Epoxyeicosatrienoic acids activate K+ channels in coronary smooth muscle through a guanine nucleotide binding protein

Epoxyeicosatrienoic acids (EETs) are endothelium-derived arachidonic acid metabolites of cytochrome P450. They dilate coronary arteries, open K+ channels, and hyperpolarize vascular smooth muscles. However, the mechanisms of these smooth muscle actions remain unknown. This study examined the effects of EETs on the large-conductance Ca(2+)-activated K+ channel (KCa) in smooth muscle cells of small bovine coronary arteries. In cell-attached patch-clamp experiments, 11,12-EET produced a 0.5- to 10-fold increase in the activity of the KCa channels when added in concentrations of 1, 10, and 100 nmol/L. In the inside-out excised membrane patch mode, 11,12-EET was without effect on the activity of the KCa channel unless GTP (0.5 mmol/L) or GTP and ATP (1 mmol/L) were added to the bath solution. In the presence of GTP and ATP, the increase in the KCa channel activity with 11,12-EET in inside-out patches was comparable to that in cell-attached patches. This effect of 11,12-EET in inside-out patches was blocked by the addition of GDP-beta-S (100 mumol/L). In outside-out patches, 11,12-EET also increased the KCa channel activity when GTP and ATP were added to the pipette solution. The addition of a specific anti-Gs alpha antibody (100 nmol/L) in the pipette solution completely blocked the activation of the KCa channels induced by 11,12-EET. An anti-G beta gamma or anti-Gi alpha antibody was without effect. We conclude that 11,12-EET activates the KCa channels by a Gs alpha-mediated mechanism. This mechanism contributes to the effects of EETs as endothelium-derived hyperpolarizing factors to hyperpolarize and relax arterial smooth muscle.

TraI, a LuxI homologue, is responsible for production of conjugation factor, the Ti plasmid N-acylhomoserine lactone autoinducer

Conjugal transfer of the nopaline-type Agrobacterium Ti plasmid pTiC58 is regulated by a transcriptional activator, TraR, and a diffusible signal molecule, conjugation factor (CF). CF is a member of a family of substituted homoserine lactones (HSLs) that act as coinducers for regulating gene expression in diverse Gram-negative bacteria by a mechanism called autoinduction. In Vibrio fischeri HSL production is conferred by the luxI gene. Homologues of this gene are responsible for HSL production by other Gram-negative bacteria. A gene that we call traI, conferring production of material with CF activity, was localized to a 1-kb region at the upstream end of tra3 of pTiC58. Spectroscopy showed that the activity was authentic CF. Sequence analysis showed that traI could encode a protein of 211 amino acids, TraI, that is related to the proteins responsible for HSL production by other bacteria. A second, partial open reading frame immediately downstream of traI could encode a protein related to TrbB of plasmid RP4, which is required for conjugal transfer. Transcription of traI and of the downstream tra3 genes requires TraR and CF and initiates from the traI promoter. The results show that traI is responsible for CF production, that it is the first gene of the tra3 operon, and that expression of this operon is regulated by autoinduction.

Characteristics and superoxide-induced activation of reconstituted myocardial mitochondrial ATP-sensitive potassium channels

Mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels have been suggested as triggers and end effectors in myocardial ischemic preconditioning. However, the intracellular mechanism regulating mitoK(ATP) channels remains unclear. In the present study, mitoK(ATP) channels from bovine ventricular myocardium were reconstituted using planar lipid bilayers, and the effect of superoxide (O(2-.)) on the activity of these reconstituted channels was examined. After incorporation, a potassium-selective current was recorded. The mean conductance of this current was 56 pS at 150 mmol/L KCl, which was substantially inhibited by 1 mmol/L MgATP. 5-Hydroxydecanoate (5-HD, 10 to 100 micromol/L), a selective mitoK(ATP) antagonist, reduced the open state probability (NPo) of these channels in a concentration-dependent manner, whereas diazoxide (10 micromol/L), a selective mitoK(ATP) agonist, significantly increased channel activity. HMR-1098 (100 micromol/L), a selective sarcolemmal K(ATP) antagonist, had no effect on the activity of reconstituted channels. Addition of xanthine/xanthine oxidase (100 micromol/L per 0.038 U/mL), an O(2-.)-generating system, resulted in a marked activation of mitoK(ATP) channels; the NPo of the channels was increased from 0.60+/-0.10 to 1.94+/-0.02. This O(2)(-.)-induced channel activation was completely abolished by pretreatment with 5-HD (100 micromol/L) or a sulfhydryl alkylating compound, N-ethylmaleimide (2 mmol/L). It is concluded that myocardial mitoK(ATP) channels can be reconstituted into lipid bilayers and that O(2-.) activates these channels. The effect of O(2-.) may be associated with its direct action on the sulfhydryl groups of the channel protein.

