Calmodulin stimulates human platelet phospholipase A2

Selective inhibition of free arachidonic acid production in activated alveolar macrophages by calmodulin antagonists

The effect of calmodulin antagonists on the amounts of free fatty acids produced by rabbit alveolar macrophages was determined by fluorometric high-performance liquid chromatography. Opsonized zymosan-induced arachidonic acid production was dramatically suppressed in the presence of W-7 and trifluoperazine without an effect on the production of other fatty acids. Calmodulin antagonists inhibited phospholipase A and abolished the release of arachidonic acid from phospholipids. The present results suggest that a zymosan-sensitive pool of 20:4, which is different from that of other fatty acids, is present in macrophages and that calmodulin antagonists selectively inhibit phospholipase A, which preferentially degrades phospholipids with 20:4.

An extracellular role for calmodulin-like activity in cell proliferation

1. Addition of extracellular pure pig brain calmodulin was found to modulate DNA synthesis and cell proliferation in K562 human leukaemic lymphocytes. At lower cell densities calmodulin significantly stimulated [3H]thymidine uptake; at higher densities it decreased it. 2. A protein biochemically indistinguishable from calmodulin was detected in the cell-conditioned media of rapidly dividing K562 cells. The concentration of calmodulin-like activity found in the conditioned media of these and a range of other normal and neoplastic cells (250-1636 ng/ml) was of the same order as would stimulate DNA synthesis in subconfluent cells. 3. Amounts of extracellular calmodulin-like activity and immunoreactivity varied during cell growth from low to high density, a peak of extracellular calmodulin preceding DNA synthesis in synchronized K562 cells. Extracellular calmodulin concentrations did not correlate with the presence of lactate dehydrogenase in the medium. 4. Inhibition of extracellular calmodulin activity by calmodulin antagonist immobilized on agarose beads, or by antibody to calmodulin, significantly decreased DNA synthesis. 5. These data strongly suggest that calmodulin or a very closely related protein can influence mitosis through an extracellular mechanism.

Neurohormonal regulation of calcium in the cell

Neurohormone C (NC) is a glycopeptide isolated from bovine hypothalamus, which inhibits Ca-calmodulin (CaM)-dependent cAMP and cGMP phosphodiesterase (PDE) and is a regulator of Ca in the cell. Distribution of [45Ca]CaCl2 in the mitochondria and reticulum (SR) of heart and brain mitochondria and changes of Ca-binding proteins in these organelles under NC influence have been studied in the myocardium before and after isoproterenol-induced necrosis. Intraperitoneal administration of 80-100 mU of PDE inhibitory activity of NC to rats did not cause any noticeable changes in the protein content of intracellular organelles, but altered the affinity of certain proteins to 45Ca2+. This property of NC was especially noticeable after isoproterenol necrosis. Necrotic injury of the myocardium induced Ca2+ storage in the mitochondria and SR of brain, and decreased the Ca2+ concentration in myocardial mitochondria. NC injection to the animals with necrosis was followed by Ca2+ release from all the studied organelles.

Arachidonic acid metabolism in Ascidia ceratodes eggs: role of lipid peroxidation

1. Addition of arachidonic acid (AA) to Ascidia ceratodes oocyte homogenates results in its rapid oxidation to several polar products. 2. AA oxidation in homogenates has both calcium independent and calcium stimulated components. 3. Calcium or AA addition to an oocyte homogenate stimulates O2-consumption. 4. Stimulation of homogenate O2-consumption by AA and calcium is additive. 5. Intact eggs oxidize AA to products similar to those detected in vitro. 6. Quantitatively total AA oxidation was similar for unfertilized and fertilizing eggs and dividing embryos, while qualitative differences were detected for the three stages. 7. These results demonstrate the presence of lipoxygenase-like, peroxidizing activity, in Ascidia eggs that is capable of producing products potentially important to the control of early metabolic events during development.

Inhibitors of inositol trisphosphate-induced Ca2+ release from isolated platelet membrane vesicles

Platelet membrane vesicles accumulated Ca2+ in an ATP-dependent fashion, and 25-50% of the accumulated Ca2+ was released by the addition of 10 microM inositol 1,4,5-trisphosphate (IP3). The concentration of IP3 required for half-maximal Ca2+ release was approximately 0.5 microM. The inhibition of IP3-induced Ca2+ release from these membrane vesicles by various agents was examined. Of the plasma membrane Ca2+ channel blockers, cinnarizine and flunarizine were found to be potent inhibitors of IP3-induced Ca2+ release while having no effect on ATP-dependent Ca2+ uptake. The IC50 value for both cinnarizine and flunarizine as inhibitors of IP3-induced Ca2+ release was below 10(-6) M. Nifedipine, verapamil, bepridil, and diltiazem did not significantly inhibit IP3-induced Ca2+ release at the highest concentration tested (50 microM). The "intracellular Ca2+ antagonists" ryanodine, TMB-8 (8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate), dantroline, trifluoperazine and chlorpromazine were not inhibitors of IP3-induced Ca2+ release at 50 microM. The local anesthetics benzocaine and lidocaine weakly inhibited the IP3-induced Ca2+ release with IC50 values of approximately 5 and 50 microM, respectively, whereas other local anesthetics tested were less potent inhibitors. The potent inhibitors described may prove useful as probes of the IP3-induced Ca2+ release channels.

Role of prostaglandins and leukotrienes in volume regulation by Ehrlich ascites tumor cells

PGE2 and LTC4 syntheses in Ehrlich ascites cells were measured by radioimmunoassay. Hypotonic swelling results in stimulation of the leukotriene synthesis and a concomitant reduction in the prostaglandin synthesis. If the cells have access to sufficient arachidonic acid there is a parallel increase in the synthesis of both leukotrienes and prostaglandins following hypotonic exposure. PGE2 significantly inhibits regulatory volume decrease (RVD) following hypotonic swelling in Na-containing medium but not in Na-free media, supporting the hypothesis that the effect of PGE2 is on the Na permeability. PGE2 also had no effect on RVD in Na-free media in the presence of the cation ionophore gramicidin. Since the Cl permeability becomes rate limiting for RVD in the presence of gramicidin, whereas the K permeability is rate limiting in its absence, it is concluded that PGE2 neither affects Cl nor K permeability. Addition of LTD4 accelerates RVD and since the K permeability is rate limiting for RVD this shows that LTD4 stimulates the K permeability. Inhibition of the leukotriene synthesis by nordihydroguaiaretic acid inhibits RVD even when a high K conductance has been ensured by the presence of gramicidin. It is, therefore, proposed that an increase in leukotriene synthesis after hypotonic swelling is involved also in the activation of the Cl transport pathway.

