Calmodulin stimulates human platelet phospholipase A2

Anthocyanin extract from black rice significantly ameliorates platelet hyperactivity and hypertriglyceridemia in dyslipidemic rats induced by high fat diets

Our previous studies have demonstrated that anthocyanin extract from black rice (AEBR) inhibits atherosclerosis. Whether dietary AEBR supplementation can affect platelet function, an important factor in the pathogenesis of cardiovascular diseases, remains unclear. The aim of the present study is to explore the effects and mechanisms of dietary AEBR supplementation on platelet function and lipid profile in dyslipidemic rats. We demonstrated herein that thromboxane A(2), the thrombogenic ratio of thromboxane A₂ and prostacyclin, serum calmodulin, and soluble P-selectin were significantly decreased in rats fed a high fat diet supplemented with AEBR. AEBR supplementation also remarkably lowered serum triglyceride and raised hepatic CPT-1 mRNA expression. These findings suggest that dietary intake of AEBR reduces platelet hyperactivity, hypertriglyceridemia, and body weight gain, and facilitates in the maintenance of optimal platelet function in dyslipidemic rats induced by high fat diets.

Regulation of pulmonary arachidonic acid metabolism by anti-inflammatory steroids

Enzymes in cells from many tissues including the lung metabolize arachidonic acid to a variety of highly active local hormones such as prostaglandins and 'slow-reacting substances'. Many of these play a part in the inflammatory response which follows injury or trauma or, in the case of slow-reacting substance, asthmatic bronchoconstriction. Both non-steroidal and steroidal anti-inflammatory drugs inhibit the formation of some or all of these products. The non-steroidal drugs block prostaglandin formation but not the formation of products such as slow-reacting substances. The steroids block the formation of all products. Their mechanism of action, investigated in the guinea-pig perfused lung, involved inhibition of arachidonic acid liberation, probably by suppression of phospholipase activity. To achieve this steroids must first bind to receptors in lung tissue and initiate de novo RNA and protein synthesis. This culminates in the synthesis or secretion by some cells in the lung of a polypeptide of mol.wt. 10 000-15 000 with potent anti-phospholipase properties. The generation of this factor could partly explain why steroids are so effective in the treatment of many types of inflammatory disease, and in particular why they are so efficacious against asthma.

Effects of prostaglandin E2 and progesterone on rat brain synaptosomal plasma membranes

The lipid fluidity of rat brain synaptosomal plasma membranes (SPM) labelled with 1,6-diphenyl-1,3,5-hexatriene (DPH) was increased by prostaglandin E2 (PGE2) and decreased by progesterone, as indicated by steady-state fluorescence anisotropy [(ro/r)-1]-1. Arrhenius-type plots of [(ro/r)-1]-1 indicated a lipid phase separation of SPM at approximately 23.5 degrees C which was reduced to approximately 18.1 degrees C by PGE2 and increased to approximately 34.6 degrees C by progesterone. Treatment of SPM by PGE2 and progesterone caused an increase of the lipid phase separation to approximately 32.4 degrees C. Arrhenius plots of Na+/K(+)-ATPase activity in control SPM exhibited a break point at approximately 23.1 degrees C which was reduced to approximately 17.8 degrees C by PGE2 and increased to approximately 32.6 degrees C by progesterone. SPM treated with PGE2 plus progesterone showed an increased break point at approximately 29.3 degrees C. Na+/K(+)-ATPase activity was increased at a PGE2 concentration range between 0.1 and 3 microM; higher concentrations (up to 10 microM) led to a gradual inhibition of enzyme activity. Progesterone (0.1-10 microM) and PGE2 plus progesterone both produced a gradual decrease in enzyme activity. The allosteric inhibition of Na+/K(+)-ATPase by fluoride (F-) (as reflected by changes in the Hill coefficient) was modulated by PGE2 and progesterone. The perturbations of membrane lipid structure and changes in membrane fluidity provide a basis for suggesting an independent non-genomic mechanism for the progesterone-induced alterations in the effects of PGE2 on brain function.

Calcium: a potential central regulator in wound healing in the skin

Calcium has an established role in the normal homeostasis of mammalian skin and serves as a modulator in keratinocyte proliferation and differentiation. Gradients of calcium concentration increasing from 0.5 mM in the basal layer to > 1.4 mM in the stratum granulosum are consistent with migration patterns in response to minor abrasion (normal wear). Dermal fibroblasts require calcium but are approximately 100 times less sensitive than keratinocytes. Normal calcium metabolism in the skin is dependent on cell membrane and cytosolic calcium binding proteins (calmodulin, cadherins, etc.), but their modulation through parathyroid hormone, vitamin D or growth factors in normal or damaged tissue is not well documented. In wound repair, calcium is predominantly involved as Factor IV in the hemostatic phase, but it is expected to be required in epidermal cell migration and regeneration patterns in later stages of healing. Calcium alginate dressings are designed to liberate calcium early in the acute phase to promote hemostasis, but it is presently unclear whether the supplementary calcium influences the intracellular environment at later stages of wound repair, notably during the remodeling phase. Although experimental studies suggest that control of calcium is obligatory in wound management, we know very little as to how calcium in the wound bed is modulated through hormones, vitamin D, or various growth factors. Also, there is limited information as to how calcium released either from dressings, platelets, or from the circulation through the action of parathyroid hormone, growth factors or other modulators influences cell migration and remodeling in skin wounds, although experimental models suggest that management of calcium is essential in wound management.

The effects of various organ preservation solutions on hepatocyte membrane potentials, intracellular calcium concentrations, and outcome following liver transplantation

BACKGROUND

Hepatocyte membrane potential differences (PDs) may be altered by the preservation solutions used in liver transplantation. Such alterations could impact on the survival of the donor liver, extent of biochemical injury, and flux of important ionic compounds. The purpose of the present study was to document these outcomes in the presence of four different preservation solutions.

METHODS

Livers of adult male Sprague-Dawley rats (N = 3 to 4 per group) were impaled with intracellular microelectrodes prior to and at various time periods for 6 hours following complete hepatic resection. Just prior to resection, each liver was perfused with preservation solutions associated with high (normal saline [NS]), moderate (Euro-Collins [EC]), and low (University of Wisconsin solution [UW]) risks of reperfusion injury.

RESULTS

Baseline (in situ) PDs were similar in all groups (-37 +/- 4 mV, mean +/- SD). Ten minutes postresection, hepatic PDs were as follows: NS, -23.8 +/- 3.5 mV; EC, -11.4 +/- 0.4 mV; and UW, -8.7 +/- 0.3 mV (P <0.01 for all groups). Maximum depolarization occurred at 6 hours postresection (NS, -8.1 +/- 1.1 mV; EC, -7.7 +/- 1.3 mV; and UW, -8.6 +/- 1.0 mV). To determine whether these changes are of pathophysiologic importance, the NS solution was modified (addition of 0.1% ethanol) to achieve similar PD changes as those observed with UW. Liver transplants were then performed where the donor livers had been perfused and preserved for 6 hours with either NS or the modified NS (MNS) solution. Posttransplant (10 day) survival was 1 of 6 (17%) in the NS group and 4 of 6 (67%) in the MNS group (P <0.05). Regarding the effects of PD changes on ionic flux, intracellular calcium levels were documented for up to 4 hours by fluorescence video microscopy using Fura-2 in isolated hepatocytes exposed to NS, UW, and MNS solutions. Intracellular calcium levels were similar in all solutions at each time point studied.