TraG from RP4 and TraG and VirD4 from Ti plasmids confer relaxosome specificity to the conjugal transfer system of pTiC58

Plasmid conjugation systems are composed of two components, the DNA transfer and replication system, or Dtr, and the mating pair formation system, or Mpf. During conjugal transfer an essential factor, called the coupling protein, is thought to interface the Dtr, in the form of the relaxosome, with the Mpf, in the form of the mating bridge. These proteins, such as TraG from the IncP1 plasmid RP4 (TraG(RP4)) and TraG and VirD4 from the conjugal transfer and T-DNA transfer systems of Ti plasmids, are believed to dictate specificity of the interactions that can occur between different Dtr and Mpf components. The Ti plasmids of Agrobacterium tumefaciens do not mobilize vectors containing the oriT of RP4, but these IncP1 plasmid derivatives lack the trans-acting Dtr functions and TraG(RP4). A. tumefaciens donors transferred a chimeric plasmid that contains the oriT and Dtr genes of RP4 and the Mpf genes of pTiC58, indicating that the Ti plasmid mating bridge can interact with the RP4 relaxosome. However, the Ti plasmid did not mobilize transfer from an IncQ relaxosome. The Ti plasmid did mobilize such plasmids if TraG(RP4) was expressed in the donors. Mutations in traG(RP4) with defined effects on the RP4 transfer system exhibited similar phenotypes for Ti plasmid-mediated mobilization of the IncQ vector. When provided with VirD4, the tra system of pTiC58 mobilized plasmids from the IncQ relaxosome. However, neither TraG(RP4) nor VirD4 restored transfer to a traG mutant of the Ti plasmid. VirD4 also failed to complement a traG(RP4) mutant for transfer from the RP4 relaxosome or for RP4-mediated mobilization from the IncQ relaxosome. TraG(RP4)-mediated mobilization of the IncQ plasmid by pTiC58 did not inhibit Ti plasmid transfer, suggesting that the relaxosomes of the two plasmids do not compete for the same mating bridge. We conclude that TraG(RP4) and VirD4 couples the IncQ but not the Ti plasmid relaxosome to the Ti plasmid mating bridge. However, VirD4 cannot couple the IncP1 or the IncQ relaxosome to the RP4 mating bridge. These results support a model in which the coupling proteins specify the interactions between Dtr and Mpf components of mating systems.

The replicator of the nopaline-type Ti plasmid pTiC58 is a member of the repABC family and is influenced by the TraR-dependent quorum-sensing regulatory system

The replicator (rep) of the nopaline-type Ti plasmid pTiC58 is located adjacent to the trb operon of this conjugal element. Previous genetic studies of this region (D. R. Gallie, M. Hagiya, and C. I. Kado, J. Bacteriol. 161:1034-1041, 1985) identified functions involved in partitioning, origin of replication and incompatibility, and copy number control. In this study, we determined the nucleotide sequence of a 6,146-bp segment that encompasses the rep locus of pTiC58. The region contained four full open reading frames (ORFs) and one partial ORF. The first three ORFs, oriented divergently from the traI-trb operon, are closely related to the repA, repB, and repC genes of the octopine-type Ti plasmid pTiB6S3 as well as to other repA, -B, and -C genes from the Ri plasmid pRiA4b and three large plasmids from Rhizobium spp. The fourth ORF and the partial ORF are similar to y4CG and y4CF, respectively, of the Sym plasmid pNGR234a. The 363-bp intergenic region between traI and repA contained two copies of the tra box which is the cis promoter recognition site for TraR, the quorum-sensing activator of Ti plasmid conjugal transfer. Expression of the traI-trb operon from the tra box II-associated promoter mediated by TraR and its acyl-homoserine lactone ligand, AAI, was negatively influenced by an intact tra box III. On the other hand, the region containing the two tra boxes was required for maximal expression of repA, and this expression was enhanced slightly by TraR and AAI. Copy number of a minimal rep plasmid increased five- to sevenfold in strains expressing traR but only when AAI also was provided. Consistent with this effect, constitutive expression of the quorum-sensing system resulted in an apparent increase in Ti plasmid copy number. We conclude that Ti plasmid copy number is influenced by the quorum-sensing system, suggesting a connection between conjugal transfer and vegetative replication of these virulence elements.

The conjugal transfer system of Agrobacterium tumefaciens octopine-type Ti plasmids is closely related to the transfer system of an IncP plasmid and distantly related to Ti plasmid vir genes

We have determined the DNA sequences of two unlinked regions of octopine-type Ti plasmids that contain genes required for conjugal transfer. Both regions previously were shown to contain sequences that hybridize with tra genes of the nopaline-type Ti plasmid pTiC58. One gene cluster (designated tra) contains a functional oriT site and is probably required for conjugal DNA processing, while the other gene cluster (designated trb) probably directs the synthesis of a conjugal pilus and mating pore. Most predicted Tra and Trb proteins show relatively strong sequence similarity (30 to 50% identity) to the Tra and Trb proteins of the broad-host-range IncP plasmid RP4 and show significantly weaker sequence similarity to Vir proteins found elsewhere on the Ti plasmid. An exception is found in the Ti plasmid TraA protein, which is predicted to be a bifunctional nickase-helicase that has no counterpart in IncP plasmids or among Vir proteins but has homologs in at least six other self-transmissible and mobilizable plasmids. We conclude that this Ti plasmid tra system evolved by acquiring genes from two or three different sources. A similar analysis of the Ti plasmid vir region indicates that it also evolved by appropriating genes from at least two conjugal transfer systems. The widely studied plasmid pTiA6NC previously was found to be nonconjugal and to have a 12.65-kb deletion of DNA relative to other octopine-type Ti plasmids. We show that this deletion removes the promoter-distal gene of the trb region and probably accounts for the inability of this plasmid to conjugate.