Cyclosporin A inhibits PGE2 release from vascular smooth muscle cells

The influence of the fungoid undecapeptide cyclosporin A (CyA) on PGE2 release from cultured rat aortic smooth muscle cells was investigated in this study. We found that CyA time and concentration dependently (ED50:500 ng/ml) inhibited PGE2 release from the cells. CyA attenuated both basal and PGE2 release evoked by angiotensin II (10(-10)-10(-6) M), arginine vasopressin (10(-10)-10(-6) M) and ionomycin (10(-9)-10(-6) M). CyA (1 microgram/ml) did not affect the conversion of exogenous arachidonic acid (1 microM) into PGE2. The inhibitory effect of CyA was neutralized by high concentrations of the calcium ionophore ionomycin (greater than 3 X 10(-6) M). Taken together our results indicate that CyA inhibits both basal and vasoconstrictor evoked PGE2 release from vascular smooth muscle by impairing the availability of free arachidonic acid rather than by inhibiting the conversion of arachidonic acid into PGE2.

Effects of calmodulin inhibitors on rabbit synoviocyte phospholipase A2

The effect of calmodulin inhibitors on synoviocyte phospholipase A2 activity was evaluated. Cells were incubated with [3H]arachidonic acid after 24 hours to label phospholipids. [3H]prostaglandin E2 synthesis was stimulated by Salmonella minnesota lipopolysaccharide (100 micrograms/ml). Trifluoperazine, 35 microM, reduced lipopolysaccharide-stimulated [3H]prostaglandin E2 synthesis by 50%. In sonicated suspensions of cells, calcium-dependent phospholipase A2 activity was inhibited by trifluoperazine 3-100 microM and by compound 48/80 (3 micrograms/ml). These agents inhibit calmodulin-dependent enzyme activity. The addition of calmodulin, 1 or 2.5 microM, to compound 48/80-treated suspensions reversed this inhibition in a dose-dependent manner. Agents which inhibit calmodulin-dependent enzymes can reversibly inhibit synoviocyte phospholipase A2 and thus prostaglandin E2 production.

Compound 48/80 is a potent inhibitor of phospholipase C and a dual modulator of phospholipase A2 from human platelet

Compound 48/80 inhibited phosphatidylinositol-specific phospholipase C activity from human platelets. Whereas 1 microgram/ml of compound 48/80 slightly stimulated Ca2+-dependent phospholipase A2, higher concentrations led to dose-dependent inhibition of this platelet enzyme. This biphasic effect was confirmed with phospholipases A2 purified from rat liver and human synovial fluid. The aggregation of human platelets induced by ADP and PAF-acether was inhibited by compound 48/80, whereas the aggregation induced by ionophore A23187 was not modified by this compound. These results demonstrate that the inhibition of platelet aggregation by compound 48/80 is not due solely to effects on calmodulin as previously reported, but that inhibition of phospholipases and probably arachidonate mobilization may also be involved.

Mechanism of complement-mediated thromboxane production by the perfused rabbit liver: lack of effect of dantrolene sodium

Activated components of the complement system have been shown to stimulate the arachidonic acid cascade. We have reported that hepatic thromboxane production in response to plasma activated with zymosan is self-limiting, not affected by nifedipine, but inhibited by mepacrine, a phospholipase inhibitor. To further study this relationship, we have tested the effects of dantrolene sodium, an agent reported to immobilize intracellular calcium. Control group livers were perfused with Krebs-Henseleit bicarbonate buffer at a rate of 120 ml/min in a nonrecirculating perfusion system and administered 1 ml/min of normal rabbit plasma for 10 minutes. This group of livers demonstrated stable wet weight, perfusion pressure, and rates of release of lactic dehydrogenase, thromboxane B2, and prostacyclin over a 150 minute experimental period. In contrast, the administration of 1 ml/min of zymosan-activated plasma resulted in significant increases in the rate of thromboxane B2 release at 1, 3, and 5 minutes after the start of the infusion. The rate of thromboxane production then returned to baseline values. Neither prostacyclin nor lactic dehydrogenase release changed significantly after ZAP. A similar change in thromboxane production following ZAP administration was seen in livers being continually perfused with 10 microM dantrolene sodium. Perfusion pressure was significantly elevated in this group during the ZAP infusion period. These results confirm complement-mediated thromboxane production in the isolated rabbit liver model but do not describe a definitive role of dantrolene-sensitive intracellular calcium release in the mechanism of ZAP-mediated thromboxane production.

Effects of calcium and parathyroid hormone on prostacyclin synthesis by vascular tissue

Prostacyclin generation by rat aortic rings was studied at different calcium concentrations. Extracellular calcium influenced prostacyclin synthesis, as reflected by the release of 6-keto-PGF1 alpha into the medium, in a concentration-dependent fashion. Calcium levels beyond the physiological range (1.12-1.25 mM unbound calcium) markedly stimulated 6-keto-PGF1 alpha production when compared with calcium-free solutions. On the other hand, addition of purified parathyroid hormone did not change 6-keto-PGF1 alpha production at any calcium concentration tested. These data suggest that parathyroid hormone has no direct effect on prostacyclin synthesis by vascular tissue, although it might influence prostacyclin generation through changes in extracellular calcium levels.

Stimulation of arachidonic acid metabolism via phospholipase A2 by triethyl lead

Human blood platelet aggregation and the formation of icosanoids were studied in response to triethyl lead chloride (Et3PbCl). Concentrations higher than 75 microM stimulate platelets to aggregate, whereas low concentrations (less than or equal to 20 microM) caused platelet hypersensitivity to aggregating agents such as collagen or arachidonic acid. Incubation of suspensions of washed platelets with Et3PbCl resulted in a stimulated liberation and subsequent metabolism of arachidonic acid. This response was dependent on the concentration of Et3PbCl and the incubation time. Using low concentrations of Et3PbCl and up to 3 h of incubation, the lipoxygenase product 12-hydroxy-5,8,10,14-icosatetraenoic acid was the major metabolite. Under normal conditions, however, stimulation of platelets with collagen, thrombin, or arachidonic acid leads to higher amounts of the cyclooxygenase products 12-hydroxy-5,8,10-heptadecatrienoic acid and thromboxane B2. The aggregation of human platelets induced by Et3PbCl was inhibited by three different drugs: acetylsalicylic acid, forskolin and quinacrine; but only quinacrine could prevent the liberation of arachidonic acid and the appearance of its metabolites. These specific effects of the inhibitors on Et3PbCl-stimulated platelets as well as the differences in the pattern of arachidonic acid metabolites and phosphatidic acid suggest a direct stimulatory action of Et3PbCl on platelet phospholipase A2.