CONCLUSIONS

The results of this study indicate that hepatocytes undergo prompt and marked depolarization following hepatic resection, and the extent of the depolarization correlates with survival following transplantation.

Effects of KW-5617 (zaldaride maleate), a potent and selective calmodulin inhibitor, on secretory diarrhea and on gastrointestinal propulsion in rats

KW-5617 (zaldaride maleate), 1,3-dihydro-1-[1-[(4-methyl-4H,6H-pyrrolo[1,2-a][4,1]-benzoxazepin -4-yl)methyl]-4-piperidinyl]-2H-benzimidazol-2-one maleate, is a selective calmodulin inhibitor. We studied the effects of KW-5617 on secretory diarrhea and gastrointestinal propulsion in rats, as compared with those of loperamide, a conventional anti-diarrheal drug. Diarrhea was induced in rats either by 16,16-dimethyl prostaglandin E2 (500 microg/kg, i.p.) or by castor oil (1 ml/100 g body weight, p.o.). In the 16,16-dimethyl prostaglandin E2 model, KW-5617 at the doses of 3 mg/kg (p.o.) and higher ameliorated the diarrhea. Similarly, loperamide improved the diarrhea, the activity of loperamide being equivalent to that of KW-5617. In the castor oil model, KW-5617 significantly delayed the onset of diarrhea at the doses of 3 mg/kg (p.o.) and higher, while loperamide delayed the onset of diarrhea at the doses of 0.3 mg/kg (p.o.) and higher. KW-5617 only at the high doses of 30 and 100 mg/kg (p.o.) reduced gastric emptying, small intestinal propulsion, proximal colonic propulsion and distal colonic propulsion. In contrast, loperamide at its anti-diarrheal doses inhibited gastrointestinal propulsion. Our results show that KW-5617, unlike loperamide, at its anti-diarrheal doses does not exert anti-propulsive effects in rats. KW-5617 may be a useful drug for the treatment of diarrhea in terms of less side effects such as constipation.

Oxidative stress-mediated neurotoxicity of cadmium

Young albino rats were administered cadmium i.p. (0.4 mg/kg body weight) for a period of 30 days and membrane fluidity, intracellular calcium level, MDA level, phospholipids, (phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol, phosphatidylserine and sphingomyelin) and reduced glutathione were studied in olfactory bulb, cerebellum and rest of brain. A decrease in membrane fluidity was observed in all the brain regions studied, maximum being in olfactory bulb (21%). Intracellular calcium (Ca+2)i level was increased significantly in olfactory bulb (150%) followed by rest of brain (98%) and cerebellum (71%) in Cd-exposed rats in comparison with controls. A significant decrease in phosphatidylcholine (27%) and phosphatidylethanolamine (22%) was observed in olfactory bulb, while other phospholipids remained unaffected. TBA reactivity was increased in olfactory bulb (77%), cerebellum (35%) and rest of brain (27%). Reduced glutathione level was also decreased in different brain regions. The results suggest that the effect of cadmium in brain is region-specific and most pronounced in olfactory bulb.

Mn(2+)-induced transient contraction of the longitudinal muscle of guinea-pig stomach through prostaglandin synthesis

1. A low concentration of Mn2+ (less than 0.3 mM) transiently enhanced a contractile force (Mn(2+)-induced TC) of the longitudinal muscles of the guinea-pig stomach. 2. The Mn(2+)-induced transient contraction (TC) was not blocked by TTX (10(-7) M) or atropine (10(-6) M), nor by nifedipine (10(-6) M) or D-600 (10(-6) M), but was blocked by Ca2+ removal from the Krebs solution. 3. A preapplication of indomethacin (10(-7) M) completely inhibited an induction of the Mn(2+)-induced TC, but exogenous PGE2 (10(-7) M) was able to induce Mn(2+)-induced TC even with the presence of indomethacin (10(-7) M) and Mn2+ (0.1 mM) in the Krebs solution. 4. Quinacrine (10(-5) M), a phospholipase A2 inhibitor, partially inhibited the Mn(2+)-induced TC. 5. These results suggest that Mn(2+)-induced TC is probably mediated through cyclooxygenase and the subsequent generation of prostaglandin leading to the contraction.

The role of elevations in intracellular [Ca2+] in the development of low frequency fatigue in mouse single muscle fibres

1. Intracellular free calcium concentration ([Ca2+]i) and force were measured in isolated single skeletal muscle fibres from mice. The aim was to determine the extent to which elevations in [Ca2+]i during various stimulation protocols affected subsequent muscle performance. 2. A protocol of repeated tetanic stimulation which elevated [Ca2+]i and caused a large decline in force (fatigue) had a [Ca2+]-time integral of 36.4 +/- 8.1 microM s. A protocol of repeated tetani at a lower duty cycle (stimulation) caused only a small decline in force (9-16%) but elevated the [Ca2+]-time integral to 16.7 +/- 2.8 and 24.9 +/- 1.6 microM s in the absence and presence of 10 mM caffeine, respectively. Caffeine alone raised the [Ca2+]-time integral to 20.3 +/- 3.4 microM s. 3. Following the fatigue protocol there was a proportionately greater loss of force at low stimulation frequencies (30 and 50 Hz) compared with high frequencies (100 Hz) which persisted for up to an hour. This pattern of force loss could be attributed to a uniform reduction in [Ca2+]i at all frequencies. Similar effects were observed after elevating [Ca2+]i with the caffeine + stimulation protocol but were not observed after stimulation or caffeine alone. The higher [Ca2+]-time integrals during the fatigue and caffeine + stimulation protocols suggest that some threshold for [Ca2+]i must be reached before these effects are observed. 4. The reductions in low frequency force induced by the fatigue and caffeine + stimulation protocols were not due to decreased Ca2+ sensitivity or to decreases in maximum force-generating capacity of the contractile proteins and therefore are due to a failure of Ca2+ release. 5. The Ca(2+)-activated neutral protease (calpain) inhibitor calpeptin was not effective in preventing the effects of caffeine + stimulation indicating that the reduction in Ca2+ release was not due to calpain-mediated hydrolysis of the Ca2+ release channel. 6. Our findings indicate that low frequency fatigue results from increases in [Ca2+]i during fatigue and that these elevations in [Ca2+]i activate some process which leads to failure of excitation-contraction (E-C) coupling and Ca2+ release.