11,12-Epoxyeicosatrienoic acid stimulates endogenous mono-ADP-ribosylation in bovine coronary arterial smooth muscle

The role of endogenous ADP-ribosylation in mediating the activation of the Ca(2+)-activated K(+) channels was determined in bovine coronary arteries. Endogenous ADP-ribosylation was examined by incubating coronary arterial homogenates or lysates of cultured coronary arterial smooth muscle cells with [adenylate-(32)P]NAD. Four (32)P-labeled proteins were observed at 51, 52, 80, and 124 kDa in the homogenates and lysates. This reaction was enhanced by the addition of 11,12-epoxyeicosatrienoic acid (11,12-EET), a cytochrome P450-derived eicosanoid, and GTP to the incubation. By Western blot analysis, 42- and 70-kDa proteins were recognized by specific antibodies against ADP-ribosyltransferase in the coronary arterial homogenates and smooth muscle cell lysate but not in the lysate of endothelial cells. The 52-kDa acceptor protein of endogenous ADP-ribosylation comigrated with a protein ADP-ribosylated by cholera toxin and was recognized and immunoprecipitated by an anti-G(S)alpha antibody. These results suggest that G(S)alpha is one of several acceptors of the ADP-ribose moiety. As shown by the patch-clamp technique, 11,12-EET stimulated the activation of the K(+) channels in the smooth muscle cells, and this activation was completely blocked by novobiocin, vitamin K(1), 3-aminobenzamide, and m-iodobenzylguanidine, inhibitors of endogenous mono-ADP-ribosyltransferases. We conclude that endogenous mono-ADP-ribosyltransferases are present in smooth muscle from bovine coronary arteries. These enzymes transfer ADP-ribose to the cellular proteins such as G(S)alpha and may mediate intracellular signal transduction in coronary vascular smooth muscle. In the coronary circulation, the ADP-ribosylation signaling pathway may play an important role in mediating the activation of the K(+) channels induced by 11,12-EET.

Effect of chronic salt loading on adenosine metabolism and receptor expression in renal cortex and medulla in rats

Previous studies have shown that chronic salt loading increased renal interstitial adenosine concentrations and desensitized renal effects of adenosine, a phenomenon that could facilitate sodium excretion. However, the mechanisms responsible for the increased adenosine production and decreased adenosine response are poorly understood. This study examined the effects of the dietary high salt intake on adenosine metabolism and receptor expression in the renal cortex and medulla in Sprague Dawley rats. Fluorescent high-performance liquid chromatography analyses were performed to determine adenosine levels in snap-frozen kidney tissues. Comparing rats fed a normal (1% NaCl) versus high salt (4% NaCl) diet, renal adenosine concentrations in rats fed a high salt diet were significantly higher (cortex: 43+/-3 versus 85+/-4, P<0.05; medulla: 183+/-4 versus 302+/-8 nmol/g wet tissue, P<0.05). Increased adenosine concentrations were not associated with changes in the 5'-nucleotidase or adenosine deaminase activity, as determined by quantitative isoelectric focusing and gel electrophoresis. Western blot analyses showed that a high salt diet (4% NaCl for 3 weeks) downregulated A1 receptors (antinatriuretic type), did not alter A2A and A2B receptors (natriuretic type), and upregulated A3 receptors (function unknown) in both renal cortex and medulla. The data show that stimulation of adenosine production and downregulation of A1 receptors with salt loading may play an important role in adaptation in the kidney to promote sodium excretion.

Regulation of potassium channels in coronary arterial smooth muscle by endothelium-derived vasodilators

Recent studies have suggested that coronary endothelial cells produce and release nitric oxide (NO), prostaglandin I2, and epoxyeicosatrienoic acids (EETs). These endothelium-derived vasodilators play an important role in the control of coronary vascular tone. However, the mechanism by which these endothelium-derived vasodilators cause relaxation of coronary arterial smooth muscle has yet to be determined. This study characterized and compared the effects of NO, prostaglandin I2, and 11,12-EET on the two main types of potassium channels in small bovine coronary arterial smooth muscle: the large conductance Ca(2+)-activated K+ channels (KCa) and 4-aminopyridine-sensitive delayed rectifier K+ channels (Kdrf). In cell-attached patches, nonoate, an NO donor, activated both KCa and Kdrf channels. The open probability of both KCa and Kdrf channels increased 10- to 25-fold when nonoate was added to the bath at concentrations of 10(-6) to 10(-4) mol/L. 11,12-EET (10(-8) to 10(-4) mol/L) also increased the activity of the KCa channels in a concentration-dependent manner, but it had no effect on the activity of the Kdrf channels, even in the highest concentration studied (10(-4) mol/L). In contrast to the effect of 11,12-EET, iloprost, a prostaglandin I2 analogue (10(-6) to 10(-4) mol/L), produced a concentration-dependent increase in the activity of Kdrf channels without affecting the KCa channels. In conclusion, all three endothelium-derived vasodilators act to open potassium channels; however, the channel types that they affect are different. NO activates both KCa and Kdrf channels; 11,12-EET activates only the KCa channels; and prostaglandin I2 activates only the Kdrf channels.

Potentiation of baroreceptor reflex response by heat shock protein 70 in nucleus tractus solitarii confers cardiovascular protection during heatstroke

BACKGROUND

Whereas hypotension and bradycardia seen during the onset of heatstroke may be protected by prior induction of heat shock protein 70 (HSP70) in the brain, the underlying mechanism is not fully understood. We evaluated the hypothesis that HSP70 may confer cardiovascular protection during heatstroke by potentiating the baroreceptor reflex (BRR) control of peripheral hemodynamic performance.

