofluorano para manutenção, associados à administração de morfina intra-tecal. Os valores de freqüência de pulso, pressão arterial e glicemia apresentaram pequenas variações e se mantiveram próximos dos valores de referência para bezerros anestesiados. Ao longo do período de anestesia houve aumento significativo, mas discreto, do hematócrito, hemoglobina, pCO2, CO2 total, bicarbonato e potássio. O pH do sangue, pO2, Na+ e Ca++ apresentaram reduções significativas. Este protocolo anestésico foi seguro para a manutenção de bezerros anestesiados por período prolongado.

Sevoflurane and bradykinin-induced calcium mobilization in pulmonary arterial valvular endothelial cells in situ: sevoflurane stimulates plasmalemmal calcium influx into endothelial cells

Kinins locally synthesized in the cardiovascular tissue are believed to contribute to the regulation of cardiovascular homeostasis by stimulating the endothelial cells to release nitric oxide, prostacyclin, or a hyperpolarizing factor via autocrine-paracrine mechanisms. This study was designed to investigate the action of sevoflurane on bradykinin-induced Ca2+ mobilization in endothelial cells in situ. Utilizing fura-2-loaded rat pulmonary arterial valve leaflets, the effects of sevoflurane were examined on bradykinin-induced increases in intracellular Ca2+ concentration ([Ca2+]i) in endothelial cells in situ. In the presence of extracellular Ca2+ (1.5 mM), bradykinin (3-30 microM) produced an initial phasic and a subsequent tonic increase in [Ca2+]i in a concentration-dependent manner. However, it produced only the phasic increase in [Ca2+]i in the absence of extracellular Ca2+. Sevoflurane (5%, 0.67 mM) inhibited both the phasic and tonic responses to bradykinin. In these experiments, sevoflurane (3-5%) generated sustained increases (approximately 20-40% of the bradykinin-induced maximal increase in [Ca2+]i) in the resting [Ca2+]i level. Sevoflurane still increased [Ca2+]i after depletion of the intracellular Ca stores with ionomycin (0.1 microM ). However, the sevoflurane-induced increase in [Ca2+]i was eliminated by removal of the extracellular Ca and attenuated by NiCl (1-3 mM). In conclusion, in the pulmonary arterial valvular endothelial cells, sevoflurane inhibits both bradykinin-induced Ca2+ release from the intracellular stores and bradykinin-induced plasmalemmal Ca2+ influx. In addition, sevoflurane appears to stimulate the plasmalemmal Ca2+ influx and thereby increase the endothelial [Ca2+]i level. Sevoflurane might influence the pulmonary vascular tone through its direct action on the pulmonary arterial valvular endothelial cells.

Effect of hypoxia on parathyroid hormone in lactating and neonatal rats: interaction with halothane

Low oxygen in the blood (hypoxemia) may occur in the neonate or women in the postpartum period. Administration of inhalation anesthetic may be required in this period. The purpose of this study was to evaluate the effect of 7 d of hypoxia on the neonatal rat pup and lactating dam without or with acute halothane anesthesia on serum calcium and calciotropic hormones. Ionized calcium was not altered by hypoxia or halothane administration. Hypoxia from birth had no effect on serum parathyroid hormone (PTH) in 7-d-old rat pups (48+/-4 pg/mL). Halothane increased PTH in rat pups (74+/-8 pg/mL). The effect of halothane was not augmented in hypoxic pups. Hypoxia for 7 d had no effect on serum PTH in lactating dams (23+/-3 pg/mL). Halothane resulted in an increase in PTH (106+/-17 pg/mL). When halothane was administered to hypoxic lactating dams, a striking increase in serum PTH was observed (401+/-50 pg/mL). We hypothesize that halothane and hypoxia alter parathyroid gland function by a direct effect on cellular calcium dynamics. This interaction may have clinical significance in hypoxic patients requiring general anesthesia.