Membrane mechanisms and intracellular signalling in cell volume regulation

Recent work on selected aspects of the cellular and molecular physiology of cell volume regulation is reviewed. First, the physiological significance of the regulation of cell volume is discussed. Membrane transporters involved in cell volume regulation are reviewed, including volume-sensitive K+ and Cl- channels, K+, Cl- and Na+, K+, 2Cl- cotransporters, and the Na+, H+, Cl-, HCO3-, and K+, H+ exchangers. The role of amino acids, particularly taurine, as cellular osmolytes is discussed. Possible mechanisms by which cells sense their volumes, along with the sensors of these signals, are discussed. The signals are mechanical changes in the membrane and changes in macromolecular crowding. Sensors of these signals include stretch-activated channels, the cytoskeleton, and specific membrane or cytoplasmic enzymes. Mechanisms for transduction of the signal from sensors to transporters are reviewed. These include the Ca(2+)-calmodulin system, phospholipases, polyphosphoinositide metabolism, eicosanoid metabolism, and protein kinases and phosphatases. A detailed model is presented for the swelling-initiated signal transduction pathway in Ehrlich ascites tumor cells. Finally, the coordinated control of volume-regulatory transport processes and changes in the expression of organic osmolyte transporters with long-term adaptation to osmotic stress are reviewed briefly.

Down-regulation of protein kinase C attenuates the oxidant hydrogen peroxide-mediated activation of phospholipase A2 in pulmonary vascular smooth muscle cells

Exposure of rabbit pulmonary vascular smooth muscle cells to H2O2 dose-dependently stimulates the cell membrane associated protein kinase C (PKC) activity, phospholipase A2 (PLA2) activity, phospholipase A2 (PLA2) activity, and arachidonic acid (AA0) release. Pretreatment of the cells with staurosporine (an inhibitor of PKC) prevents AA release and PLA2 activity caused by H2O2. Treatment of the cells with 4 beta-PMA (an active phorbol ester), or 4 alpha-PMA (an inactive phorbol ester) does not affect basal AA release. In contrast, 4 beta-PMA significantly stimulates the cell membrane associated PKC activity. Treatment of the cells with 4 beta-PMA for a short time (up-regulation of PKC) augments PLA2 activity and AA release caused by a sub-optimal dose of H2O2 (0.4 mM). Under this condition, staurosporine prevents the stimulatory effects of 4 beta-PMA on membrane PLA2 activity, and AA release. In contrast to the up-regulation, pretreatment with 4 beta-PMA for a longer time (down-regulation of PKC) does not appreciably augment PLA2 activity and AA release caused by 0.4 mM H2O2. Treatment of the cells with an intracellular Ca2+ antagonist TBM-8 prevents H2O2 induced membrane PLA2 activity and AA release without affecting membrane PKC activity. Treatment of the cells with TMB-8 before addition of 4 beta-PMA (up-regulation of PKC) followed by incubation with 0.4 mM H2O2 does not augment PLA2 activity and AA release, although membrane PKC activity increases under this condition.

Permissive stimulation of Ca(2+)-induced phospholipase A2 by an adenosine receptor agonist in a pertussis toxin-sensitive manner in FRTL-5 thyroid cells: a new 'cross-talk' mechanism in Ca2+ signalling

We have described the pertussis toxin (PTX)-sensitive potentiation of P2-purinergic agonist-induced phospholipase C activation, Ca2+ mobilization and arachidonic acid release by an adenosine receptor agonist, N6-(L-2-phenylisopropyl)adenosine (PIA), which alone cannot influence any of these cellular activities [Okajima, Sato, Nazarea, Sho and Kondo (1989) J. Biol. Chem. 264, 13029-13037]. In the present study we have found that arachidonic acid release was associated with lysophosphatidylcholine production, and conclude that arachidonic acid is produced by phospholipase A2 in FRTL-5 thyroid cells. This led us to assume that PIA augments P2-purinergic arachidonic acid release by increasing [Ca2+]i which, in turn, activates Ca(2+)-sensitive phospholipase A2. The arachidonic acid-releasing response to PIA was, however, always considerably higher (3.1-fold increase) than the Ca2+ response (1.3-fold increase) to the adenosine derivative. In addition, arachidonic acid release induced by the [Ca2+]i increase caused by thapsigargin, an endoplasmic-reticulum Ca(2+)-ATPase inhibitor, or calcium ionophores was also potentiated by PIA without any effect on [Ca2+]i and phospholipase C activity. This action of PIA was also PTX-sensitive, but not affected by the forskolin- or cholera toxin-induced increase in the cellular cyclic AMP (cAMP), suggesting that a PTX-sensitive G-protein(s) and not cAMP mediates the PIA-induced potentiation of Ca(2+)-generated phospholipase A2 activation. Although acute phorbol ester activation of protein kinase C induced arachidonic acid release, P2-purinergic and alpha 1-adrenergic stimulation of arachidonic acid release was markedly increased by the protein kinase C down-regulation caused by the phorbol ester. This suggests a suppressive role for protein kinase C in the agonist-induced activation of arachidonic acid release. We conclude that PIA (and perhaps any of the G1-activating agonists) augments an agonist (maybe any of the Ca(2+)-mobilizing agents)-induced arachidonic acid release by activation of Ca(2+)-dependent phospholipase A2 in addition to enhancement of agonist-induced phospholipase C followed by an increase in [Ca2+]i.

Calcium signalling in platelets and other nonexcitable cells

By virtue of their biological simplicity and widespread availability, platelets frequently have been used as a model system to study signal transduction. Such studies have revealed that changes in intracellular free calcium concentration are central to platelet functioning. The following article reviews current concepts of platelet structure and function, with particular emphasis on the mechanisms involved in platelet Ca2+ signalling.

Roles of Ca2+ and protein kinase C in regulation of prostaglandin E2 release by cultured rabbit gastric epithelial cells

Prostaglandin (PG) has been reported to be one of the important protective factors in the gastric mucosa. However the mechanism of the regulation of endogenous PG production has not been well studied. We investigated the possible roles of Ca2+, cAMP, and protein kinase C (PKC) in the regulation of PGE2 release from cultured rabbit gastric mucosal cells. PGE2 was measured by radioimmunoassay. A23187 (Ca2+ ionophore) at 2 x 10(-6) M significantly increased PGE2 release. Deprivation of Ca2+ from the medium blocked the A23187-induced increase of PGE2. TMB-8 (a putative inhibitor of Ca2+ release from intracellular stores) did not have any significant effects on the increase of PGE2-induced by A23187. Thus, A23187 increased PGE2 through the influx of extracellular Ca2+. W7 or compound 48/80 (calmodulin inhibitors) did not alter the response of PGE2 caused by A23187. Exogenous administration of cAMP, forskolin (an activator of adenylate cyclase), or 2-chloroadenosine (a possible activator of adenylate cyclase through adenosine A2 receptor) had neither significant effects on PGE2 release nor an effect on A23187-induced increase of PGE2 release. 12-O-tetradecanoylphorbol 13-acetate (TPA, an activator of PKC) significantly stimulated PGE2 release in a dose-dependent fashion, whereas another phorbol ester with no biological activity did not. A23187 at 0.8 x 10(-6) M, but not cAMP, potentiated the TPA-induced increase of PGE2. Mepacrine (a phospholipase A2 inhibitor) reduced the A23187- and TPA-induced increase of PGE2. These results suggest that Ca2+ and protein kinase C may play important roles in the regulation of PGE2 release by cultured rabbit gastric cells.