Mechanism of vasopressin-induced platelet aggregation

The mechanism of aggregation induced by arginine vasopressin (AVP) was studied in human platelet rich plasma. AVP--over the range of 1.8-113.6 mU/ml--caused a dose-dependent aggregation with a concomitant stimulation of thromboxane B2 (TXB2) formation. d(CH2)5Tyr (Me)AVP did not by itself affect platelet aggregation or TXB2 release, but completely inhibited the action of AVP. DDAVP up to the concentration of 280 pM/ml had no effect on aggregation. Pretreatment of platelets with verapamil, trifluoroperazine or methylimidazole, a thromboxane synthetase blocker, prevented AVP-induced aggregation and TXB2 release. Neither phenidone in lower concentration nor nordihydroguaiaretic acid inhibited the ability of AVP to induce aggregation and TXB2 release. These results are consistent with the hypothesis that human platelets possess AVP receptor of the calcium-dependent vasopressor (V1) subtype and suggest that AVP-induced platelet aggregation is mediated via thromboxane release.

Solubilization and properties of Ca2+-dependent human platelet phospholipase A2

Using a sonicated dispersion of radiolabeled 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine as substrate, we found that phospholipase A2 activity of human platelets was enhanced 2.4-fold by albumin (1 mg/ml). The enzyme was recovered predominantly in the cytosolic fraction of platelets with less than a third of its activity being associated with the membrane fraction. In the presence of 24 mM n-octyl-beta-D-glucopyranoside (octylglucoside) phospholipase A2 was effectively (more than 90%) extracted from platelet lysates without solubilization of platelet membranes. Ion exchange chromatography of the soluble enzyme yielded a phospholipase A2 of unchanged total activity and great stability. This phospholipase A2 was active only in the presence of divalent cations (Ca2+ greater than Sr2+ greater than Mg2+ = 0), required albumin for optimal activity and exhibited exclusive positional specificity for the acyl ester bond at the 2-position of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine. Indomethacin (500 microM), mepacrine (500 microM) and N-ethylmaleimide (4 mM) inhibited the phospholipase A2 by 69, 62 and 19%, respectively. The results are discussed in the light of previous findings on human platelet phospholipase A2.

Possible role of calmodulin in the control of histamine release from human basophil leukocytes

We investigated the possible role of calmodulin (CaM) in the control of histamine release from human basophil leukocytes using several CaM antagonists. Trifluoperazine (TFP) (10(-6)-2 X 10(-5) M), pimozide (10(-6)-1.5 X 10(-5) M), chlorpromazine (CPZ) (10(-5)-10(-4) M) and promethazine (PMZ) (2 X 10(-5)-10(-4) M) inhibited in vitro histamine secretion from human basophils induced by several immunological (antigen, anti-IgE, and formyl-L-methionyl-L-leucyl-L-phenylalanine: f-met peptide) and nonimmunological (Ca2+ ionophore A23187 and the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate: TPA) stimuli. Trifluoperazine sulfoxide (TFP-S) and chlorpromazine sulfoxide (CPZ-S), which have very low affinity to CaM, had practically no inhibitory effect on histamine release from human basophils. The inhibitory effect of TFP could be made irreversible by irradiating the cells with UV light. A sulfonamide derivative, the compound N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7) (2.5 X 10(-5)-2 X 10(-4) M), which selectively binds to CaM, inhibited the release of histamine from basophils. In contrast, the chloride deficient analogue, W-5, which interacts only weakly with CaM, had practically no inhibiting effect. The IC50 for enzyme release by a series of eight CaM antagonists was closely correlated (r = 0.91; p less than 0.001) with the CaM specific binding, supporting the concept that these agents act by binding to CaM and thereby inhibiting histamine release. TFP and W-7 inhibited histamine release in the absence and in the presence of increasing concentrations of extracellular Ca2+. These results emphasize the possible role of CaM in the control of histamine secretion from human basophils.

Relationship between cellular calcium and prostaglandin synthesis in cultured vascular smooth muscle cells

We have investigated the effects of extracellular and intracellular Ca deficits and of pharmacologic agents thought to inhibit Ca influx or intracellular Ca mobilization on vasopressin-evoked changes of cytosolic Ca2+ levels and PG synthesis in cultured rat mesenteric arterial vascular smooth muscle cells. Vasopressin rapidly increased cytosolic Ca2+ as well as PG synthesis. The increase of cytosolic Ca2+ and the rate of PG synthesis were both maximal within the first minute of incubation. An extracellular Ca deficit of short duration partially inhibited both vasopressin-evoked PG synthesis and the increase of cytosolic Ca2+ by 40 to 60%. Two procedures which deplete cells of some of their intracellular Ca, namely a 30 min incubation in EGTA-supplemented, Ca-lacking media, or a 1 min incubation with ionophore A23187 in Ca-deficient media, decreased PG synthesis by 65% to 100%. The addition of extracellular Ca to Ca-depleted cells restored the ability of vasopressin to stimulate PG synthesis. Two Ca channel antagonists, nifedipine or cinnarizine, had no effect on either vasopressin-evoked PG synthesis or increased cytosolic Ca2+, whereas TMB-8 (10 microM), a putative inhibitor of intracellular Ca mobilization, decreased PG synthesis by 75% by inhibiting acylhydrolase as well as cyclo-oxygenase activities, but had no effect on basal or vasopressin-evoked increase of cytosolic Ca2+, documenting that its inhibitory effect was not a consequence of decreased cytosolic Ca2+. These results demonstrate that decreased cellular Ca levels are associated with decreased cytosolic Ca2+ levels and PG synthesis, and support the hypothesis of a link between, on the one hand, cellular Ca and/or cytosolic Ca2+ and on the other hand, PG synthesis.

Effect of calmodulin antagonists on hypoxia and reoxygenation damage in isolated rabbit hearts

The effect of calmodulin antagonists trifluoperazine (2.5 X 10(-7) M and 2.5 X 10(-6) M) and R 24571 (10(-8) M and 10(-7) M) on Langendorff-perfused rabbit hearts subjected to 180 min hypoxia and 30 min reoxygenation was studied. Coronary flow, force of contraction, oxygen consumption and release of lactate, noradrenaline and LDH were measured. Both drugs were found to reduce some of the deleterious consequences of hypoxia, i.e., they caused: marked reduction in the hypoxic LDH release; reduction in hypoxic contracture; increased recovery of active tension, oxygen consumption and coronary flow upon reoxygenation as compared to those in the untreated controls. The drugs prevented reoxygenation-induced LDH release in the drug-pretreated hearts and had no effect when given only during reoxygenation. This suggests that the drugs do not prevent reoxygenation damage as such, but only some changes developing during hypoxia, which make myocardium vulnerable to the reoxygenation damage. Although other interpretations are possible (e.g., the effects are related to the membrane stabilizing action of the drugs), our data are consistent with the hypothesis that a calmodulin-sensitive process is involved in the hypoxia damage of the myocardium.