The effect of halothane and isoflurane on plasma cytokine levels

The aim of this study was to investigate the effect of halothane vs. isoflurane on cytokine production during minor elective surgery. Forty adult patients, ASA I-II were randomly allocated to receive halothane or isoflurane. Venous samples for interleukin (IL)-1beta, IL-2, IL-6, tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) were taken before anaesthesia, before incision, at the end of anaesthesia and 24 h postoperatively. In both groups, IL-6 and TNF-alpha levels remained low throughout the study period. Before incision, in both groups IL-1beta and IFN-gamma showed a decrease (p<0.01 for IL-1beta in isoflurane group and p<0.05 for the others) compared with pre-induction. By the end of anaesthesia and surgery, IL-1beta had increased significantly (p<0.05) and IFN-gamma had decreased significantly (p<0.05) in both groups compared with pre-incisional levels. By 24 h postoperatively in both groups, IL-1beta had decreased significantly (p<0.05), whereas IFN-gamma had increased significantly (p<0.05) compared with the end of anaesthesia and surgery level. Pre-incisionally, IL-2 increased in the halothane group (p<0.01), whereas it decreased significantly in the isoflurane group (p<0.001) compared with the pre-induction level. By the end of anaesthesia and surgery and by 24 h postoperatively, IL-2 had decreased significantly in the halothane group (p<0.001), whereas it increased significantly in the isoflurane group (p<0.001) compared with pre-incision and end of anaesthesia and surgery levels, respectively.

Effect of sevoflurane on Ca2+ mobilization in Madin-Darby canine kidney cells

We investigated the effect of the volatile anesthetic sevoflurane on Ca2+ signaling in Madin-Darby canine kidney (MDCK) cells by using the fluorescent dye fura-2/AM (1-[2-(5-carboxyoxazol-2-yl)-6-aminobenzofuran-5-oxy]-2-(2'-amino-5'-methylphenoxy)-ethane-N,N,N,N-tetraacetic acid pentaace-toxymethyl ester) as the Ca2+ indicator. At a concentration of 0.15 mM, sevoflurane did not alter basal cytosolic free calcium concentration ([Ca2+]i); however, at concentrations of 0.45-0.6 mM, sevoflurane did elevate [Ca2+]i, mainly by releasing Ca2+ from the endoplasmic reticulum (ER) store. Sevoflurane (0.15 mM) did not change either the [Ca2+]i peak evoked by high doses of ATP or UTP or inhibition of the ER Ca2+ pump, although it did significantly slow down the decay of the [Ca2+]i rise. Lastly, sevoflurane inhibited the capacitative Ca2+ entry and Mn2+ quench of fura-2 fluorescence induced by Ca(2+)-mobilizing ligands.

Halothane and isoflurane attenuate the relaxant response to nonadrenergic and noncholinergic nerve stimulation of isolated canine cerebral arteries

Stimulation of nonadrenergic noncholinergic (NANC) nerves elicits relaxation of canine cerebral arteries via the nitric oxide (NO)-cGMP pathway. The purpose of this study was to investigate the effects of halothane and isoflurane on the relaxant response of isolated canine cerebral arteries to NANC nerve stimulation. The isometric tension of isolated canine cerebral arteries, which had been denuded of endothelium, was measured in a tissue bath. The application of transmural electrical stimulation (TES) at a frequency of 5 Hz elicited a transient relaxation of arteries partially contracted with prostaglandin F2alpha. This effect was abolished by treatment with N(G)-nitro-L-arginine (3 x 10[-5] M), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10[-5] M), or tetrodotoxin (10[-6] M). Treatment with halothane (2.3%) or isoflurane (2.3% and 3.5%) attenuated the relaxant response to TES (P < 0.05). Halothane (2.3%) but not isoflurane (2.3% and 3.5%) attenuated relaxation induced by s-nitro-N-acetylpenicillamine. We suggest that halothane and isoflurane inhibit cerebroarterial vasodilation mediated via NO-cGMP pathway activated by stimulation of the NANC nerves. The sites of action of halothane and isoflurane on the NO-cGMP pathway may differ.

IMPLICATIONS

Nonadrenergic noncholinergic nerves play a role in the regulation of vascular tone in cerebral arteries via the nitric oxide-cGMP pathway. This study showed that, in isolated canine cerebral arteries, halothane and isoflurane inhibit the relaxation caused by nonadrenergic noncholinergic nerve stimulation, but their sites of action may differ.