[125I]calmodulin binding to synaptic plasma membrane from rat brain: kinetic and Arrhenius analysis

Binding of [125I]calmodulin was characterized in highly purified synaptic plasma membrane (SPM) prepared from rat brain. By Scatchard analysis, the Ca(2+)-dependent membrane binding of [125I]calmodulin was found to have a Bmax of 284 pmol/mg protein and an apparent affinity with a Kd of 131 nM. Kinetic analysis indicates that at 37 degrees C, the dissociation of [125I]calmodulin-membrane complexes follows first-order reaction and consists of two components: a dissociation constant (k) of 3.7 x 10(-1) min-1 and a half-time (t1/2) of 1.8 min for the fast component, and a k of 4.8 x 10(-2) min-1 and a t1/2 of 14.5 min for the slow component. At 0 degrees C, substantial dissociation still occurred, with a k of 4.5 x 10(-2) min-1 and a t1/2 of 15.3 min for the fast component, and a k of 5.5 x 10(-3) min-1 and a t1/2 of 125.5 min for the slow component. These data on binding affinity and dissociation kinetics are consistent with the notion that SPM can readily and rapidly associate and dissociate calmodulin. In Arrhenius analysis of temperature effects, [125I]calmodulin binding to SPM exhibits a biphasic function, with the transition temperature (Td) estimated to be 23.8 degrees C, suggesting that binding is influenced by lipid phase transition of the membrane. The binding of [125I]calmodulin to the synaptic membrane was found to be increased by corticosterone (10(-7)-10(-6) M), a steroid hormone, and decreased by ethanol (50-200 mM), a centrally acting drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms by which extracellular ATP and UTP stimulate the release of prostacyclin from bovine pulmonary artery endothelial cells

Extracellular ATP and UTP caused increases in the concentration of cytoplasmic free calcium ([Ca2+]i) and the intracellular level of inositol 1,4,5-trisphosphate (IP3), a second messenger for calcium mobilization, prior to the release of prostacyclin (PGI2) from cultured bovine pulmonary artery endothelial (BPAE) cells. The agonist specificity and dose-dependence were similar for nucleotide-mediated increases in IP3 levels, [Ca2+]i and PGI2 release. An increase in [Ca2+]; and PGI2 release was observed after addition of ionomycin, a calcium ionophore, to BPAE cells incubated in a calcium-free medium. The addition of ATP to the ionomycin-treated cells caused no further increase in [Ca2+]i or PGI2 release. The inability of ATP to cause an increase in [Ca2+]i or PGI2 release in ionomycin-treated cells was apparently due to the ionomycin-dependent depletion of intracellular calcium stores since the subsequent addition of extracellular calcium caused a significant increase in both [Ca2+]i and PGI2 release. Introduction of BAPTA, a calcium buffer, into BPAE cells inhibited ATP-mediated increases in [Ca2+]i and PGI2 release, further evidence that PGI2 release is dependent upon an increase in [Ca2+]i. The increase in [Ca2+]i elicited by ATP apparently caused the activation of a calmodulin-dependent phospholipase A2 since trifluoperazine, an inhibitor of calmodulin, and quinacrine, an inhibitor of phospholipase A2, prevented the stimulation of PGI2 release by ATP. Furthermore, ATP caused the specific hydrolysis of [14C]arachidonyl-labeled phosphatidylcholine and the generation of free arachidonic acid, the rate-limiting substrate for PGI2 synthesis, prior to the release of PGI2 from BPAE cells. These findings suggest that the increase in PGI2 release elicited by ATP and UTP is at least partially dependent upon a phospholipase C-mediated increase in [Ca2+]i and the subsequent activation of a phosphatidylcholine-specific phospholipase A2. ATP analogs modified in the adenine base or phosphate moiety caused PGI2 release with a rank order of agonist potency of adenosine 5'-O-(2-thiodiphosphate) (ADP beta S) greater than 2-methylthioATP (2-MeSATP) greater than ATP, whereas alpha, beta methyleneATP and beta, gamma methyleneATP had no effect on PGI2 release.

Calmodulin antagonists chlorpromazine and W-7 inhibit exogenous cholesterol esterification and sphingomyelinase activity in human skin fibroblast cultures. Similarities between drug-induced and Niemann-Pick type C lipidoses

In this report we showed that calmodulin antagonists chlorpromazine (CPZ) and W-7 (N-[6-aminohexyl]-5-chloro-1-naphtalenesulfonamide), when added to fibroblast cell cultures, gave rise to a time- and dose-dependent decrease of sphingomyelinase activity. CPZ and W-7 also significantly inhibited LDL- and non-LDL-dependent cholesterol esterification. Addition of these drugs to cell culture medium mimicked what is observed in the genetic disease Niemann-Pick type C. H-7 (1-[5-isoquinonylsulfonyl]-2-methylpiperazine), an inhibitor of protein kinase C and cyclic nucleotide-dependent kinases, had no effect on sphingomyelinase and cholesterol ester formation. Thus the possibility of a modulation of cell sphingomyelin and cholesterol esters by a calmodulin-dependent second messenger system must be considered.

A study of the effects of p,p'-DDE and other related chlorinated hydrocarbons on inhibition of platelet aggregation

A series of chlorinated hydrocarbons of interest in environmental toxicology were investigated concerning their effects on human platelet aggregation. Most potent in inhibiting platelet aggregation were p,p'-DDE and Arochlor 1242. Aggregation induced by arachidonic acid (1 mM) was more sensitive to inhibition by p,p'-DDE than was aggregation induced by ADP (10 microM). The former was completely inhibited by p,p'-DDE at a concentration of 1 x 10(-4) M, whereas there was only a 31% inhibition of the latter. Addition of Ca2+ (1 mM) blocked the inhibitory effect of p,p'-DDE on aggregation induced by both arachidonic acid and ADP. Calmodulin (1 microgram/ml) blocked the inhibitory effect of p,p'-DDE on aggregation induced by arachidonic acid but not that induced by ADP. The calmodulin inhibitory drugs trifluoperazine and calmidazolium had no effect at all or only a weak effect (-14%), respectively, on platelet aggregation. Increasing the concentrations of p,p'-DDE and Arochlor 1242 caused a delay in the onset of aggregation induced by the addition of arachidonic acid. The synthesis of thromboxane B2 and other prostaglandins in platelet membranes was dose-dependently reduced by p,p'-DDE. The structurally closely related isomers o,p'-DDE and p,p'-DDT did not significantly inhibit arachidonic acid-induced platelet aggregation or thromboxane B2 synthesis. It is concluded that p,p'-DDE and Arochlor 1242 inhibited platelet aggregation by inhibiting platelet cyclooxygenase activity.

Two-step mobilization of arachidonic acid in platelet activation induced by low concentrations of TP 82, a monoclonal antibody against CD9 antigen

Arachidonic acid mobilization in platelets activated by low concentrations (less than or equal to 1.6 micrograms/ml) of TP 82, a monoclonal antibody against CD9, appears to consist of two distinct phases. In the first phase, limited arachidonic acid release occurs concomitantly with a shape change induced by TP 82. This appears to be dependent upon phospholipase A2 activation, since it is well preserved in the presence of aspirin, which completely blocked both intracellular Ca2+ elevation and phosphatidic acid formation which would indicate phospholipase C activation. The Na+ Exchange was also found to participate in the first phase of arachidonic acid mobilization, since extracellular Na+ depletion and ethylisopropylamiloride, a specific inhibitor of the Na+/H+ exchanger, effectively blocked this limited mobilization of arachidonic acid. The second, much larger, phase of arachidonic acid mobilization occurs with the beginning of platelet aggregation. A limited amount of thromboxane A2 formed during the first phase of arachidonic acid release plays an important role in induction of the massive arachidonic mobilization in the second phase. Factors, as yet unidentified, also appear to work synergistically with thromboxane A2 to induce the full picture of arachidonic acid mobilization.

