Role of protein kinase A in the regulation of cytosolic free calcium in human osteoblast-like SaOS-2 cells

Simvastatin reduces adrenal catecholamine secretion evoked by stimulation of cholinergic nicotinic and angiotensinergic AT1 receptors

We investigated the influence of simvastatin, a statin, on the secretion of catecholamines (CA) in rat adrenal glands, and clarified its action mechanism. Simvastatin suppressed acetylcholine (ACh)-evoked CA release in a dose- and time-dependent fashion. In the presence of simvastatin, CA secretion evoked by 1.1-dimethyl-4-phenyl piperazinium iodide (DMPP), angiotensin II, high K⁺, veratridine, and Bay-K-8644 was time-dependently inhibited. However, in the simultaneous presence of simvastatin and Nω-nitro-L-arginine methyl ester hydrochloride, CA secretion evoked by angiotensin II and DMPP recovered to control levels. Adrenal NO release was increased by simvastatin-treatment. Simvastatin-inhibited CA secretion was not affected by treatment with mevalonate. Pravastatin did not influence ACh-evoked CA secretion, while atorvastatin reduced it. In the simultaneous presence of simvastatin and fimasartan, ACh-induced CA release was markedly reduced compared to that of fimasartan-treatment alone. We present the first evidence that simvastatin reduces adrenal CA secretion induced by stimulation of nicotinic and AT₁-receptors. Simvastatin-induced inhibition seems to involve reducing the influx of both Ca²⁺ and Na⁺ into adrenochromaffin cells, partly via the elevation of NO production by NO synthase activation, without inhibition of 3-hydroxy-methylglutaryl coenzyme A reductase. Co-administration of simvastatin and fimasartan may be clinically helpful for the treatment of cardiovascular diseases.

Upregulation of Neuronal Nitric Oxide Synthase mRNA and Protein in Adrenal Medulla of Water-deprived Rats

Experiments were performed to investigate whether adrenal neuronal nitric oxide synthase (nNOS) mRNA and protein expression are responsive to alterations in body volume. Using an RT-PCR technique, the relative quantities of nNOS mRNA as well as the tyrosine hydroxylase and phenylethanolamine N-methyltransferase mRNA in the adrenals of water-deprived rats significantly increased from 12 hr to 4 days. In situ hybridization and immunohistochemical study showed that water deprivation activated nNOS mRNA and protein expression in the adrenal medulla. Four days after water deprivation, nNOS protein expression determined by Western blot significantly increased in the adrenal gland. Our results are the first to demonstrate that nNOS syntheses in the adrenal medulla are markedly increased in water-deprived rats. This study also indicates that the upregulation of nNOS synthesis of the adrenal medulla is associated with the activation of adrenal medullary function in the face of volume depletion.

Inhibitory effects of ginsenoside-rb2 on nicotinic stimulation-evoked catecholamine secretion

The aim of the present study was to investigate whether ginsenoside-Rb2 (Rb2) can affect the secretion of catecholamines (CA) in the perfused model of the rat adrenal medulla. Rb2 (3~30 µM), perfused into an adrenal vein for 90 min, inhibited ACh (5.32 mM)-evoked CA secretory response in a dose- and time-dependent fashion. Rb2 (10 µM) also time-dependently inhibited the CA secretion evoked by DMPP (100 µM, a selective neuronal nicotinic receptor agonist) and high K(+) (56 mM, a direct membrane depolarizer). Rb2 itself did not affect basal CA secretion (data not shown). Also, in the presence of Rb2 (50 µg/mL), the secretory responses of CA evoked by veratridine (a selective Na(+) channel activator (50 µM), Bay-K-8644 (an L-type dihydropyridine Ca(2+) channel activator, 10 µM), and cyclopiazonic acid (a cytoplasmic Ca(2+)-ATPase inhibitor, 10 µM) were significantly reduced, respectively. Interestingly, in the simultaneous presence of Rb2 (10 µM) and L-NAME (an inhibitor of NO synthase, 30 µM), the inhibitory responses of Rb2 on ACh-evoked CA secretory response was considerably recovered to the extent of the corresponding control secretion compared with the inhibitory effect of Rb2-treatment alone. Practically, the level of NO released from adrenal medulla after the treatment of Rb2 (10 µM) was greatly elevated compared to the corresponding basal released level. Collectively, these results demonstrate that Rb2 inhibits the CA secretory responses evoked by nicotinic stimulation as well as by direct membrane-depolarization from the isolated perfused rat adrenal medulla. It seems that this inhibitory effect of Rb2 is mediated by inhibiting both the influx of Ca(2+) and Na(+) into the adrenomedullary chromaffin cells and also by suppressing the release of Ca(2+) from the cytoplasmic calcium store, at least partly through the increased NO production due to the activation of nitric oxide synthase, which is relevant to neuronal nicotinic receptor blockade.