Liberation of [3H]arachidonic acid and changes in cytosolic free calcium in fura-2-loaded human platelets stimulated by ionomycin and collagen

Cytosolic Ca2+ levels and arachidonate liberation were investigated in platelets loaded with the fluorescent Ca2+ indicator dye fura-2, and labelled with [3H]arachidonate. Fura-2 was used in preference to quin2 because the latter interfered with [3H]arachidonate labelling of phospholipids. From a resting free Ca2+ level of around 100 nM, ionomycin (10-200 nM) evoked an instantaneous, concentration-dependent increase in cytosolic Ca2+ that only resulted in [3H]arachidonate liberation (up to 4-fold over control) at Ca2+ levels greater than 1 microM. Addition of collagen (10 micrograms/ml) evoked an elevation in Ca2+ up to 461 +/- 133 nM. These changes in Ca2+ were accompanied by a 2-4-fold elevation in [3H]arachidonate with depletion of [3H]phosphatidylcholine by 17 +/- 4% and [3H]phosphatidylinositol by 41 +/- 7%. Indomethacin (10 microM) reduced the elevation in Ca2+ by collagen to 115 +/- 18 nM but did not significantly inhibit the 2-4-fold increase in [3H]arachidonate. [3H]Phosphatidylcholine and [3H]phosphatidylinositol were decreased by 9 +/- 7% and 10 +/- 6%, respectively, with collagen in the presence of indomethacin. Stimulation of phosphoinositide turnover by collagen in the presence and absence of indomethacin was indicated by [32P]phosphatidate formation in cells prelabelled with [32P]Pi. This phosphatidate formation was decreased (75%) by the presence of indomethacin. In the presence of indomethacin, phorbol myristate acetate (20 nM) alone or in combination with ionomycin (30 nM) failed to stimulate arachidonate liberation despite a marked stimulation of aggregation. These results indicate that, whereas ionomycin requires Ca2+ in the microM range for arachidonate liberation, collagen, notably in the presence of indomethacin, does so at basal Ca2+ levels. The mechanisms underlying the regulation of arachidonate release by collagen are not clear, but do not appear to involve activation of protein kinase C, or an elevation of cytosolic free Ca2+.

Calmodulin-independent inhibition of platelet phospholipase A2 by calmodulin antagonists

We tested the effects of calmodulin, two types of calmodulin antagonists, and various phospholipids on the phospholipase A2 activities of intact platelets, platelet membranes, and partially purified enzyme preparations. Trifluoperazine, chlorpromazine (phenothiazines) and N-(6-amino-hexyl)-5-chloro-1-naphthalenesulfonamide (W-7), at concentrations which antagonize the effects of calmodulin, significantly inhibited thrombin- and Ca2+ ionophore-induced production of arachidonic acid metabolites by suspensions of rabbit platelets and Ca2+-induced arachidonic acid release from phospholipids of membrane fractions, but not phospholipase A2 activity in purified enzyme preparations. The addition of acidic phospholipids, but not calmodulin, stimulated phospholipase A2 activity in purified enzyme preparations while decreasing its Km for Ca2+. The dose-response and kinetics of inhibition by calmodulin antagonists of acidic phospholipid-activated phospholipase A2 activity in purified preparations were similar to those of Ca2+-induced arachidonic acid release from membrane fractions. Calmodulin antagonists were also found to inhibit Ca2+ binding to acidic phospholipids in a similar dose-dependent manner. Our results suggest that the platelet phospholipase A2 is the key enzyme involved in arachidonic acid mobilization in platelets and is regulated by acidic phospholipids in a Ca2+-dependent manner and that calmodulin antagonists inhibit phospholipase A2 activity via an action on acidic phospholipids.

Inhibition of endothelium-dependent smooth muscle relaxation by calmodulin antagonists

By using the calmodulin antagonists, calmidazolium and N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7), the hypothesis was investigated as to whether calmodulin is involved in the sequence of events leading to the endothelium-dependent vascular smooth muscle relaxation. Endothelium-dependent relaxations were studied on two different preparations, the rabbit aorta and the pulmonary artery of the guinea pig. Relaxations were produced in the precontracted rings (noradrenaline 3 X 10(-6) mol/l) in response to acetylcholine, 10(-8) to 10(-6) mol/l (aorta), histamine, 3 X 10(-8) to 1 X 10(-6) mol/l (pulmonary artery) or the calcium ionophore A 23187, 1 X 10(-8) to 3 X 10(-7) mol/l (aorta and pulmonary artery). In the presence of calmidazolium and W-7 the endothelium-dependent relaxation was inhibited in a dose dependent manner. This inhibition was seen in a concentration range that coincides with calmodulin inhibition. The half maximal concentrations of calmidazolium for the inhibition of the relaxation of the aorta induced by acetylcholine and A 23187 were 3 X 10(-6) mol/l and 1.4 X 10(-6) mol/l and that of W-7 were 3.1 X 10(-5) and 3.6 X 10(-5) mol/l, respectively. Complete inhibition was obtained both for acetylcholine-and for A 23187-induced relaxations by preincubation with 1 X 10(-5) mol/l calmidazolium or 1 X 10(-4) mol/l W-7. The half maximal concentrations of calmidazolium for the inhibition of the relaxation of the pulmonary artery in response to histamine and A 23187 were 2.7 X 10(-6) mol/l and 3 X 10(-6) mol/l and complete inhibition was achieved at 1 X 10(-5) mol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Trifluoperazine and W-7 inhibit mating in Chlamydomonas at an early stage of gametic interaction

Gametic mating by Chlamydomonas reinhardi is inhibited in a dose-dependent and reversible manner by the calmodulin antagonists trifluoperazine (TFP) and W-7, but not by W-5, an analog of W-7 having lower affinity for calmodulin. Quantitation of the sequential steps of mating showed that TFP and W-7 both allow normal levels of flagellar agglutination but prevent all subsequent steps. Gametes agglutinate aberrantly and do not form mating pairs. Further, both of these drugs prevent the translocation of latex beads along the flagellar surface. Our observations suggest that calmodulin may play an integral role in the translocation of flagellar adhesion sites during the tip-locking stage of the Chlamydomonas mating reaction. Flagellar surface motility may be crucial to the transduction of signals during mating and may share regulatory mechanisms with other forms of surface motility.