METHODS AND RESULTS

Adult male Sprague-Dawley rats subjected to a brief hyperthermic heat shock (HS; 42 degrees C for 15 minutes) induced discernible expression of HSP70 in the bilateral nucleus tractus solitarii (NTS), the terminal site in the brain stem for primary baroreceptor afferents. This HSP70 expression was detected at 8 hours, peaked at 24 hours, and returned to baseline by 48 hours after HS. Brief hyperthermia also significantly potentiated the BRR response in a temporal profile that correlated positively with changes in HSP70 expression at the NTS. Prior HS also appreciably alleviated hyperthermia, severe hypotension, and bradycardia manifested during the onset of heatstroke (45 degrees C for 60 minutes) elicited 24 hours later. Microinjection bilaterally of anti-HSP70 antiserum (1:20) into the NTS or denervation of the sinoaortic baroreceptor afferents significantly reversed the enhancement of BRR response and cardiovascular protection during heatstroke induced by prior HS.

CONCLUSIONS

These results suggest that HS-induced expression of HSP70 in the NTS may alleviate severe hypotension and bradycardia exhibited during the onset of heatstroke by potentiating both the sensitivity and capacity of BRR response.

Production and metabolism of ceramide in normal and ischemic-reperfused myocardium of rats

Ceramide has been shown to be a key signaling molecule involved in the apoptotic effect of tumor necrosis factor alpha (TNF-alpha) and other cytokines. Given the importance of cytokines such as TNF-alpha in myocardial ischemia-reperfusion injury, we hypothesize that ceramide is increased during ischemia or reperfusion, and that the activity of enzymes responsible for its production or breakdown should be increased and/or decreased, respectively. Therefore, in the present study, we characterized the enzymatic activities responsible for ceramide production and metabolism in the myocardium of rats, and determined the contribution of these enzymes to altered ceramide levels during myocardial ischemia and reperfusion. The basal ceramide concentration in the myocardium of rats was 34.0 pmol/mg tissue. As determined by the conversion of 14C-sphingomyelin into ceramide and 14C-choline phosphate, both neutral (N-) and acidic (A-) SMase were detected in the myocardium, with a conversion rate of 0.09 +/- 0.008 and 0.32 +/- 0.05 nmol/min per mg protein, respectively. The activity of A-SMase (78 % of total cellular activity) was significantly higher in microsomes than in cytosol, while the activity of N-SMase was similar in both fractions. Ceramidase, a ceramide-metabolizing enzyme, was also detected in the myocardium of rats. It metabolized ceramide into sphingosine at a rate of 9.94 +/- 0.42 pmol/min per mg protein. In anesthetized rats, 30 min of ischemia had no apparent effect on ceramide concentrations in the myocardium, while 30 min of ischemia followed by 3 h of reperfusion resulted in a significant increase in ceramide by 48 %. The activities of both N- and A-SMase were reduced by 44 % and 32 %, respectively, in the myocardium subjected to ischemia followed by reperfusion, but unaltered in the ischemic myocardium. It was also found that myocardial ischemia followed by reperfusion produced a marked inhibition of ceramidase (by 29 %). These results demonstrate that the myocardium of rats expresses N- and A-SMase and ceramidase, which contribute to the production and metabolism of ceramide, respectively. Tissue ceramide concentrations increased in reperfused myocardium. These increases in ceramide were not associated with enhanced SMase activity, but rather with reduced ceramidase activity.

The results at ten years of the Insall-Burstein II total knee replacement. Clinical, radiological and survivorship studies

We reviewed the outcome of 146 Insall-Burstein II total knee replacements carried out in 121 patients over a period of nearly four years in a general orthopaedic unit. At a mean follow-up of ten years, 94 knees in 78 patients were available for review. Six patients (7 knees) were lost to follow-up and 37 (45 knees) had died. The clinical outcome using the scoring system of the Hospital for Special Surgery (HSS) was excellent or good in 79% of patients, fair in 14% and poor in 7%. The mean preoperative HSS score was 31, improving to 79 at the latest review. Using the newer rating system of the Knee Society, the mean score at ten years was 87 and the mean functional score 56. The arc of flexion improved from a mean preoperative value of 88 degrees to 100 degrees. The 18 patients who had had a previous high tibial osteotomy were analysed separately and were found to have benefited equally from the operation. Nine prostheses were revised, giving a cumulative survival rate of 92.3% at ten years. Radiological evaluation of 104 radiographs showed radiolucent lines around ten tibial components, none of which required revision. Anterior knee pain was a significant problem.

Ceramide reduces endothelium-dependent vasodilation by increasing superoxide production in small bovine coronary arteries

Ceramide serves as a second messenger in a variety of mammalian cells. Little is known regarding the role of ceramide in the regulation of vascular endothelial function. The present study was designed to determine whether ceramide affects endothelium-dependent vasodilation in coronary arteries and to explore the mechanism of action of ceramide. In isolated and pressurized small bovine coronary arteries, cell-permeable C(2)-ceramide (10(-)(5) mol/L) markedly attenuated vasodilator responses to bradykinin and A23187 (by 40% and 60%, respectively). In the presence of K(G)-nitro-L-arginine methyl ester, ceramide produced no further inhibition on the vasodilation induced by these vasodilators. Ceramide had no effect on DETA NONOate-induced vasodilation. By use of a fluorescence NO indicator (4,5-diaminofluorescein diacetate), intracellular NO was measured in the endothelium of freshly isolated small coronary arteries. It was found that ceramide significantly inhibited bradykinin-induced NO increase within endothelial cells. However, it had no effect on the activity of arterial or endothelial NO synthase. Pretreatment of the arteries with sodium dihydroxybenzene disulfonate (Tiron, 10(-)(3) mol/L), a cell-permeable superoxide scavenger, or polyethylene glycol superoxide dismutase (100 U/mL) largely restored the inhibitory effects of ceramide on the vasodilation and NO increase induced by bradykinin or A23187. Moreover, ceramide time-dependently increased intracellular superoxide (O(2)(-. )) in the endothelium, as measured by a fluorescent O(2)(-. )indicator, dihydroethidium. These results demonstrate that ceramide inhibits endothelium-dependent vasodilation in small coronary arteries by decreasing NO in vascular endothelial cells and that this decrease in NO is associated with increased O(2)(-. ) but not with the inhibition of NO synthase activity within these cells.