Polyphenols of Rubus coreanum Inhibit Catecholamine Secretion from the Perfused Adrenal Medulla of SHRs

The present study was attempted to investigate whether polyphenolic compounds isolated from wine, which is brewed from Rubus coreanum Miquel (PCRC), may affect the release of catecholamines (CA) from the isolated perfused adrenal medulla of the spontaneously hypertensive rats (SHRs), and to establish its mechanism of action. PCRC (20~180 microg/ml) perfused into an adrenal vein for 90 min relatively dose-dependently inhibited the CA secretory responses to ACh (5.32 mM), high K(+) (56 mM), DMPP (100 microM) and McN-A-343 (100 microM). PCRC itself did not affect basal CA secretion (data not shown). Also, in the presence of PCRC (60 microg/ml), the CA secretory responses to veratridine (a selective Na(+) channel activator (10 microM), Bay-K-8644 (a L-type dihydropyridine Ca(2+) channel activator, 10 microM), and cyclopiazonic acid (a cytoplasmic Ca(2+) -ATPase inhibitor, 10 microM) were significantly reduced, respectively. In the simultaneous presence of PCRC (60 microg/ml) and L-NAME (an inhibitor of NO synthase, 30 microM), the inhibitory responses of PCRC on the CA secretion evoked by ACh, high K(+), DMPP, and Bay-K-8644 were considerably recovered to the extent of the corresponding control secretion compared with that of PCRC-treatment alone. The level of NO released from adrenal medulla after the treatment of PCRC (60 microg/ml) was greatly elevated compared with the corresponding basal level. Taken together, these results demonstrate that PCRC inhibits the CA secretion from the isolated perfused adrenal medulla of the SHRs evoked by stimulation of cholinergic receptors as well as by direct membrane-depolarization. It seems that this inhibitory effect of PCRC is mediated by blocking the influx of calcium and sodium into the adrenal medullary chromaffin cells of the SHRs as well as by inhibition of Ca(2+) release from the cytoplasmic calcium store at least partly through the increased NO production due to the activation of NO synthase.