Contamination of commercial preparations of calmodulin by phospholipase A2

In the course of studies of the possible regulation of cellular phospholipase A2 activities by calcium and calmodulin, it was observed that some of the commercial preparations of calmodulin contained significant phospholipase A2 activity. Six commercially available calmodulin sources were compared for the presence of contaminating phospholipase A2 activity, relative purity by SDS-gel electrophoresis, and relative biological activity in stimulating calmodulin-deficient phosphodiesterase. One of the commercial calmodulin sources contained a relatively high specific phospholipase A2 activity (1.30 +/- 0.11 nmol [1-14C]arachidonic acid released/mg protein per h) and yielded two major bands in SDS-gel electrophoresis. Two of the calmodulin sources tested were relatively free of phospholipase A2 activity, were quite pure (one band on SDS-gel) and had high biological activity in stimulating calmodulin-deficient phosphodiesterase. Thus, investigators using commercially available preparations of calmodulin should be aware of the contamination of some of these sources by phospholipase A2 activity. These findings may be of importance to investigators considering the role of calmodulin in activating a variety of calcium-dependent enzymes, including phospholipase A2.

Ca2+ homeostasis and cytotoxicity in isolated hepatocytes: studies with extracellular adenosine 5'-triphosphate

The incubation of isolated rat hepatocytes with extracellular adenosine 5'-triphosphate (ATP) resulted in an inhibition of Ca2+ efflux. The ATP-induced Ca2+ accumulation as determined by the increase in phosphorylase a activity and the Ca2+-sensitive fluorescent indicator (2-[(2-bis-[carboxymethyl]-amino-5-methylphenoxy)-methyl]-6-methoxy-8- bis-[carboxymethyl]aminoquinoline-tetrakis-[acetoxymethyl]ester) (Quin 2-AM) was associated with both the hydrolysis of ATP and the phosphorylation of a 110 kDa protein. No significant alteration in the intracellular ATP level was observed. The appearance of surface blebs and cytotoxicity followed the rise in cytosolic Ca2+, suggesting that the increased free Ca2+ may be responsible for the loss of viability. When a calmodulin inhibitor, 1-[bis(4-chlorophenyl)methyl]-3-[ 2-(2,4-dichlorophenyl)-2-[(2,4-dichlorophenyl)methoxy] ethyl]-1H- imidazolium chloride (calmidazolium), was included in the medium prior to ATP addition, bleb formation was reduced and the loss of viability was completely prevented, indicating that a Ca2+-calmodulin process may be involved in the initiation of cytotoxicity.

Some aspects of rat platelet and serum phospholipase A2 activities

Rat platelet lysate contained appreciable phospholipase A2 activity. In agreement with literature data this enzymatic activity eluted in the void volume of a Sephadex G-100 column. When the void volume peak was chromatographed over a Matrex gel blue A column, part of the phospholipase A2 activity ran through, whereas the remainder was bound to the gel. The latter activity could be eluted with buffers containing a high salt concentration. In contrast, phospholipase A2 activity solubilized from rat platelet lysates by treatment with high salt eluted from Sephadex G-100 columns with an apparent molecular weight of 10-15 kDa. This solubilized enzyme completely bound to Matrex gel blue A and, in the presence of Ca2+ also to an alkylphosphocholine-AH Sepharose affinity column. No indications were obtained for the presence of inactive phospholipase A2 and activator proteins in rat platelet lysates as described by Etienne, J., Grüber, A. and Polonovski, J. ((1980) Biochim. Biophys. Acta 619, 693-698; (1982) Biochemie 64, 377-380). Phospholipase A2 activity, both the associated form in platelet lysate and the monomeric form as eluted from Sephadex G-100 was slightly inhibited by trifluoperazine but calmodulin exerted no stimulation. Likewise, phospholipase A2 activity from rat serum eluted in the void volume of a Sephadex G-100 column. Rather than indicating the presence of high molecular weight forms of the enzyme, this is apparently caused by association with lipids or other proteins, in that chromatography in the presence of high salt revealed a molecular weight similar to that found for solubilized platelet phospholipase A2 activity.

Inhibition of phospholipase A2 by tiaramide in rabbit platelets

The mechanism by which tiaramide inhibited platelet aggregation was investigated using phospholipid labelling techniques by 14C-arachidonic acid (AA) and thin-layer chromatography. Tiaramide did not affect cyclo-oxygenase nor thromboxane synthetase, because TXB2 was detected in tiaramide-treated platelets, unlike aspirin-treated ones, and PGE2 and PGD2 did not increase, unlike in platelets treated with OKY-1581 (an inhibitor of thromboxane synthetase). Total phospholipid radioactivity was 82.5% of radioactivity recovered before aggregation, and this decreased to 49.0% (n = 5, P less than 0.05) after aggregation by collagen (30 micrograms/ml). AA radioactivity was 9.6% before aggregation and 40.0% after. Tiaramide (100 microM) restored total phospholipid and AA levels to those before aggregation. Tiaramide decreased the amount of AA liberated from 2-(3H-arachidonyl)phosphatidylcholine by whole platelet phospholipase A2 (PLA2). Tiaramide at 10 microM inhibited collagen-induced aggregation, but not that by AA. Tiaramide did not affect 45Ca-uptake by itself nor collagen-induced 45Ca-uptake from the external medium. Tiaramide did not inhibit intracellular Ca mobilization, and it did not affect the calmodulin-dependent cyclic nucleotide phosphodiesterase of rabbit brain. These facts suggest that tiaramide inhibits platelet PLA2 through mechanisms other than the blockade of Ca-influx and intracellular Ca mobilization or antagonism to calmodulin.

Evidence that the platelet plasma membrane does not contain a (Ca2+ + Mg2+)-dependent ATPase

The present study was designed to determine the subcellular distribution of the platelet (Ca2+ + Mg2+)-ATPase. Human platelets were surface labeled by the periodate-boro[3H]hydride method. Plasma membrane vesicles were then isolated to a purity of approx. 90% by a procedure utilizing wheat germ agglutinin affinity chromatography. These membranes were found to be 2.6-fold enriched in surface glycoproteins compared to an unfractionated vesicle fraction and almost 7-fold enriched compared to intact platelets. In contrast, the isolated plasma membranes showed a decreased specific activity of the (Ca2+ + Mg2+)-ATPase compared to the unfractionated vesicle fraction. This decrease in specific activity was found to be similar to that of an endoplasmic reticulum marker, glucose-6-phosphatase, and to that of a platelet inner membrane marker, phospholipase A2. We conclude, therefore, that the (Ca2+ + Mg2+)-ATPase is not located in the platelet plasma membrane but is restricted to membranes of intracellular origin.

Calcium-dependent binding of calmodulin to phospholipase A2 subunits induces enzymatic activation

Calmodulin interacted with phospholipase A2 from two different sources, as established by affinity chromatography, dimethylsuberimidate protein crosslinking, and phospholipase A2 assays. Calmodulin was covalently crosslinked to pancreatic and bee venom phospholipases A2 in a calcium-dependent manner, and enhanced the enzymatic activities of these phospholipases. Pancreatic phospholipase A2 was separated into two species of identical molecular weight by calmodulin affinity chromatography; the species that bound to immobilized calmodulin in a calcium-dependent manner was stimulated by calmodulin. This presents further evidence that phospholipase A2 is directly activated by calmodulin.