Barriers to meeting the mental health needs of the Chinese community

BACKGROUND

This study aimed to identify the barriers encountered by Chinese people with mental health needs in England which hindered their obtaining appropriate help from the National Health Service (NHS).

METHODS

Attenders at Chinese community centres in health authority districts with resident Chinese population in excess of 2000 were invited to fill in a 12-item Chinese Health Questionnaire (12-CHQ). Individuals who scored two or above, indicating a high probability of a mental health problem, were invited to undertake a semi-structured interview.

RESULTS

A total of 401 completed the 12-CHQ. Eighty-six (21.4 per cent) screened positive and 71 (82.6 per cent) agreed to be interviewed. Although 70 (98.6 per cent) were registered with a general practitioner (GP), there were long delays before they made contact with health professionals, and the GP was the first port of call for help in only 27 (38.6 per cent) interviewees. Fifty-two (74.3 per cent) had encountered difficulties when they sought professional help. The main barriers were language, interviewees' perceptions of symptoms as somatic rather than psychiatric in origin, lack of knowledge about statutory services, and lack of access to bilingual health professionals. Doctors, particularly GPs, were pivotal in the management of their conditions. The majority were prescribed psychiatric medication with only a small number in contact with community psychiatric services. Unemployment and social exclusion were common. Stigma associated with mental illness and limited knowledge in the community were identified as the causes for the widespread discrimination experienced by the interviewees.

CONCLUSION

The mental health needs of these Chinese people were not adequately met by statutory services, nor could they rely on family and friends for care and support. Training for health service staff and access to health advocates are essential to maximize the effectiveness of health professional-patient contacts. The promotion of better understanding of mental illness by the Chinese community is important, and greater flexibility within the NHS is required to ensure those professionals with bilingual skills are used to the best effect.

The superantigen streptococcal pyrogenic exotoxin C (SPE-C) exhibits a novel mode of action

Recombinant streptococcal pyrogenic exotoxin C (SPE-C) is a potent superantigen that stimulates Vbeta2-bearing human T cells, but is inactive in mice. SPE-C binds with high affinity to both human HLA-DR and murine I-E molecules, but not to murine I-A molecules in a zinc-dependent fashion. Competition binding studies with other recombinant toxins revealed that SPE-C lacks the generic low affinity major histocompatibility complex (MHC) class II alpha-chain binding site common to all other bacterial superantigens. Despite this, SPE-C cross-links MHC class II to induce homotypic aggregation of class II-bearing B cells. Nondenaturing sodium dodecyl sulfate electrophoresis and size exclusion chromatography revealed that both wild-type and recombinant SPE-C exist in a stable dimer at neutral or alkaline pH. These data support a recent crystal structure of SPE-C and reveal yet another mechanism by which bacterial superantigens ligate and cross-link MHC class II.

Role of renal medullary adenosine in the control of blood flow and sodium excretion

This study determined the levels of adenosine in the renal medullary interstitium using microdialysis and fluorescence HPLC techniques and examined the role of endogenous adenosine in the control of medullary blood flow and sodium excretion by infusing the specific adenosine receptor antagonists or agonists into the renal medulla of anesthetized Sprague-Dawley rats. Renal cortical and medullary blood flows were measured using laser-Doppler flowmetry. Analysis of microdialyzed samples showed that the adenosine concentration in the renal medullary interstitial dialysate averaged 212 +/- 5.2 nM, which was significantly higher than 55.6 +/- 5.3 nM in the renal cortex (n = 9). Renal medullary interstitial infusion of a selective A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 300 pmol. kg-1. min-1, n = 8), did not alter renal blood flows, but increased urine flow by 37% and sodium excretion by 42%. In contrast, renal medullary infusion of the selective A2 receptor blocker 3, 7-dimethyl-1-propargylxanthine (DMPX; 150 pmol. kg-1. min-1, n = 9) decreased outer medullary blood flow (OMBF) by 28%, inner medullary blood flows (IMBF) by 21%, and sodium excretion by 35%. Renal medullary interstitial infusion of adenosine produced a dose-dependent increase in OMBF, IMBF, urine flow, and sodium excretion at doses from 3 to 300 pmol. kg-1. min-1 (n = 7). These effects of adenosine were markedly attenuated by the pretreatment of DMPX, but unaltered by DPCPX. Infusion of a selective A3 receptor agonist, N6-benzyl-5'-(N-ethylcarbonxamido)adenosine (300 pmol. kg-1. min-1, n = 6) into the renal medulla had no effect on medullary blood flows or renal function. Glomerular filtration rate and arterial pressure were not changed by medullary infusion of any drugs. Our results indicate that endogenous medullary adenosine at physiological concentrations serves to dilate medullary vessels via A2 receptors, resulting in a natriuretic response that overrides the tubular A1 receptor-mediated antinatriuretic effects.