Provinol inhibits catecholamine secretion from the rat adrenal medulla

The aim of the present study was to examine the effect of provinol, which is a mixture of polyphenolic compounds from red wine, on the secretion of catecholamines (CA) from isolated perfused rat adrenal medulla, and to elucidate its mechanism of action. Provinol (0.3~3 microg/ml) perfused into an adrenal vein for 90 min dose- and time-dependently inhibited the CA secretory responses evoked by ACh (5.32 mM), high K(+) (a direct membrane-depolarizer, 56 mM), DMPP (a selective neuronal nicotinic N(N) receptor agonist, 100 microM) and McN-A-343 (a selective muscarinic M(1) receptor agonist, 100 microM). Provinol itself did not affect basal CA secretion. Also, in the presence of provinol (1 microg/ml), the secretory responses of CA evoked by Bay-K-8644 (a voltage-dependent L-type dihydropyridine Ca(2+) channel activator, 10 microM), cyclopiazonic acid (a cytoplasmic Ca(2+)-ATPase inhibitor, 10 microM) and veratridine (an activator of voltage-dependent Na(+) channels, 10 microM) were significantly reduced. Interestingly, in the simultaneous presence of provinol (1 microg/ml) plus L-NAME (a selective inhibitor of NO synthase, 30 microM), the CA secretory responses evoked by ACh, high K(+), DMPP, McN-A-343, Bay-K-8644 and cyclpiazonic acid recovered to the considerable extent of the corresponding control secretion in comparison with the inhibition of provinol-treatment alone. Under the same condition, the level of NO released from adrenal medulla after the treatment of provinol (3 microg/ml) was greatly elevated in comparison to its basal release. Taken together, these data demonstrate that provinol inhibits the CA secretory responses evoked by stimulation of cholinergic (both muscarinic and nicotinic) receptors as well as by direct membrane-depolarization from the perfused rat adrenal medulla. This inhibitory effect of provinol seems to be exerted by inhibiting the influx of both calcium and sodium into the rat adrenal medullary cells along with the blockade of Ca(2+) release from the cytoplasmic calcium store at least partly through the increased NO production due to the activation of nitric oxide synthase.

Resveratrol inhibits nicotinic stimulation-evoked catecholamine release from the adrenal medulla

Resveratrol has been known to possess various potent cardiovascular effects in animal, but there is little information on its functional effect on the secretion of catecholamines (CA) from the perfused model of the adrenal medulla. Therefore, the aim of the present study was to determine the effect of resveratrol on the CA secretion from the isolated perfused model of the normotensive rat adrenal gland, and to elucidate its mechanism of action. Resveratrol (10~100microM) during perfusion into an adrenal vein for 90 min inhibited the CA secretory responses evoked by ACh (5.32 mM), high K(+) (a direct membrane-depolarizer, 56 mM), DMPP (a selective neuronal nicotinic N(n) receptor agonist, 100microM) and McN-A-343 (a selective muscarinic M(1) receptor agonist, 100microM) in both a time- and dose-dependent fashion. Also, in the presence of resveratrol (30microM), the secretory responses of CA evoked by veratridine 8644 (an activator of voltage-dependent Na(+) channels, 100microM), Bay-K-8644 (a L-type dihydropyridine Ca(2+) channel activator, 10microM), and cyclopiazonic acid (a cytoplasmic Ca(2+)-ATPase inhibitor, 10microM) were significantly reduced. In the simultaneous presence of resveratrol (30microM) and L-NAME (an inhibitor of NO synthase, 30microM), the CA secretory evoked by ACh, high K(+) , DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid were recovered to a considerable extent of the corresponding control secretion compared with the inhibitory effect of resveratrol alone. Interestingly, the amount of nitric oxide (NO) released from the adrenal medulla was greatly increased in comparison to its basal release. Taken together, these experimental results demonstrate that resveratrol can inhibit the CA secretory responses evoked by stimulation of cholinergic nicotinic receptors, as well as by direct membrane-depolarization in the isolated perfused model of the rat adrenal gland. It seems that this inhibitory effect of resveratrol is exerted by inhibiting an influx of both ions through Na(+) and Ca(2+) channels into the adrenomedullary cells as well as by blocking the release of Ca(2+) from the cytoplasmic calcium store, which are mediated at least partly by the increased NO production due to the activation of NO synthase.

The mechanism of cyclic nucleotide hydrolysis in the phosphodiesterase catalytic site

The cyclic nucleotide phosphodiesterase superfamily of enzymes (PDEs) catalyzes the stereospecific hydrolysis of the second messengers adenosine and guanosine 3',5'- cyclic monophosphate (cAMP, cGMP) to produce 5'-AMP and 5'-GMP, respectively. The PDEs are targets of high-throughput screening to determine selective inhibitors for a variety of therapeutic purposes. The catalytic pocket where the hydrolysis takes place is a highly conserved region and has several residues which are absolutely conserved across the PDE families. In this study, we consider a model cyclic substrate in which the adenine/guanine base has been replaced with a hydrogen atom, and we present results of a quantum computational investigation of the hydrolysis reaction as it occurs within the PDE catalytic site using the ONIOM hybrid (B3LYP/6-31g(d):PM3) method. We characterize the bound substrate, the bound hydrolyzed product, and the transition state which connects them for our model cyclic substrate placed in a truncated model of the PDE4D2 catalytic site. We address the role that the conserved histidine proximal to the bimetal system of the catalytic site, along with its conserved glutamine partner, plays in the generation of the hydroxide nucleophile. Our study provides computational evidence for several key features of the cAMP/cGMP hydrolysis mechanism as it occurs within the protein environment across the PDE superfamily.