The effects of non-steroidal inhibitors of phospholipase A2 on leukotriene and histamine release from human and guinea-pig lung

The effects of chloroquine and mepacrine were determined on the release of slow reacting substances (leukotrienes) from lung fragments in vitro. These drugs have been shown in a variety of tissues to inhibit phospholipase A2, and thus to reduce the availability of arachidonate, which is a substrate for leukotriene biosynthesis. Leukotriene and histamine release from unsensitized human lung was stimulated by calcium ionophore A23187, and from actively sensitized guinea-pig lung, by ovalbumin. Chloroquine (10 microM and 100 microM) significantly inhibited leukotriene release in lung from both species, and at 100 microM also inhibited histamine release. Mepacrine (10 microM) inhibited leukotriene release in human lung and at 100 microM in guinea-pig lung. The effects of chloroquine (100 microM) on leukotriene release were counteracted by the presence of arachidonic acid (10 microM), which suggests that chloroquine had impaired the availability of arachidonate. It seems probable that chloroquine and mepacrine inhibit leukotriene release by inhibition of phospholipase A2 in lung.

Calcium- and calmodulin-dependent phosphorylation of diphosphoinositide in acetylcholine receptor-rich membranes from electroplax of Narke japonica

The phosphorylation of phosphoinositides in the acetylcholine receptor (AChR)-rich membranes from the electroplax of the electric fish Narke japonica has been examined. When the AChR-rich membranes were incubated with [gamma-32P]ATP, 32P was incorporated into only two inositol phospholipids, i.e., tri- and diphosphoinositide (TPI and DPI). Even after the alkali treatment of the membrane, AChR-rich membranes still showed a considerable DPI kinase activity upon addition of exogenous DPI. It is likely that the 32P-incorporation into these lipids was realized by the membrane-bound DPI kinase and phosphatidyl inositol (PI) kinase. Such a membrane-bound DPI kinase was activated by Ca2+ (greater than 10(-6) M), whereas the PI kinase appeared to be inhibited by Ca2+. The effect of Ca2+ on the DPI phosphorylation was further enhanced by the addition of ubiquitous Ca2+-dependent regulator protein calmodulin. Calmodulin antagonists such as chlorpromazine (CPZ), trifluoperazine (TFP), and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibited the phosphorylation of DPI in the AChR-rich membranes. It is suggested that the small pool of TPI in the plasma membrane is replenished by such Ca2+- and calmodulin-dependent DPI kinase responding to the change in the intracellular Ca2+ level.

Effects of trifluoperazine on platelet activation

Previous reports of the inhibitory effects of trifluoperazine on platelet responses to different aggregating agents have been conflicting, and the mechanism of action remains unclear. We have found that aggregation by minimum concentrations of collagen and arachidonic acid, and second phase aggregation by minimum concentrations of ADP, thrombin, epinephrine and the calcium ionophore A23187 were inhibited by 40-60 microM trifluoperazine. The first phase of aggregation by a minimum concentration of epinephrine was completely inhibited by 100 microM trifluoperazine, and the first phase of aggregation induced by ADP, thrombin or A23187 was decreased by 300 microM trifluoperazine. The platelet shape change caused by collagen, but by no other aggregating agent examined, was inhibited by 300 microM trifluoperazine. Secretion of 3H-5 hydroxytryptamine by minimum concentrations of ADP, collagen, epinephrine and arachidonic acid was completely suppressed by 50 microM trifluoperazine. Secretion by thrombin and A23187 was incompletely inhibited by 300 microM trifluoperazine. Thromboxane B2 formation caused by all aggregating agents, except epinephrine, was incompletely suppressed by 50 microM trifluoperazine, and 300 microM trifluoperazine only caused complete inhibition of thromboxane B2 formation by ADP, collagen and epinephrine. The phorbol ester, TPA, which mimics diacylglycerol by activating protein kinase C, caused aggregation and secretion. Aggregation, but not secretion, by low concentrations of TPA was inhibited by concentrations of trifluoperazine as low as 50 microM. However, aggregation by a combination of TPA and A23187 was only inhibited by concentrations of trifluoperazine in excess of 100 microM. Secretion by TPA was inhibited by concentrations of trifluoperazine in excess of 200 microM. Our findings suggest that low concentrations of trifluoperazine inhibit platelet activation by inhibiting phospholipase A2, and that higher concentrations inhibit platelet responses by interfering with protein kinase C.

Malignant hyperthermia: molecular defects in membrane permeability

Malignant hyperthermia (MH), a genetically inherited disorder of skeletal muscle, is due to molecular defect in membrane permeability. The alteration in membrane permeability is suggested to be due to enhanced phospholipase A2 activity which is responsible for the increased level in sarcoplasmic Ca2+. The excess Ca2+ is responsible for muscle hyper-rigidity and enhanced rate of glycolysis, resulting in a rapid rate of lactic acid production and a low pH in MH muscle.

[Eicosanoids and phospholipases]

Prostaglandins, thromboxanes, and leukotrienes have been implicated to play an important role in physiology as well as in a growing list of pathophysiologic conditions. These oxidation products of 8.11.14-eicosatrienoic-, 5.8.11.14.-eicosatetraenoic-, and 5.8.11.14.17.-pentaenoic acids have been collectively designated eicosanoids. Many clinically important diseases are associated with altered eicosanoid biosynthesis. Furthermore, a series of hormones are known to induce acutely formation of eicosanoids, suggesting a crucial role in a multitude of tissue responses including phenomena such as secretion, platelet aggregation, chemotaxis, and smooth muscle contraction. The major precursor for the eicosanoids seems to be 5.8.11.14.-eicosatetraenoic acid or arachidonic acid. Virtually all of arachidonic acid however is present in esterified form in complex glycerolipids. Since cyclooxygenase and the lipoxygenases utilize arachidonic acid in its free form, a set of acylhydrolases is required to liberate arachidonic acid from membrane lipids before eicosanoid formation can occur. It became only recently apparent that a minor acidic phospholipid, phosphatidylinositol, comprising only 5%-10% of the phospholipid mass in mammalian cells, plays an important role in arachidonic acid metabolism. Phosphatidylinositol--after phosphorylation to phosphatidylinositolphosphate and phosphatidylinositolbisphosphate--appears to be hydrolyzed by specific phospholipases C generating 1-stearoyl-2-arachidonoyl-diglyceride. Diglyceride serves as substrate for diglyceride lipase to form monoglyceride and free fatty acid. Alternatively diglyceride is phosphorylated by diglyceride kinase yielding phosphatidic acid, which is believed to be reincorporated into phosphatidylinositol. In addition to phosphatidylinositol phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid may contribute to arachidonic acid release. These phospholipids are substrates for phospholipases A2 generating free arachidonic acid and the respective lysophospholipid. Understanding of the biochemistry of arachidonic acid liberation may be critical in developing strategies of pharmacological intervention in a variety of pathological conditions.