Effects of calmodulin antagonists on sodium-dependent high-affinity choline uptake

The effects of calmodulin (CaM) antagonists were investigated on the sodium-dependent high-affinity choline uptake (SDHACU) as assessed by the specific binding of [3H]hemicholinium-3 ([3H]HCh-3) and high-affinity [3H]choline uptake. Potassium depolarization caused a significant 2-fold increase in the specific binding of [3H]HCh-3 in slices of rat striatum in vitro. CaM antagonists, including trifluoperazine (TFP), W-5, W-7, promethazine and haloperidol, dose-dependently inhibited potassium depolarization-stimulated [3H]HCh-3 binding with IC50s of 20, 40, 70, 30 and 48 (microM), respectively. Scatchard analysis revealed that the inhibitory effect of TFP resulted from a decrease in Bmax but no change in Kd of [3H]HCh-3 binding. Potassium depolarization of slices also stimulated high-affinity [3H]choline uptake, which was completely inhibited by 10 microM TFP. These results are discussed in relation to the regulatory mechanisms of SDHACU.

Phenothiazines inhibit collagen-induced thromboxane B2 synthesis and increase forskolin anti-aggregating effects in human platelets

1. The aim of the present study was to investigate the effects of phenothiazine compounds chlorpromazine and trifluoperazine on human platelet response to collagen and sodium arachidonate. 2. The results demonstrated that phenothiazines inhibit collagen-induced platelet aggregation and thromboxane B2 synthesis in a dose-dependent way and increase the antiaggregating properties of forskolin. 3. Phenothiazines at high concentrations decreased the platelet aggregation in response to arachidonate, without a significant reduction of thromboxane B2 production. 4. The data provides evidence that phenothiazine effects could involve calmodulin-dependent enzymatic activities.

Stimulation of phospholipase A2 activity in human platelets by trypsin and collagen

Type I collagen enhanced human platelet phospholipase A2 activity whether added to platelet-rich plasma or washed platelets. The stimulatory effect of type I collagen on platelet membrane phospholipase A2 activity was also observed in a cell-free system utilizing platelet membranes. The release of arachidonic acid was enhanced by types I and III but not by type V collagen. The activation of platelet phospholipase A2 by type I collagen was inhibited by soybean trypsin inhibitor and mimicked by trypsin. However, type I collagen addition was not associated with any detectable changes in platelet membrane proteins while trypsin altered many proteins. These results point to acid soluble phospholipase A2 activity of platelets as an enzyme activated by type I collagen.

Effect of the calmodulin antagonist CGS 9343B on skin burns

1. CGS 9343B is a novel, potent and selective inhibitor of calmodulin activity, which unlike other known calmodulin antagonists, does not inhibit protein kinase C activity and does not possess potential antidopaminergic activity. Here we show that CGS 9343B, like other calmodulin antagonists reported previously, is most effective in treatment of burns. 2. The effectiveness of CGS 9343B on skin burns was evaluated by electron microscopic studies, as well as by measurements of hemoglobin, ATP and enzymes which are markedly changed in the burned skin. 3. As CGS 9343B is a more selective probe for calmodulin function than other inhibitors, the similarity of its effects on burns to that of other calmodulin antagonists, strongly suggest that their action on burns is mediated through calmodulin inhibition.

Effects of chronic imipramine treatment on subclasses of platelet 3H-imipramine binding sites and plasma cortisol

A decreased density of platelet 3H-imipramine (3H-IMI) binding sites has been proposed as a putative trait marker of major depressive illness. However, subsequent studies have demonstrated that the number of such sites is increased so as to be more like normal controls upon chronic treatment with antidepressant drugs. In addition, there is some evidence to suggest that altered 3H-IMI binding may be secondary to elevated plasma cortisol levels which are common in depressed patients and which normalize with remission. The present study compares platelet 3H-imipramine binding, plasma cortisol levels, and clinical improvement of 10 endogenous depressed patients before and after 6 weeks of treatment with imipramine-HCl. Total high affinity 3H-IMI binding sites were further differentiated into two subclasses on the basis of their relative sensitivities to cyanoimipramine (CNIMI) inhibition. Treatment was associated with a significant increase (134%) in CNIMI resistant binding but a decrease (45.2%) in CNIMI sensitive binding. While the former was significantly correlated with posttreatment cortisol levels, no significant correlation was found between cortisol and CNIMI specific binding. Neither site appeared to be directly related to mood state. The significance of these findings to the evaluation of platelet binding as a trait dependent marker is discussed.

Characterization and inhibitor sensitivity of human sperm phospholipase A2: evidence against pivotal involvement of phospholipase A2 in the acrosome reaction

The kinetic properties and inhibitor sensitivity of human sperm phospholipase A2 (PLA2; EC 3.1.1.4) were studied. Phospholipase activity was isolated from human spermatozoa by acid extraction. Hydrolysis of dipalmitoyl phosphatidylcholine was specific to the sn-2 position. Activity was sensitive to product inhibition (60% inhibition by 0.1 mM lysophosphatidylcholine). The effects of Ca2+ and sodium deoxycholate on enzyme activity were biphasic; maximal activities were observed at 0.5 mM concentration of each agent. PLA2 was stimulated (135%) by 3% dimethylsulfoxide and was inhibited by elevated ionic strength (approximately 70% inhibition with either 0.2 M NaCl or 0.2 M KCl). Two molecular forms of PLA2 were kinetically distinguishable, one with an apparent Michaelis constant and maximal reaction velocity of 3.0 microM and 0.64 mlU/mg protein and the other with respective constants of 630 microM and 32.0 mlU/mg protein. Both forms of the enzyme were Ca2+ dependent and heat stable; however, the low-Km activity was less resistant to 60 degrees C preincubation at pH 7.5 (28% inactivation of low-Km activity after 45 min, as compared to no effect on high-Km activity). Quinacrine was a noncompetitive PLA2 inhibitor with Kis for low- and high-Km activities of 0.42 mM and 0.49 mM, respectively. Trifluoperazine (calmodulin antagonist) inhibited the high-Km activity noncompetitively (Ki = 87 microM) and the low-Km activity by a mechanism consistent with the removal of a nonessential activator. Dissociation and rate constants for inactivation of low- and high-Km activities by p-bromophenacyl bromide were 0.28 mM and 0.032 min-1, and 0.73 mM and 0.066 min-1, respectively. PLA2 was inhibited by p-nitrophenyl-p'-guanidinobenzoate, at higher concentrations (10(-4)-10(-3) M) than required to inhibit trypsinlike proteinases; p-aminobenzamidine, another potent trypsin/acrosin inhibitor, stimulated (approximately 40%) PLA2 at concentrations from 2-5 mM but inhibited PLA2 (40-50%) at a concentration of 10 mM. MnCl2 (5mM) inhibited low- and high-Km PLA2 activities by 77% and 76%, respectively. Quinacrine (0.4 mM), trifluoperazine (20 microM), p-bromophenacyl bromide (20 microM), and MnCl2 (5 mM) were tested as inhibitors of the ionophore A23187-induced human acrosome reaction. Inhibition was noted only with quinacrine (32%) and MnCl2 (93%). The effect of MnCl2 was restricted to an interaction with A23187, rather than with PLA2; p-Bromophenacyl bromide inhibited (P less than 0.05) PLA2 (29%) when added to intact spermatozoa but had no effect on the acrosome reaction. PLA2 inhibition was poorly correlated with the acrosome reaction.(ABSTRACT TRUNCATED AT 400 WORDS)