Oxidative stress enhances the production and actions of adenosine in the kidney

The purpose of this study was to determine whether superoxide anions (O.) activate 5'-nucleotidase (5'-ND), thereby increasing the production of renal adenosine and regulating renal function. Using HPLC analysis, we found that incubation of renal tissue homogenate with the O. donor KO(2) doubled adenosine production and increased the maximal reaction velocity of 5'-ND from 141 to 192 nmol. min(-1). mg protein(-1). The O.-generating system, xanthine/xanthine oxidase increased the maximal reaction velocity of 5'-ND from 122 to 204 nmol. min(-1). mg protein(-1). Superoxide dismutase (SOD) with catalase produced a concentration-dependent reduction of 5'-ND activity in renal tissue homogenate, while the SOD inhibitor diethyldithiocarbamic acid significantly increased 5'-ND activity. Inhibition of disulfide bond formation by thioredoxin or thioredoxin reductase significantly decreased xanthine/xanthine oxidase-induced activation of renal 5'-ND. In in vivo experiments, inhibition of SOD by diethyldithiocarbamic acid (0.5 mg. kg(-1). min(-1) iv) enhanced renal vasoconstriction induced by endogenously produced adenosine and increased renal tissue adenosine concentrations under control condition and in ischemia and reperfusion. We conclude that oxidative stress activates 5'-ND and increases adenosine production in the kidney and that this redox regulatory mechanism of adenosine production is important in the control of renal vascular tone and glomerular perfusion.

Genetic and sequence analysis of the pTiC58 trb locus, encoding a mating-pair formation system related to members of the type IV secretion family

Conjugal transfer of pTiC58 requires two regions, tra which contains the oriT and several genes involved in DNA processing and a region of undefined size and function that is located at the 2-o'clock position of the plasmid. Using transposon mutagenesis with Tn3HoHo1 and a binary transfer system, we delimited this second region, called trb, to an 11-kb interval between the loci for vegetative replication and nopaline catabolism. DNA sequence analysis of this region identified 13 significant open reading frames (ORFs) spanning 11,003 bp. The first, encoding traI, already has been described and is responsible for the synthesis of Agrobacterium autoinducer (AAI) (I. Hwang, P.-L. Li, L. Zhang, K. R. Piper, D. M. Cook, M. E. Tate, and S. K. Farrand, Proc. Natl. Acad. Sci. USA 91:4639-4643, 1994). Translation products of the next 11 ORFs showed similarities to those of trbB, -C, -D, -E, -J, -K, -L, -F, -G, -H, and -I of the trb region of the octopine-type Ti plasmid pTi15955 and of the tra2 core region of RP4. In RP4, these genes encode mating-pair formation functions and are essential for the conjugal transfer of the IncP plasmid. Each of the trb gene homologues is oriented counterclockwise on the Ti plasmid. Expression of these genes, as measured by using the lacZ fusions formed by Tn3HoHo1, required the traI promoter and the transcriptional activator TraR along with its coinducer, AAI. While related to that of RP4, the trb system of pTiC58 did not allow propagation of the trb-specific bacteriophages PRD1, PRR1, and Pf3. The products of several trb genes of the Ti plasmid are similar to those of other loci that encode DNA transfer or protein secretion systems, all of which are members of the type IV secretion family.

cADP-ribose activates reconstituted ryanodine receptors from coronary arterial smooth muscle

The present study was designed to test the hypothesis that cADP-ribose (cADPR) increases Ca(2+) release through activation of ryanodine receptors (RYR) on the sarcoplasmic reticulum (SR) in coronary arterial smooth muscle cells (CASMCs). We reconstituted RYR from the SR of CASMCs into planar lipid bilayers and examined the effect of cADPR on the activity of these Ca(2+) release channels. In a symmetrical cesium methanesulfonate configuration, a 245 pS Cs(+) current was recorded. This current was characterized by the formation of a subconductance and increase in the open probability (NP(o)) of the channels in the presence of ryanodine (0.01-1 microM) and imperatoxin A (100 nM). A high concentration of ryanodine (50 microM) and ruthenium red (40-80 microM) substantially inhibited the activity of RYR/Ca(2+) release channels. Caffeine (0.5-5 mM) markedly increased the NP(o) of these Ca(2+) release channels of the SR, but D-myo-inositol 1,4,5-trisphospate and heparin were without effect. Cyclic ADPR significantly increased the NP(o) of these Ca(2+) release channels of SR in a concentration-dependent manner. Addition of cADPR (0.01 microM) into the cis bath solution produced a 2.9-fold increase in the NP(o) of these RYR/Ca(2+) release channels. An eightfold increase in the NP(o) of the RYR/Ca(2+) release channels (0.0056 +/- 0.001 vs. 0.048 +/- 0.017) was observed at a concentration of cADPR of 1 microM. The effect of cADPR was completely abolished by ryanodine (50 microM). In the presence of cADPR, Ca(2+)-induced activation of these channels was markedly enhanced. These results provide evidence that cADPR activates RYR/Ca(2+) release channels on the SR of CASMCs. It is concluded that cADPR stimulates Ca(2+) release through the activation of RYRs on the SR of these smooth mucle cells.