Role of phospholipase and calmodulin inhibitors on insulin, arachidonic acid and prostaglandin E2 release

Using several experimental approaches, we have studied simultaneously the effect of glucose upon insulin, arachidonic acid and prostaglandin E2 release by rat pancreatic islets. A 16.6 mmol/l glucose concentration stimulated the release of insulin, arachidonic acid and prostaglandins. All these effects were significantly reduced either by calmodulin and phospholipase A2 inhibitors, or by the omission of calcium in the incubation medium. Phospholipase A2 inhibitors do not modify the glucose-induced net 45Ca2+ uptake by isolated islets. Our results would suggest that activation of phospholipases, particularly A2, is involved in the mechanism by which glucose stimulates insulin release. This activation increases the intracellular concentration of arachidonic acid, prostaglandins and probably phospholipid degradation products, that could act as messengers for the stimulus-secretion coupling of insulin. The calcium-calmodulin complex would take part in this effect. Conversely, the glucose-induced net calcium uptake by the islets might either be preceded by phospholipase activation or not significantly affected by the blockade of its activity.

Increased calmodulin levels in psoriasis and low Ca++ regulated mouse epidermal keratinocyte cultures

Calcium has been shown to regulate the proliferation of epidermal keratinocytes in vitro. We became interested in the role of the calcium binding protein, calmodulin, in hyperproliferative, low calcium regulated keratinocytes in vitro and in the in vivo hyperproliferative state, psoriasis. Calmodulin levels were measured by radioimmune assay in neonatal mouse keratinocytes grown in 0.02 mM calcium (hyperproliferative) and 1.2 mM calcium (normal) media, and in cells that had been grown in low calcium medium and then switched to normal calcium. On a whole culture basis the normal cells had more calmodulin than the low calcium cells. However, when low calcium monolayers were compared to the normal basal monolayer, the low calcium hyperproliferative cells had more calmodulin. Cells that were switched from 0.02 mM calcium to 1.2 mM calcium showed increasing calmodulin levels over time. Psoriatic plaques contained 2-3 times more calmodulin than the skin of normal controls when examined on a per micrograms of DNA, per micrograms of protein, and per gram of wet weight basis. Adjacent uninvolved psoriatic skin also had significantly elevated calmodulin levels in all data bases except per microgram of protein/cm2. These data suggest that increased calmodulin levels are associated with epidermal hyperproliferation and/or with the state of differentiation.

Effects of calcium antagonists and calmodulin inhibitors on angiotensin II-induced prostaglandin productions in the isolated dog renal arteries

Angiotensin II markedly potentiated both PGE2 and PGI2 productions in the isolated dog renal arteries. This angiotensin II-induced response was significantly reduced by the treatments of EGTA and calcium antagonists such as verapamil, nifedipine and 8-(N,N'-diethylamino)-octyl-3,4,5,-trimethoxybenzoate (TMB-8). Calmodulin inhibitors, trifluoperazine and W-7 also inhibited the angiotensin II-induced PG productions while an inactive analogue of W-7, W-5 did not have any effect. The results suggest that angiotensin II may enhance the intracellular Ca2+ level through the influx of extracellular Ca2+ and then, calmodulin activated with Ca2+ will stimulate both PGE2 and PGI2 productions via its activation of phospholipase A2 in the dog renal arteries.

Effects of calmodulin antagonists and calmodulin on phospholipid base-exchange activities in rabbit platelets

Effects of various calmodulin antagonists and calmodulin on the incorporation of serine, ethanolamine and choline into the corresponding phospholipids, such as phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine by Ca2+-stimulated base-exchange reactions in rabbit platelet membranes were studied. Under a Ca2+-EGTA buffer system, the incorporation of three bases were stimulated by Ca2+ in a biphasic manner. Minimum requirement of free Ca2+ for the reactions was found to be around 0.5 microM and maximal incorporation took place at high Ca2+ concentrations (3-5 mM). Various calmodulin antagonists such as chlorpromazine, trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, not only activated the three reactions but also greatly enhanced their sensitivity to Ca2+ (K0.5, 0.1-0.3 microM). In the absence of Ca2+, however, the drugs did not show any effect on the reactions. The concentrations of the drugs required for half maximal stimulation were approx. 30-40 microM. Although platelet membranes contained endogenous calmodulin (0.3-0.6 microgram/mg of membrane protein), the addition of exogenous calmodulin inhibited choline exchange activity but had no or little effect on serine or ethanolamine exchange activity. The results suggest that in the presence of low Ca2+ concentrations, these drugs markedly stimulate base-exchange activities, and choline exchange activity may be regulated by calmodulin.

Production of prostaglandins by dispersed cells and fragments from bovine parathyroid glands

We studied the production of prostaglandins by fragments and dispersed cells from bovine parathyroid glands. Fragments released 138 +/- 19 (SE), 132 +/- 21, 4.3 +/- 0.5, and 13 +/- 6.6 pg/mg/h of 6-keto-PGF1 alpha, PGF2 alpha, PGE2, and thromboxane B2, respectively (n = 7 - 26), while dispersed cells released 414 +/- 110, 22 +/- 7.3, 27 +/- 3.8, and 29 +/- 11 pg/10(6) cells/h, respectively, of the same compounds (n = 6 - 25). Indomethacin (1 microgram/ml) inhibited the release of 6-keto-PGF1 alpha by 80-90% in fragments and cells, while mellitin stimulated release of this prostaglandin, suggesting de novo synthesis of prostaglandins in these preparations. Calcium stimulated production of 6-keto-PGF1 alpha by 1.3-fold in cells and 2.6-fold in fragments and also enhanced production of PGF2 alpha by 1.9-fold in fragments. Isoproterenol, on the other hand, had no effect on production of 6-keto-PGF1 alpha in either preparation. These results demonstrate that parathyroid tissue as well as parathyroid cells per se produce a variety of prostaglandins. We have previously shown that PGE2 and PGF2 alpha modulate cAMP accumulation and PTH release in dispersed bovine parathyroid cells. The role of the endogenous production of prostaglandins by the parathyroid gland in the acute or chronic regulation of parathyroid function, however, remains to be determined.

Inhibition of the hydro-osmotic response to vasopressin and hypertonicity by phenothiazines and W7, calmodulin antagonists

Phenothiazines and W7, calmodulin antagonists, inhibit the water flow response produced by ADH, exogenous cyclic AMP, phosphodiesterase inhibition and serosal hypertonicity. Calmodulin antagonists had no effect on osmotic water movement in the absence of hormone. Calmodulin was isolated and localized by immunofluorescence in bladder epithelial cells. Phenothiazines inhibited toad bladder calmodulin activation of phosphodiesterase and prevented fluorescent antibody recognition. The results suggest that the calcium-calmodulin process plays a role in the hydro-osmotic response to ADH and that produced by serosal hypertonicity. The calmodulin common site occurs subsequent to cyclic AMP formation, perhaps on the microtubule-microfilament system.