Enhanced umbilical blood flow during acute hypoxemia after chronic umbilical cord compression: a role for nitric oxide

BACKGROUND

The continuing incidence of intrapartum morbidity may be partly due to antenatal compromise, which influences the fetal defense to labor and delivery. We have shown that antenatal exposure of the ovine fetus to partial compression of the umbilical cord suppresses femoral vasoconstriction during subsequent acute hypoxemia through elevated nitric oxide (NO) activity. This study investigated whether elevated NO activity in cord-compressed fetuses enhanced the vasodilator response to hypoxemia in circulations in which blood flow is known to increase during acute hypoxemia, such as the umbilical vascular bed.

METHODS AND RESULTS

Fifteen fetal sheep were chronically instrumented between 117 and 120 days of gestation with vascular catheters and an umbilical flow probe. In 8 of these fetuses, umbilical blood flow was reduced by 30% for 3 days between 125 and 128 days. The remaining 7 fetuses acted as sham-operated controls. Between 2 and 7 days after umbilical cord/sham compression, fetuses were exposed to 2 episodes of acute hypoxemia, on separate days, during infusion with either saline or treatment with a combination of NG-nitro-l-arginine methyl ester and sodium nitroprusside. The data show that umbilical cord compression significantly enhances the umbilical hyperemia through NO-dependent mechanisms during a subsequent episode of acute hypoxemia.

CONCLUSIONS

Increased fetal NO activity after chronic cord compression has opposing effects in circulations that either constrict or dilate during subsequent acute hypoxemia. The data imply that antenatal compromise switches the fetal strategy to withstand episodes of subsequent acute hypoxemia of the type that may occur during labor and delivery from a reliance on vasoconstrictor mechanisms to those promoting NO-dependent vasodilation.

Synthesis and structure-activity relationships of cis-tetrahydrophthalazinone/pyridazinone hybrids: a novel series of potent dual PDE3/PDE4 inhibitory agents

In this study, the synthesis and in vitro and in vivo pharmacological investigations of a new series of phthalazinone/pyridazinone hybrids with both PDE3 and PDE4 inhibitory activities are described. These compounds combine the pharmacophores of recently discovered 4a,5,8,8a-tetrahydro-2H-phthalazin-1-one-type inhibitors of PDE4 and the well-known 2H-pyridazin-3-one-type PDE3 inhibitors such as the tetrahydrobenzimidazoles. Most of the synthesized compounds are pharmacologically spoken PDE3/PDE4 hybrids. All hybrids show potent PDE4 inhibitory activity (pIC(50) = 7.0-8.7), whereas the pIC(50) values for inhibition of PDE3 vary from 5.4 to 7.5. In general, analogues with a 5-methyl-4,5-dihydropyridazinone moiety exhibit the highest PDE3 inhibitory activities. The highest in vivo antiinflammatory activity is displayed by phthalazinones 43 and 44 showing, at a dose of 30 micromol/kg po, 46% inhibition of arachidonic acid (AA) induced mouse ear edema. No correlation was found between the in vitro PDE3 and/or PDE4 inhibitory activity and the in vivo antiinflammatory capacity after oral dosing.