Essential components of the Ti plasmid trb system, a type IV macromolecular transporter

The trb operon from pTiC58 is one of three loci that are required for conjugal transfer of this Ti plasmid. The operon, which probably codes for the mating bridge responsible for pair formation and DNA transfer, contains 12 genes, 11 of which are related to genes from other members of the type IV secretion system family. The 12th gene, traI, codes for production of Agrobacterium autoinducer (AAI). Insertion mutations were constructed in each of the 12 genes, contained on a full-length clone of the trb region, using antibiotic resistance cassettes or a newly constructed transposon. This transposon, called mini-Tn5Ptrb, was designed to express genes downstream of the insertion site from a promoter regulated by TraR and AAI. Each mutation could trans complement downstream Tn3HoHo1 insertions in the trb operon of full-sized Ti plasmids. When marker-exchanged into the transfer-constitutive Ti plasmid pTiC58DeltaaccR mutations in trbB, -C, -D, -E, -L, -F, -G, and -H abolished conjugal transfer from strain UIA5, which lacks the 450-kb catabolic plasmid pAtC58. However, these mutants retained residual conjugal transfer activity when tested in strain NT1, which contains this large plasmid. The trbJ mutant failed to transfer at a detectable frequency from either strain, while the trbI mutant transferred at very low but detectable levels from both donors. Only the trbK mutant was unaffected in conjugal transfer from either donor. Transfer of each of the marker-exchange mutants was restored by a clone expressing only the wild-type allele of the corresponding mutant trb gene. An insertion mutation in traI abolished the production of AAI and also conjugal transfer. This defect was restored by culturing the mutant donor in the presence of AAI. We conclude that all of the trb genes except trbI and trbK are essential for conjugal transfer of pTiC58. We also conclude that mutations in any one of the trb genes except traI and trbJ can be complemented by functions coded for by pAtC58.

Inhibition of cADP-ribose formation produces vasodilation in bovine coronary arteries

cADP-ribose (cADPR) induces the release of Ca(2+) from the intracellular stores of coronary artery smooth muscle cells. However, little is known about the role of cADPR-mediated intracellular Ca(2+) release in the control of vascular tone. The present study examined the effects of nicotinamide, a specific inhibitor of ADP-ribosylcyclase, on the vascular tone of bovine coronary arteries. A bovine coronary artery homogenate stimulated the conversion of nicotinamide guanine dinucleotide into cGDP-ribose, which is a measure of ADP-ribosylcyclase activity. Nicotinamide significantly inhibited the formation of cGDP-ribose in a concentration-dependent manner: at a concentration of 10 mmol/L, it reduced the conversion rate from 3.34+/-0.11 nmol. min(-1). mg(-1) of protein in control cells to 1.42+/-0.11 nmol. min(-1). mg(-1) of protein in treated cells, a 58% reduction. In U46619-precontracted coronary artery rings, nicotinamide produced concentration-dependent relaxation. Complete relaxation with nicotinamide occurred at a dose of 8 mmol/L; the median inhibitory concentration (IC(50)) was 1.7 mmol/L. In the presence of a cell membrane-permeant cADPR antagonist, 8-bromo-cADPR, nicotinamide-induced vasorelaxation was markedly attenuated. Pretreatment of the arterial rings with ryanodine (50 micromol/L) significantly blunted the vasorelaxation response to nicotinamide. However, iloprost- and adenosine-induced vasorelaxation was not altered by 8-bromo-cADPR. Moreover, nicotinamide significantly attenuated KCl- or Bay K8644-induced vasoconstriction by 60% and 70%, respectively. These results suggest that the inhibition of cADPR formation by nicotinamide produces vasorelaxation and blunts KCl- and Bay K8644-induced vasoconstriction in coronary arteries and that the cADPR-mediated Ca(2+) signaling pathway plays a role in the control of vascular tone in coronary circulation.

Ti plasmid conjugation is independent of vir: reconstitution of the tra functions from pTiC58 as a binary system

Two regions of the nopaline-type Ti plasmid pTiC58 are important for conjugal transfer of this element to recipient bacteria. These two regions were cloned into two independent replicons to produce a binary transfer system. For one region, oriT/tra, we constructed two derivatives, pFRtra and pDCtra-5. Each contains the oriT site and the two flanking, divergently transcribed tra operons that encode the DNA processing functions associated with the relaxosome. These two plasmids also carry traR, which encodes the transcriptional activator necessary for expression of transfer genes. The two plasmids differ by the amounts of traB sequence or sequence downstream of traG present in the construct. The second replicon, pPLE2, carries the traI/trb region. The traI gene confers production of the Agrobacterium tumefaciens N-acyl homoserine lactone autoinducer, while the remaining genes in the trb operon encode components of the mating bridge. Donors harboring the two plasmids mobilized the transfer of the plasmid carrying the oriT/tra region to an A. tumefaciens recipient at frequencies similar to that at which the intact Ti plasmid transferred. Plasmid pFRtra, which encodes most of traB, was mobilized at a frequency almost 10-fold higher than was pDCtra-5, which lacks most of the gene. A. tumefaciens donors also mobilized pFRtra to Escherichia coli and Pseudomonas fluorescens recipients at frequencies similar to those observed with A. tumefaciens recipients. Rhizobium meliloti harboring the binary system also transferred the oriT/tra component to these recipients. However, E. coli or P. fluorescens donors harboring the binary system did not transfer pFRtra to any of the recipients. Furthermore, while the A. tumefaciens and R. meliloti donors produced high levels of the autoinducer, the P. fluorescens and E. coli donors produced only trace amounts of this signal molecule. These results indicate that the tra system of pTiC58 is fully contained within the characterized tra and trb regions of the Ti plasmid, that conjugation does not require functions encoded by the vir system for maximal activity, and that while the Ti plasmid tra system recognizes diverse gram-negative bacteria as recipients, of the hosts tested, it functions only in members of the family Rhizobiaceae.