Forskolin stimulates prostaglandin synthesis in rabbit heart by a mechanism that requires calcium and is independent of cyclic AMP

Infusion of forskolin, an adenylate cyclase activator, in concentrations (2 microM) that do not alter basal prostaglandin (PG) synthesis inhibit synthesis of PG elicited by isoproterenol in rabbit heart. This inhibitory action of forskolin appears to be dependent on cyclic AMP (cAMP). Bolus injection of forskolin (75 nmol), however, was found to stimulate PG synthesis in rabbit heart. The purpose of this study was to elucidate the mechanism of the stimulatory action of forskolin on PG synthesis (prostaglandin I2 measured as 6-ketoprostaglandin F1 alpha [6-keto-PGF1 alpha]) in isolated perfused rabbit heart. Forskolin enhanced PG production in a dose-dependent manner. 1,9-Dideoxyforskolin, a forskolin analogue devoid of adenylate cyclase-stimulating activity, also enhanced PG synthesis. The cAMP analogue chlorophenylthio-cAMP failed to stimulate output of 6-keto-PGF1 alpha, although this agent produced dose-related changes in mechanical function in rabbit heart. Furthermore, the adenylate cyclase inhibitor (-)-N6-(R-phenylisopropyl)adenosine potentiated, whereas the phosphodiesterase inhibitor cilostamide attenuated, forskolin-stimulated PG production. (-)-N6-(R-Phenylisopropyl)adenosine and cilostamide had no effect on the mechanical actions of chlorophenylthio-cAMP, suggesting selectivity of these agents for adenylate cyclase and phosphodiesterase, respectively. 6-Keto-PGF1 alpha output elicited by forskolin was abolished by reduction of calcium in the perfusion fluid as well as by the calcium channel blocker diltiazem. The intracellular calcium antagonists TMB-8 and ryanodine also abolished forskolin-stimulated PG synthesis in rabbit heart. PG synthesis stimulated by 1,9-dideoxyforskolin was also prevented by reduced extracellular calcium, diltiazem, and ryanodine. The calmodulin antagonists trifluoperazine, W-7, and calmidazolium failed to significantly alter PG production in response to forskolin. These results indicate that forskolin-stimulated PG synthesis in rabbit heart is independent of cAMP and requires calcium from both extracellular and intracellular sources.

Ca2(+)-dependent synthesis of prostaglandin I2 and mobilization of arachidonic acid from phospholipids in cultured endothelial cells permeabilized with saponin

The feasibility of using saponin as a permeabilization agent to study the effect of free Ca2+ concentration ([Ca2+]f) on prostaglandin I2 (PGI2) synthesis and mobilization of arachidonic acid from membrane phospholipids was investigated in cultured bovine pulmonary artery endothelial cells (BPAEC). Treatment of BPAEC with 20 micrograms/ml saponin caused selective permeabilization of the plasma membrane as determined by measurements of the release of lactate dehydrogenase and beta-hexosaminidase. In cells prelabeled with [3H]arachidonic acid for 22 h, permeabilization with 20 micrograms/ml saponin induced PGI2 synthesis and release of [3H]arachidonic acid from membrane phospholipids. These effects were dependent upon [Ca2+]f in the range 72 nM to 5 microM. Release of [3H]arachidonic acid from phospholipid classes was determined in suspensions of BPAEC prelabeled with [3H]arachidonic acid and permeabilized with 20 micrograms/ml saponin. At [Ca2+]f optimal for PGI2 synthesis, 16.2% of the total incorporated [3H]arachidonic acid was released from phosphatidylinositol (3.4%), phosphatidylethanolamine (3.5%) and phosphatidylcholine (9.3%). The time course and dependence upon [Ca2+]f of [3H]arachidonic acid release from phospholipids correlated with PGI2 synthesis. The amount of PGI2 synthesized in permeabilized BPAEC was similar to that in cell cultures treated with the calcium ionophore A23187. In comparison, however, PGI2 synthesis induced by A23187 was associated with less release of [3H]arachidonic acid from membrane phospholipids, e.g., 2.3% versus 16.2%. The greater loss of [3H]arachidonic acid from phospholipids in saponin-permeabilized BPAEC was most likely due to the loss of cell integrity and/or nonspecific effects of the detergent on phospholipases. Despite these limitations, the Ca2+ dependence observed for PGI2 synthesis and [3H]arachidonic acid mobilization suggest that saponin-permeabilization may provide a useful system for studies of the intracellular events triggered by the rise in intracellular Ca2+ which culminate in PGI2 synthesis.

Phospholipase C from Clostridium perfringens stimulates phospholipase A2-mediated arachidonic acid release in cultured intestinal epithelial cells (INT 407)

The mechanisms by which phospholipase C from Clostridium perfringens stimulates release of arachidonic acid (AA) in cultured intestinal epithelial cells (INT-407) were investigated. INT-407 cells were first allowed to incorporate 14C-labeled AA into their phospholipids; the labeled cells were then exposed to phospholipase C, and the release of free 14C-AA was determined. Phospholipase C caused a rapid (3 min) intracellular rise of free 14C-AA, followed by a considerable, dose- and time-dependent release of 14C-AA into the extracellular medium. For comparison, the calcium ionophore A23187 also caused a rapid mobilization of free 14C-AA, but a much lower extracellular 14C-AA release than phospholipase C during longer (1 h) incubation. The 14C-AA release was accompanied by a degradation of 14C-myo-inositol-labeled phosphatidylinositols and was reduced by the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). Both phospholipase C- and A23187-stimulated 14C-AA release was associated with degradation of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol and was reduced by nordihydroguaiaretic acid and 4-bromophenacyl bromide, two known phospholipase A2 inhibitors. In addition, the 14C-AA release was reduced by the calmodulin inhibitors trifluoperazine, compound 48/80, and N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7). These findings indicate that phospholipase C from C. perfringens stimulates phospholipase A2-mediated AA release from human intestinal epithelial cells and suggest that this stimulation is brought about via processes involving phosphatidylinositol breakdown and activation of calmodulin and protein kinase C. It is possible that this phospholipase C-evoked AA release may contribute to the mucosal pathologic condition in diseases with altered intestinal microbial flora.