Effect of extracellular volume expansion and surgical stress on splanchnic blood flow and cardiac output in anesthetized rats: role of nitric oxide

In a normal volume state, surgical stress decreases rather than increases nitric oxide (NO) production in the vascular system. In our studies, the effect of minor and major surgical stress and three different degrees of volume expansion on systemic and splanchnic circulatory parameters and on the NO dependence of the circulation have been investigated. When the degree of volume expansion was increased, cardiac output and organ blood flow increased without significant change in vascular resistances. Major surgical stress reduced the increase in cardiac output and organ blood flow elicited by the volume expansion. NO synthase (NOS) inhibition significantly increased blood pressure and total peripheral resistance (TPR) and decreased cardiac output in all groups of animals. As the degree of volume expansion was increased, the NO dependence of the circulation in the surgically less- and more-stressed animals was inversely influenced in some cases. With the three degrees of volume expansion (20, 40, and 60 ml/kg), the NOS inhibition increased the TPR from 30.7 R/kg +/- 1.90 to 73.6 R/kg +/- 5.00, from 20.7 R/kg +/- 1.43 to 66.7 R/kg +/- 3.88, and from 19.9 R/kg +/- 1.25 to 49.1 R/kg +/- 3.84 in the surgically less-stressed animals and from 38.6 R/kg +/- 2.14 to 59.8 R/kg +/- 5.62, from 31.9 R/kg +/- 2.70 to 81.7 R/kg +/- 9.89, and from 29.1 R/kg +/- 2.49 to 91.1 R/kg +/- 6.36 in the surgically more-stressed animals. Volume expansion increases the NO dependence of the vascular resistance in the surgically more-stressed animals but decreases it in the surgically less-stressed animals.

Adverse intrauterine conditions diminish the fetal defense against acute hypoxia by increasing nitric oxide activity

BACKGROUND

The incidence of perinatal morbidity arising from birth hypoxia or asphyxia has not changed significantly in recent years despite marked improvements in labor management. Perinatal mortality in these circumstances may therefore reflect antenatal compromise and subsequent alteration of the fetal capacity to respond to episodes of hypoxia that may occur during labor. Hence, we have investigated the effects of fetal pre-exposure to a period of adverse intrauterine conditions on the mechanisms mediating the fetal defense response to a subsequent episode of acute hypoxia in sheep.

METHODS AND RESULTS

Sixteen fetal sheep were chronically instrumented at 118+/-2 days for recording of blood pressure, heart rate, and femoral and umbilical blood flows. In 8 of these fetuses, umbilical blood flow was reduced by 30% for 3 days (between days 125 and 128). The remaining 8 fetuses acted as sham-operated controls. Between 2 and 7 days after umbilical cord/sham compression, all fetuses were exposed to 2 episodes of acute hypoxemia on separate days during infusion with either saline or treatment with a combination of N(G)-nitro-L-arginine methyl ester and sodium nitroprusside. We show that previous fetal exposure to a period of adverse intrauterine conditions, such as that induced by compression of the umbilical cord, elevates nitric oxide activity and results in a markedly diminished cardiovascular defense response to subsequent acute hypoxia.

CONCLUSIONS

The data imply that pre-exposure to adverse antenatal conditions may render the fetus more susceptible to the acute hypoxia or asphyxia that can accompany relatively uncomplicated labor and delivery.

Novel selective PDE4 inhibitors. 1. Synthesis, structure-activity relationships, and molecular modeling of 4-(3,4-dimethoxyphenyl)-2H-phthalazin-1-ones and analogues

A number of 6-(3,4-dimethoxyphenyl)-4,5-dihydro-2H-pyridazin-3-ones and a novel series of 4-(3,4-dimethoxyphenyl)-2H-phthalazin-1-ones were prepared and tested on the cGMP-inhibited phosphodiesterase (PDE3) and cAMP-specific phosphodiesterase (PDE4) enzymes. All tested compounds were found to specifically inhibit PDE4 except for pyridazinone 3b, which showed moderate PDE4 (pIC(50) = 6.5) as well as PDE3 (pIC(50) = 6.6) inhibitory activity. In both the pyridazinone and phthlazinone series it was found that N-substitution is beneficial for PDE4 inhibition, whereas in the pyridazinone series it also accounts for PDE4 selectivity. In the phthalazinone series, the cis-4a,5,6,7,8,8a-hexahydrophthalazinones and their corresponding 4a,5,8,8a-tetrahydro analogues showed potent PDE4 inhibitory potency (10/11c,d: pIC(50) = 7.6-8.4). A molecular modeling study revealed that the cis-fused cyclohexa(e)ne rings occupy a region in space different from that occupied by the other fused (un)saturated hydrocarbon rings applied; we therefore assume that the steric interactions of these rings with the binding site play an important role in enzyme inhibition.