Characterization of a Ca2+-stimulated lipid peroxidizing system in the sea urchin egg

Addition of calcium chloride to an egg homogenate of Strongylocentrotus purpuratus stimulates O2 consumption which is not inhibited by millimolar cyanide. Results strongly suggest that Ca2+-stimulated O2 consumption is at least partially the result of polyunsaturated fatty acid oxidation. First, addition of arachidonic acid (AA), or other polyunsaturated fatty acids, to the homogenate enhance Ca2+-stimulated O2 consumption; this enhancement, by AA, being coupled to its oxidation to a hydroxy fatty acid. Second, calcium stimulates a lipase activity in the homogenate that is capable of releasing free fatty acids. Third, Ca2+-stimulated O2 consumption and AA oxidation have virtually identical calcium requirements and pH optima. The sequence of events then is that upon calcium addition to the homogenate, lipase activity is increased which liberates free fatty acids. At the same time calcium also activates a polyunsaturated fatty acid oxygenase, possibly lipoxygenase, that converts the free fatty acids to hydroxy fatty acids. The possible physiological importance of this reaction is underscored by the high affinity for Ca2+ [approximately 10(-7)M], an ion known to increase above the required levels at fertilization. The pH activity profile also suggests possible physiological modulation because a pH change of 6.8 increasing to 7.2, as suggested to occur after fertilization, yields almost a twofold increase in O2 consumption. Egg homogenates from many other invertebrate species have the ability to oxidize AA in a Ca2+-dependent fashion. For the investigated species, the presence of Ca2+-stimulated O2 consumption and AA oxidation correlates with the presence of cyanide insensitive respiration in the intact egg.

Trifluoperazine abolishes the actions of bradykinin on glucose 1,6-bisphosphate levels and on the activities of glucose 1,6-bisphosphatase, phosphofructokinase and phosphoglucomutase

Injection of trifluoperazine abolished the bradykinin-induced decrease in intracellular concentration of glucose 1,6-bisphosphate (Glc-1,6-P2) in rat tibialis anterior muscle and skin. These changes in Glc-1,6-P2 levels may be attributed to the changes in the activity of glucose 1,6-bisphosphatase (the enzyme that degrades Glc-1,6-P2), which was markedly enhanced by bradykinin and reversed by trifluoperazine. Concomitantly to the changes in Glc-1,6-P2, the potent activator of phosphofructokinase and phosphoglucomutase, the activities of these enzymes were reduced by bradykinin and restored by trifluoperazine. These findings suggest that trifluoperazine treatment may have a beneficial effect on the depressed glycolysis induced by bradykinin in tissue damage.

Mechanism of action of angiotensin II and bradykinin on prostaglandin synthesis and vascular tone in the isolated rat kidney. Effect of Ca++ antagonists and calmodulin inhibitors

We have studied the effect of angiotensin II and bradykinin on prostaglandin output and vascular tone during extracellular calcium depletion and administration of calcium antagonists and calmodulin inhibitors to elucidate the mechanism of action in the isolated rat kidney perfused with Tyrode's solution. Administration of angiotensin II (0.028-0.28 nmol) or bradykinin (0.28-2.8 nmol) enhanced the output of prostaglandin E2 and 6-keto-prostaglandin F1 alpha in a dose-dependent manner. Angiotensin II, but not bradykinin, produced renal vasoconstriction. Omission of calcium from the medium or infusion of calcium entry blockers, diltiazem (60 microM), or nimodipine (47 microM), failed to alter prostaglandin output elicited by angiotensin II or bradykinin; however, the effect of angiotensin II to produce renal vasoconstriction was inhibited. If calcium was omitted from the medium, the intracellular calcium antagonists, 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (23 microM), dantrolene sodium (31 microM), or ryanodine (2 microM), attenuated prostaglandin output caused by angiotensin II but not bradykinin. Calmodulin inhibitors, trifluoperazine (2 microM), napthalene sulfonamide hydrochloride (2 microM), or calmidazolium (2 microM), diminished prostaglandin output elicited by angiotensin II, but not that caused by bradykinin. Trifluoperazine, but not naphthalene sulfonamide or calmidazolium, attenuated the renal vasoconstrictor effect of angiotensin II. Prostaglandin output induced by angiotensin II and bradykinin were inhibited by mepacrine and indomethacin, whereas, the prostaglandin output caused by exogenous arachidonic acid (33 nmol) was abolished by indomethacin but was unaltered by mepacrine, calcium antagonists, and calmodulin inhibitors. From these data, we conclude that angiotensin II produces renal vasoconstriction by a mechanism dependent on extracellular calcium but not calmodulin, whereas angiotensin II-induced prostaglandin output depends on intracellular calcium and calmodulin. In contrast, bradykinin appears to stimulate prostaglandin synthesis by a calcium/calmodulin-independent mechanism.

Differential effects of trifluoperazine on arachidonate liberation, secretion and myosin phosphorylation in intact platelets

Gel-filtered platelets prelabeled with [3H]-arachidonate and [14C]-adenine or [32P]-orthophosphate were stimulated with thrombin in the presence of various concentrations of trifluoperazine (TFP). Based on the presence of [14C]- or [32P]-labeled extracellular adenine nucleotides, TFP, above 50 microM, caused platelet lysis which reached 30-40% at 100 microM. In the non-lytic range (0-50 microM) TFP caused marked inhibition of [3H]-arachidonic acid liberation and [3H]-phosphatidylcholine breakdown which was complete at 25 microM. Breakdown of [3H]-phosphatidylinositol was partially (about 50%) inhibited at 25 microM TFP and little further inhibition occurred above this concentration. These results show that thrombin-induced liberation of [3H]-arachidonic acid occurs entirely by a TFP-sensitive mechanism, and suggest that the major portion of the arachidonate is liberated from phosphatidylcholine with a possible contribution from phosphatidylinositol. Dense granule secretion and acid hydrolase secretion were progressively inhibited by TFP, while the thiazine had only a small effect on phosphorylation of myosin. These results indicate that the inhibition of the secretory processes by TFP is not caused by action of TFP on myosin light chain kinase. It is suggested that the profound effect of TFP on arachidonic acid liberation but not myosin phosphorylation is due to different subcellular localization of these calmodulin-requiring enzymes: phospholipase A2 and myosin light chain kinase. The lipophilic TFP dissolves preferentially in the membranes where it has access to phospholipase A2 but not to myosin light chain kinase.