Characteristics of activation of rat mast cells by polyethylenimines and a polyallylamine: effects on the release of histamine and of arachidonate and its metabolites

1. Three polyethylenimines and one polyallylamine released radioactivity from rat peritoneal mast cells labeled with [1-14C]arachidonic acid and concomitantly released histamine from the cells. 2. This enhancement of the release of radioactivity was inhibited by phospholipase A2 inhibitors, quinacrine (1 mM) and p-bromophenacyl bromide (10 microM), suggesting that polyethylenimine and polyallylamine activates phospholipase A2 to generate arachidonate and its metabolites. 3. The effects of H-7 or K-252a, general kinase inhibitors for the release of histamine and of arachidonate and its metabolites induced by the polycations, were different from those of W-7, a calmodulin inhibitor. The mechanisms to generate arachidonate and its metabolites seemed to differ from those to release histamine; activation of phospholipase A2 by the polycations was calmodulin-dependent. 4. p-Bromophenacyl bromide inhibited the histamine release induced by polyethylenimines and a polyallylamine, suggesting that arachidonate production by means of phospholipase A2 activation by polycations is an important process in the release of histamine from mast cells.

Anti-ischemic and membrane stabilizing activity of calmodulin inhibitors

In the control perfused working rat hearts subjected to 25 min global ischemia, reperfusion resulted in a 50% recovery of the hemodynamic functions. A concentration-dependent improvement of this recovery and a reduction of the postischemic lactate dehydrogenase (LDH) release was caused by calmidazolium (CMZ), trifluoperazine (TFP), and chlorpromazine (CPZ) added prior to ischemia. The drugs were not effective when added only to the reperfusate. The concentrations of CMZ, TFP, and CPZ producing the half-maximal effects were 2.5 X 10(-9) M, 1.5 X 10(-7) M and 3 X 10(-7) M, respectively. Prolongation of the ischemic period caused a progressive deterioration of the functional recovery of the hearts while the total postischemic LDH release showed, at the same time, an initial gradual rise followed by a later decay. In untreated hearts the duration of ischemia resulting in 50% loss of hemodynamic function and in a maximal LDH release was 25 min. TFP (10(-6) M) and CMZ (10(-7) M) prolonged these times by 4-7 min and 5-10 min. respectively. TFP, CPZ, and CMZ protected the erythrocytes from osmotic hemolysis. The maximum anti-hemolytic activity was produced by 3 X 10(-6) M CMZ, 3 X 10(-5) M TFP, and 10(-4) CPZ. The concentration-dependency of this effect was not affected by low concentrations of sodium dodecyl sulphate (SDS). Neither TFP nor CMZ prevented the hemolysis produced by 10(-3) M SDS. It is concluded that the delay in the development of the ischemic injury produced by TFP and CMZ is due to the effects of these drugs as calmodulin antagonists rather than as membrane stabilizers.

Aggregation and/or oxygenated products of arachidonic acid are not required for collagen-induced deacylation of phosphatidylcholine in human platelets

In the present study the effects of collagen on platelet aggregation and arachidonic acid (AA) mobilization, specifically from phosphatidylcholine (PC), were investigated in the presence and absence of BW755C, a selective inhibitor of cyclo-oxygenase and lipoxygenases. The inhibition of cyclo-oxygenase and lipoxygenase(s) by BW755C (75 microM) resulted in severe impairment in collagen-induced platelet aggregation. In the presence of BW755C, the aggregation response amounted to 14, 26, 37 and 49% of the corresponding controls (without BW755C) at 10, 25, 50 and 100 micrograms of collagen respectively. On the contrary, the amount of AA released from PC, which ranged from 3.5 to 8.6 nmol/10(9) platelets, in response to the action of collagen (10-100 micrograms) remained unaffected by the presence of BW755C. Substantial amounts of non-esterified AA were detected in the free fatty acid fractions obtained from collagen-stimulated platelets in the presence as well as in the absence of BW755C. However, the presence of BW755C caused a greater accumulation of free AA (mass) and this ranged from 4 to 16 nmol, depending upon the amount of collagen. In addition, small increases in free stearic and oleic acids were observed in collagen-stimulated platelets as compared with unstimulated platelets. The amount of AA lost from PC represented 67, 80, 49 and 52% of the free AA obtained at 10, 25, 50 and 100 micrograms of collagen respectively. Our results adhesion of platelets to collagen fibres may be responsible for much of the AA release from PC Furthermore, these results demonstrate that aggregation and/or cyclo-oxygenase/lipoxygenase metabolites are not obligatory for the release of AA from PC in collagen-stimulated human platelets.

Changes in platelet 3H-imipramine binding with chronic imipramine treatment are not state-dependent

One month of imipramine treatment increased both the Kd and Bmax of platelet 3H-imipramine binding in 11 endogenous unipolar depressed patients. Continued treatment (13 weeks) of 5 patients subsequently lowered the Bmax values of 2 patients who had initially shown the largest increases, so that binding was no longer significantly elevated after 13 weeks. The observed changes in Kd but not in Bmax, could be explained by the carryover of tightly bound drug to the binding assay, although neither of the measures were correlated with plasma imipramine levels. Posttreatment Bmax (4 weeks) values were inversely related to plasma cortisol levels, although a weak but positive correlation was found before treatment. No significant change was found in plasma cortisol with treatment. Clinical responses were not related to cortisol or Bmax changes, although optimal improvement was associated with extreme values (high and low) of pretreatment Bmax. The present results, obtained with imipramine, and similar results obtained after nortriptyline and electroconvulsive shock by others, suggest that at least some antidepressants may induce transient changes in the Bmax of platelet binding that are independent of affective state.

Correlation of intracellular and extracellular calcium ion concentrations with synergy between 1,2-dioctanoyl-sn-glycerol and ionomycin in platelet arachidonic acid mobilization

The potentiation by 1,2-dioctanoyl-sn-glycerol (DiC8) of ionomycin-induced platelet production of 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) was investigated in correlation with extracellular Ca2+ concentrations and increases in [Ca2+]i, as detected with aequorin and fura-2. Extracellular Ca2+ concentrations greatly influenced the production of arachidonic acid metabolites induced by DiC8 and ionomycin, while that induced by ionomycin alone was minimally affected by variation of the extracellular Ca2+ concentration. In the synergy between ionomycin and 20 microM DiC8, the optimal concentrations of ionomycin shifted from high to low with increasing concentrations of extracellular Ca2+, suggesting that there might be a range of optimal [Ca2+]i for the production of the arachidonic acid metabolites. This hypothesis was confirmed by simultaneous measurements of [Ca2+]i increases, and the production of the arachidonic acid metabolites. With the aequorin method, the optimal concentrations of [Ca2+]i fell to between 10 microM and 20 microM, and with the fura-2 method, it fell to between 800 nM and 1800 nM. Direct measurements of [14C]arachidonic acid release suggested that the DiC8-potentiated production of arachidonic acid metabolites induced by ionomycin was attributable to increased arachidonic acid release. Since ionomycin and DiC8 induced relatively low levels of phosphatidic acid production, an indicator of phospholipase C activation, it was suggested that the increased arachidonic acid release was largely dependent upon phospholipase A2. Synergy between DiC8 and ionomycin was also observed with aggregation and serotonin release. Aggregation was induced by lower concentrations of ionomycin, and appeared to be more dependent upon extracellular Ca2+, while serotonin release required higher concentrations of ionomycin, and variations in extracellular Ca2+ affected the response minimally. These findings suggest that the mechanisms underlying the synergy between protein kinase C activation and Ca2+ mobilization differ among the three functions evaluated in this study.