New insights into interactions between the human PTH/PTHrP receptor and agonist/antagonist binding

We prepared a polyclonal antiserum [Ab-(88-97)] against residues 8-97 of the NH2-terminal tail of the human (h) parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor. Ab-(88-97) bound specifically to the receptor, as assessed by fluorescence-activated cell sorter analysis of HEK C21 cells, which stably express approximately 400,000 hPTH/PTHrP receptors per cell. Unlike PTH, Ab-(88-97) binding did not elicit either adenosine 3',5'-cyclic monophosphate or intracellular calcium concentration signaling responses in these cells. Incubation of C21 cells for 90 min at 4 degrees C with hPTH-(1-34) plus antiserum reduced the Ab-(88-97) binding to the cells by up to 40-50% of control values in a PTH concentration-dependent fashion with a half-maximal effective concentration of approximately 5 nM. The decrease in Ab-(88-97) binding caused by hPTH-(1-34) was completely reversed by coincubation with hPTHrP-(7-34). We conclude that residues 88-97 of the hPTH/PTHrPR are involved, either directly or indirectly, in agonist but not antagonist binding to the receptor.

Effect of hemocarboperfusion on organ blood flow and survival in porcine endotoxic shock

OBJECTIVE

To evaluate the effects of hemocarboperfusion on hemodynamics, organ blood flow, and survival in endotoxin shock.

DESIGN

Prospective, placebo-controlled, animal trial.

SETTING

Research laboratory in a major university teaching hospital.

SUBJECTS

Pentobarbital-anesthetized pigs.

INTERVENTIONS

Twenty-eight pentobarbital-anesthetized pigs (18.5 to 22.3 kg) received 100 micrograms/kg of Escherichia coli endotoxin (lipopolysaccharide 0127) over 30 mins. Group 1 animals (n = 14) were controls and had blood diverted through an extracorporeal circuit without activated charcoal for 60 mins after lipopolysaccharide infusion. Group 2 animals (n = 14) underwent nonpulsatile hemocarboperfusion (activated charcoal SCN-1K).

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure, cardiac output, systemic vascular resistance, mean pulmonary arterial pressure, pulmonary vascular resistance, oxygen delivery, and regional blood flow (radiolabeled microsphere technique) were determined at baseline and every 30 mins for 150 mins. Results are presented as mean +/- SD. Parameters in the two groups were compared by two-way analysis of variance. A p < .05 was considered significant. The survival rate was ten (71%) of 14 animals in group 1 compared with 14 (100%) of 14 animals in group 2 (p < .05, Fisher's exact test). The mean cardiac output at the end of hemocarboperfusion was 1.6 +/- 0.6 L/min in group 1 compared with 3.0 +/- 0.9 L/min in group 2, and remained lower in group 1 animals throughout the experiment. Pulmonary arterial pressure and pulmonary vascular resistance were lower in the hemocarboperfusion-treated animals during and after hemocarboperfusion. Systemic vascular resistance increased by 70% after lipopolysaccharide infusion and returned to baseline values in the hemocarboperfusion group but remained increased in controls. Oxygen delivery was lower in group 1 at 90 and 150 mins (287 +/- 34 vs. 478 +/- 48 mL/min and 251 +/- 24 vs. 356 +/- 21 mL/min, respectively). Blood flow rates to the brain (38.5 +/- 7.5 vs. 27.1 +/- 5.4 mL/min/100 g), large intestine (26.6 +/- 1.1 vs. 17.7 +/- 2.5 mL/ min/100 g), and adrenal cortex (200 +/- 45 vs. 139 +/- 41 mL/min/100 g) were higher in the hemocarboperfusion group at the completion of carboperfusion but not at later time points.