Oxygen-dependent expression of hypoxia-inducible factor-1alpha in renal medullary cells of rats

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a transcription factor that regulates the oxygen-dependent expression of a number of genes. This transcription factor may contribute to the abundant expression of many genes in renal medullary cells that function normally under hypoxic conditions. The present study was designed to determine the characteristics of HIF-1alpha cDNA cloned from the rat kidney and the expression profile of HIF-1alpha in different kidney regions and to explore the mechanism activating or regulating HIF-1alpha expression in renal medullary cells. A 3,718-bp HIF-1alpha cDNA from the rat kidney was first cloned and sequenced using RT-PCR and TA cloning technique. It was found that 823 amino acids deduced from this renal HIF-1alpha cDNA had 99%, 96%, and 90% identity with rat, mouse, or human HIF-1alpha deposited in GenBank, respectively. The 3'-untranslated region of HIF-1alpha mRNA from the rat kidney contained seven AUUUA instability elements, five of which were found to be conserved among rat, mouse, and human HIF-1alpha. Northern blot analyses demonstrated a corticomedullary gradient of HIF-1alpha mRNA expression in the kidney, with the greatest abundance in the renal inner medulla. Western blot analyses also detected a higher HIF-1alpha protein level in the nuclear extracts from the renal medulla than the renal cortex. A classic loop diuretic, furosemide (10 mg/kg ip), markedly increased renal medullary Po(2) levels from 22.5 to 52.2 mmHg, which was accompanied by a significant reduction of HIF-1alpha transcripts in renal medullary tissue. In in vitro experiments, low Po(2), but not elevated osmolarity, was found to significantly increase HIF-1alpha mRNA in renal medullary interstitial cells and inner medullary collecting duct cells. These results indicate that HIF-1alpha is more abundantly expressed in the renal medulla compared with the renal cortex. Increased abundance of HIF-1alpha mRNA in the renal medulla may represent an adaptive response of renal medullary cells to low Po(2).

Effect of selective inhibition of soluble guanylyl cyclase on the K(Ca) channel activity in coronary artery smooth muscle

Activation of a soluble guanylyl cyclase plays an important role in nitric oxide (NO)-induced vasodilation. Recently, we have reported that NO increases the calcium-activated potassium (K(Ca)) channel activity in vascular smooth muscle cells from coronary arteries. The present study examined the role of the soluble guanylyl cyclase in the control of basal activity of the K(Ca) channels and in mediating NO-induced activation of the K(Ca) channels in vascular smooth muscle cells, using a selective inhibitor of this enzyme, 1H-[1,2,4]oxadiazolo[4,2-alpha]quinoxalin-1-one (ODQ). In the cell-attached patch-clamp mode, addition of ODQ into the bath solution (10 micromol/L) decreased the K(Ca) channel activity by 59% and attenuated activation of the channels induced by the NO donor, deta nonoate, by 70%. ODQ had no effect on 8-bromo-cGMP-induced activation of the K(Ca) channels. Deta nonoate produced a concentration-dependent relaxation of precontracted coronary arteries. When ODQ was added to the bath, the deta nonoate-induced relaxations were inhibited. The IC50 for deta nonoate was decreased by about 25-fold and the maximal effect of deta nonoate was reduced by about 60%. A specific K(Ca) channel inhibitor, iberiotoxin, decreased deta nonoate-induced vasodilation but to a lesser extent than ODQ. However, ODQ was without effect on the vasodilation induced by a prostacyclin analog, iloprost, and by adenosine. These results indicate that a soluble guanylyl cyclase and cGMP play an important role in the control of the K(Ca) channel activity in coronary arterial smooth muscle cells. K(Ca) channel activation participates in the NO-induced vasodilation in coronary circulation.

Effect of ceramide on KCa channel activity and vascular tone in coronary arteries

A sphingomyelin metabolite, ceramide, serves as a second messenger in a variety of mammalian cells. Little is known regarding the production and actions of this novel intracellular signaling lipid molecule in the vasculature. The present study was designed to test the hypothesis that a ceramide-mediated signaling pathway is present in coronary arterial smooth muscle and that ceramide serves as an inhibitor of the large-conductance Ca2+-activated potassium (KCa) channels and mediates vasoconstriction in coronary circulation. We found that C2-ceramide produced a concentration-dependent decrease in KCa channel activity in vascular smooth muscle cells from small bovine coronary arteries. The average channel activity of the KCa channels in cell-attached patches decreased from 0.046+/-0.01 to 0. 008+/-0.001 at a C2-ceramide concentration of 10 micromol/L. In inside-out patches, C2-ceramide (1 micromol/L) reduced the average channel activity of the KCa channels from 0.06+/-0.007 to 0.016+/-0. 004. Dithiothreitol, an inhibitor of acidic sphingomyelinase (1 mmol/L), increased the average channel activity of the KCa channels in cell-attached patches from 0.05+/-0.02 of control to 0.26+/-0.04, a 5-fold increase that was reversed by addition of 1 micromol/L ceramide. Glutathione, an inhibitor of neutral sphingomyelinase, was without effect. C2-ceramide significantly reduced the diameter of isolated perfused small coronary arteries in a concentration-dependent manner. Addition of 1 micromol/L C2-ceramide decreased average arterial diameter by 28%. When 14C-sphingomyelin was incubated with coronary arterial homogenates at pH 7.4 and pH 5. 0, 14C-choline phosphate and ceramide were produced. The conversion rates of 14C-sphingomyelin into 14C-choline phosphate and ceramide were 65.1+/-1.0 fmol/min per milligram protein at pH 7.4 and 114. 6+/-8.3 fmol/min per milligram protein at pH 5.0. We conclude that both acidic and neutral sphingomyelinases are present in the bovine coronary arteries and that ceramide inactivates the KCa channel in arterial smooth muscle cells and hence exerts a tonic vasoconstrictor action in coronary microcirculation.