Cyclosporin A inhibits prostaglandin E2 formation by rat mesangial cells in culture

A reversible reduction in glomerular filtration rate (GFR) is a frequent side effect in patients treated with the immunosuppressant cyclosporin A (CsA). The pathophysiology of acute CsA nephrotoxicity, however, is unclear. Since eicosanoids are local mediators of glomerular hemodynamics, they might be involved in CsA induced changes in GFR. We therefore studied the effect of CsA on prostaglandin E2 (PGE2) production by rat mesangial cells in culture. PGE2 production by mesangial cells following stimulation with angiotensin II (AII) (10(-6) M) or the Ca2+-ionophore A23187 (1 microgram/ml) was significantly inhibited when cells were grown for 24 hours in media which contained CsA (800 to 3200 ng/ml). CsA did not affect viability of mesangial cells as determined by 51Cr release or by cell proliferation measured by 3H-thymidine incorporation. CsA (3200 ng/ml) did not inhibit PGE2 formation by rat MC microsomes incubated with arachidonic acid. However, CsA, in a dose dependent manner, inhibited A23187 and angiotensin II induced release of 3H-labelled arachidonic acid from rat mesangial cells. These data demonstrate that CsA reduces PGE2 formation by rat mesangial cells in culture, probably by inhibiting the release of substrate arachidonic acid from cell membranes rather than by inhibition of cyclooxygenase. This effect may contribute to the reduction in GFR which accompanies CsA therapy.

H1-antihistamines and calmodulin antagonists inhibit the ionophore A23187-induced eicosanoid formation by human leukocytes

The effects of the H1-antihistamines astemizole, oxatomide and pyrilamine, of the calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), on the ionophore A23187 (5 mumol/l)-induced release of cysteinyl-leukotrienes (LT) and thromboxane (TX) B2 from mixed human leukocytes were investigated in comparison to those of the cyclooxygenase inhibitor indomethacin and the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA). In contrast to pyrilamine both astemizole and oxatomide inhibited the release of cysteinyl-LT and TXB2 with IC50 values between 4 and 23 mumol/l. Both astemizole and oxatomide were about twice as effective in inhibiting cysteinyl-LT release as compared to TXB2 release. Similar to astemizole and oxatomide the calmodulin antagonists trifluoperazine and W-7 inhibited the eicosanoid release. W-7 was, however, clearly less effective and in contrast to trifluoperazine no difference was observed in its potency to inhibit cysteinyl-LT or TXB2 release. The H1-antihistamines, astemizole and oxatomide as well as the calmodulin antagonists did not cause intracellular retention of the eicosanoids tested. The reference compounds indomethacin and NDGA proved to be the most potent inhibitors. The results demonstrate that the therapeutic antihistamines astemizole and oxatomide as well as the classical calmodulin antagonists trifluoperazine and W-7 are able to inhibit eicosanoid formation.

Treatment of frostbite with the calmodulin antagonists thioridazine and trifluoperazine

1. Thioridazine and trifluoperazine, which have been previously found in this laboratory to be the most effective calmodulin antagonists in treatment of burns, are shown here to be also effective in the treatment of frostbite. 2. Electron microscopic studies have revealed a complete reversal of both the vascular and skin tissue damage induced by frostbite. 3. The reversal of the vascular damage was also demonstrated by the ability of these compounds to abolish the increase in hemoglobin content in the skin. 4. The reversal of the skin tissue damage was also revealed by the ability of these compounds to raise the decreased ATP level and the reduced activities of 6-phosphogluconate dehydrogenase and mitochondrial and soluble hexokinase in skin, induced by frostbite, to normal control levels.

Therapeutic and prophylactic treatment of skin burns with several calmodulin antagonists

1. Several calmodulin antagonists abolished the decrease in ATP level and in the activities of 6-phosphogluconate dehydrogenase and mitochondrial and soluble hexokinase, induced by burns in the rat skin. 2. These antagonists had also a protective action on the blood capillaries and erythrocyte membrane, as judged by the electron microscopic appearance, as well as the abolishment of hemoglobin increase and burn edema. 3. Of all the compounds investigated here, the most effective were trifluoperazine and thioridazine, which are also known as the more potent calmodulin antagonists. 4. The present experiments suggest that calmodulin antagonists may be effective drugs in treatment of burns, having both therapeutic and prophylactic action.

Mobilization of arachidonic acid in collagen-stimulated human platelets

Stimulation of platelets with collagen results in the mobilization of arachidonic acid (AA) from phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). In this study the effect of aspirin, indomethacin, BW755C and prostaglandin H2 (PGH2) on labelled AA release in response to varied concentrations of collagen was investigated. Our results indicate that aspirin (0.56 mM) and indomethacin (5.6 microM) not only inhibited the collagen-mediated formation of cyclo-oxygenase metabolites, but also caused a significant reduction in the accumulation of free labelled AA and 12-hydroxyeicosatetraenoic acid (12-HETE) (21-64%). Aspirin and indomethacin also inhibited the release of [3H]AA from PC (37-75%) and PI (33-63%). The inhibition of AA release caused by aspirin was reversed partially by PGH2 (1 microM). In contrast, a smaller/no inhibition of collagen-stimulated labelled AA and 12-HETE accumulation (0-11%) and of collagen-stimulated AA loss from PC and PI was observed in the presence of BW755C. The results obtained in the presence of aspirin, indomethacin and BW755C at lower concentrations of collagen further demonstrate that AA release from PI (45-61% inhibition at 10 micrograms of collagen), but not from PC, was affected by the inhibition of cyclo-oxygenase. The results obtained on the effect of PGH2 further support that deacylation of phospholipids occurs independently of cyclo-oxygenase metabolites, particularly at higher concentrations of collagen. These results also demonstrate that aspirin and indomethacin, but not BW755C, cause a direct inhibition of collagen-induced [3H]AA liberation from PC as well as from PI. We also conclude that the diacylglycerol lipase pathway is a minor, but important, route for AA release from PI in collagen-stimulated human platelets. The mechanisms underlying the regulation of AA release by collagen in the absence of cyclo-oxygenase metabolites are not clear.

The effect of hyperbaric oxygenation and hypoxia on the blood-nerve barrier

We measured the permeability coefficient--surface area product (PA) of peripheral nerve to [14C]sucrose in rat sciatic nerve in experimental chronic hypoxic hypoxia of up to 8 weeks and following hyperbaric oxygenation for 1 to 4 weeks. Chronic hypoxia caused an increase in PA presumably indicating impairment of the blood-nerve barrier at 4 weeks with restoration to normal by 8 weeks. Hyperbaric oxygenation (100% oxygen at 2.5 ata for 120 min/day 5 days per week) caused a mild but time dependent increase in PA reaching statistical significance by 4 weeks.