CONCLUSION

These data suggest that hemocarboperfusion may be of value in the treatment of septic shock.

Role of protein kinase C alpha, Arf, and cytoplasmic calcium transients in phospholipase D activation by sodium fluoride in osteoblast-like cells

The effect of fluoride on phospholipase D (PLD) activation was studied using in vitro culture of Saos-2, MG-63 osteosarcoma cells, and normal osteoblast-like cells derived from human bone explants. Millimolar concentrations of NaF induced a significant accumulation of phosphatidylethanol (PEt) in Saos-2 cells but not in MG-63 and normal osteoblast-like cells. PLD activation was evident at 15 mM and concentration-dependent up to 50 mM. This stimulation was inhibited by deferoxamine, a chelator of Al3+, suggesting that PLD activation involves fluoride-sensitive G proteins. A good correlation was found between the levels of intracellular free Ca2+ and the activation of PLD. The time courses of the two responses were nearly identical. The ability of NaF to induce both responses was largely dependent on the presence of extracellular calcium. The calcium ionophore A23187 reproduced the effect of NaF, and this effect was antagonized by EGTA, suggesting that PLD activation was, at least in part, a calcium-regulated event. Phorbol 12-myristate 13-acetate (PMA) also stimulated PLD activity in human bone cells. Protein kinase C alpha (PKC alpha) and epsilon were expressed in Saos-2 cells. Acute pretreatment of cells with PMA reduced concomitantly the amounts of PKC alpha, but not of PKC epsilon, and the subsequent activation of PLD elicited by PKC activators. The PLD response to NaF was not attenuated but rather enhanced by down-regulation of PKC alpha. Therefore, PKC-alpha-induced PLD activation is unlikely to mediate the effect of NaF. Moreover, PMA and NaF showed a supraadditive effect on PLD activation in Saos-2 cells. This stimulation, in contrast to NaF alone, was not reduced by EGTA. Hence, mobilization of calcium by NaF cannot account for the enhanced PLD activation in response to PMA stimulation. Membrane Arf and RhoA contents were assessed by Western immunoblot analyses. Membranes derived from NaF-stimulated Saos-2 cells contained more Arf and RhoA when compared with membranes derived from control or PMA-stimulated cells. Translocation of the small GTPases was calcium-independent. We conclude that PLD activation by NaF in Saos-2 cells includes a fluoride-sensitive G protein, increases in the levels of intracellular calcium, and Arf/RhoA redistribution to membranes. The results also indicate that the NaF-induced Arf/RhoA translocation exerts in concert with PMA-activated PKC alpha a synergistic effect on the activation of PLD in Saos-2 cells.

Regional blood flow alterations after bovine fumaryl beta beta-crosslinked hemoglobin transfusion and nitric oxide synthase inhibition

OBJECTIVES

a) To determine whether isovolemic exchange transfusion with cell-free, bovine fumaryl beta beta-crosslinked hemoglobin results in a different pattern of regional blood flow distribution than transfusion with a poor oxygen-carrying, colloidal solution. b) Because of potential nitric oxide scavenging by plasma-based hemoglobin, to determine whether blood flow differences are reduced after nitric oxide synthase inhibition.

DESIGN

A prospective, randomized design with repeated blood flow measurements within groups.

SETTING

Experimental physiology laboratory in a university medical center.

SUBJECTS

Pentobarbital-anesthetized female cats.

INTERVENTIONS

Three groups of eight cats were studied: a) a control group with no transfusion (hematocrit of 32%); b) an anemia group in which exchange transfusion with an albumin-containing solution reduced hematocrit to 18% over a 40- to 50-min period; and c) a group in which cell-free hemoglobin was exchanged transfused to reduce hematocrit to 18%, without a proportional reduction in oxygen-carrying capacity. Bovine hemoglobin was covalently crosslinked intramolecularly between the 81-lysine residues on the beta-subunits to stabilize the tetramer. Regional blood flow was measured by the radiolabeled microsphere technique before transfusion and at 10, 100, and 180 mins from the start of transfusion. At 190 mins, N omega-nitro-L-arginine methyl ester (L-NAME; 10mg/kg) was infused to inhibit nitric oxide synthase and blood flow was measured 30 mins later.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure was unchanged in the control and albumin-transfused groups. However, mean arterial pressure increased rapidly in the hemoglobin-transfused group. With hemoglobin transfusion, there were marked reductions in blood flow to the intestines, kidneys and adrenal glands. Administration of L-NAME after hemoglobin transfusion failed to increase arterial pressure or cause further reductions in intestinal, renal, or adrenal blood flow. Administration of L-NAME to the control and albumin-transfused groups increased arterial pressure and reduced intestinal, renal, and adrenal blood flows to values attained with hemoglobin transfusion. In contrast, in skeletal muscle and left ventricle, blood flow rates increased in the albumin-transfused group and were greater than those values found in the control group and hemoglobin-transfused group. The greater flow in the albumin-transfused group persisted after L-NAME administration. There was no difference in renal sodium, potassium, or osmolar excretion, or in urine flow between groups.

CONCLUSIONS

Transfusion with cell-free, bovine crosslinked hemoglobin in cats can selective reductions in blood flow in the intestines, kidneys, and adrenal glands without evidence of renal dysfunction by a mechanism consistent with nitric oxide scavenging. In skeletal and cardiac muscle, the increase in blood flow persisted after nitric oxide inhibition in the albumin group relative to the hemoglobin-transfused group at equivalent hematocrit values. This finding is consistent with compensatory vasoconstriction with hemoglobin transfusion due to improved oxygenation by this oxygen carrier.

Inositol 1-,4-,5-trisphosphate-dependent Ca2+ signaling by the recombinant human PTH/PTHrP receptor stably expressed in a human kidney cell line

We previously reported the preparation and partial characterization of a series of human embryonic kidney cell lines (HEK-293) stably expressing various numbers of the recombinant human (h) parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor (Rc). Using this expression system we examined ligand (PTH or PTHrP) binding characteristics and cyclic AMP responsiveness. We have now extended these studies to investigate the calcium signal transduction pathways activated by the hPTH/PTHrP Rc. In parental HEK-293 cells, which lack endogenous PTH/PTHrP Rc, incubation with hPTH(1-34) had no effect on cytosolic free Ca2+ concentration [Ca2+]i. In HEK-293 clone C-21, stably expressing approximately 400,000 Rc/cell, PTH stimulated an increase in [Ca2+]i by Ca2+ release from intracellular stores; PTH released Ca2+ exclusively from the IP3 sensitive Ca2+ pool. Unlike previous studies, the ability of PTH to elicit both cAMP responses and [Ca2+]i transients occurred over a wide range of Rc numbers (between 400,000 and 3000 Rc/cell); both responses were always observed at PTH concentrations in the same dose range although the magnitude of the responses decrease with Rc number. Pretreatment of C-21 cells with pertussis toxin for 24 h, which significantly enhanced PTH-stimulated cAMP accumulation, did not modulate PTH-stimulated [Ca2+]i transients. At each PTH concentration tested which resulted in increased cAMP levels, there was also an increase in [Ca2+]i transients. Treatment of C-21 cells with a battery of midregion and C-terminal PTH or PTHrP peptides showed no effect on either [Ca2+]i transients or cAMP accumulation, indicating a lack of functional interactions between these peptides and the form of the hPTH/PTHrP Rc stably expressed in these cells. Immunological analysis of G-protein expression demonstrated the presence of Gs, Gi, and Gq in all parental and transfected cells lines examined. Taken together, these data demonstrate that the hPTH/PTHrP Rc, stably expressed in HEK-293 cells, elicits responses in both the cAMP and IP3-dependent [Ca2+]i pathways and is responsive only to N-terminal PTH/PTHrP peptides.