Complex regulation of plasminogen activator inhibitor type-1 (PAI-1) gene expression by serum and substrate adhesion

Expression of plasminogen activator inhibitor type-1 (PAI-1), a member of the serine protease inhibitor (SERPIN) superfamily that functions to negatively regulate the plasmin-based pericellular proteolytic cascade, was induced early after exposure of growth-arrested normal rat kidney (NRK) cells to serum-containing medium. Increased PAI-1 transcription was rapid (evident within 10 min of serum addition) and involved immediate-early response kinetics. [3H]Thymidine autoradiography was used to map the time frame of PAI-1 expression during a synchronous growth cycle. PAI-1 transcript accumulation peaked in mid-G1 phase (approx. 4-6 h post-stimulation) and declined prior to, or concomitant with, the onset of DNA synthetic phase. Serum increased PAI-1 expression in NRK cells in agarose suspension, as well as monolayer, culture; induction in suspended cells (similar to monolayer culture conditions) also occurred in the presence of cyclohexamide or puromycin. The serum-inductive pathway leading to PAI-1 gene activation is thus functional regardless of adhesive conditions or capacity for de novo protein synthesis. The amplitude of induction and maintenance of expression in later stages of G1, however, were subject to adhesive influences. PAI-1 transcript accumulation at 4 and 8 h post-stimulation in newly adherent cells, moreover, was blocked by puromycin, indicating that both immediate-early and secondary mechanisms regulate PAI-1 mRNA levels during progression of NRK cells through an 'activated' G1 growth phase.

An application in cheddar cheese manufacture for a strain of Lactococcus lactis producing a novel broad-spectrum bacteriocin, lacticin 3147

Lactococcus lactis DPC3147, a strain isolated from an Irish kefir grain, produces a bacteriocin with a broad spectrum of inhibition. The bacteriocin produced is heat stable, particularly at a low pH, and inhibits nisin-producing (Nip+) lactococci. On the basis of the observation that the nisin structural gene (nisA) does not hybridize to DPC3147 genomic DNA, the bacteriocin produced was considered novel and designated lacticin 3147. The genetic determinants which encode lacticin 3147 are contained on a 63-kb plasmid, which was conjugally mobilized to a commercial cheese starter, L. lactis subsp. cremoris DPC4268. The resultant transconjugant, DPC4275, both produces and is immune to lacticin 3147. The ability of lacticin 3147-producing lactococci to perform as cheddar cheese starters was subsequently investigated in cheesemaking trials. Bacteriocin-producing starters (which included the transconjugant strain DPC4275) produced acid at rates similar to those of commercial strains. The level of lacticin 3147 produced in cheese remained constant over 6 months of ripening and correlated with a significant reduction in the levels of nonstarter lactic acid bacteria. Such results suggest that these starters provide a means of controlling developing microflora in ripened fermented products.

The role of the renin-angiotensin system in cisplatin nephrotoxicity

The role of the renin-angiotensin system (RAS) in the pathogenesis of cisplatin nephrotoxicity was evaluated in an experimental rat model using a specific, nonpeptide angiotensin II(AII) receptor blocker, losartan. Rats were treated with a single dose of losartan (at 10 mg/kg and 30 mg/kg, i.p.) or saline, 2 h prior to cisplatin administration (5 mg/kg, i.p.). Renal function was assessed 3 and 7 days after cisplatin treatment. A second group of rats received losartan (10 mg/kg, i.p.) or saline, 2 h prior to cisplatin administration (5 mg/kg, i.p.), and losartan (10 mg/kg, i.p.) or saline daily for 6 days after cisplatin treatment. Renal function was assessed on day 7. Neither high- nor low-dose losartan pretreatment prevented development of cisplatin-induced nephrotoxicity. Blood urea nitrogen (BUN) and plasma creatinine values at 7 days were similar to those of animals receiving cisplatin alone (BUN: 17.12 +/- 1.1 and 22.17 +/- 2.2 vs. 20.58 +/- 2.4 mg/dL; creatinine: 1.04 +/- 0.05 and 0.82 +/- 0.09 vs. 0.84 +/- 0.06 mg/dL). A significant reduction in creatinine clearance with cisplatin treatment was seen 3 days after therapy, which was not prevented by pretreatment with losartan (GFR in controls: 2.1 +/- 0.16 mL/min; cisplatin: 0.24 +/- 0.05; cisplatin plus low-dose losartan: 0.05 +/- 0.03 and cisplatin plus high-dose losartan: 0.37 +/- 0.05). All groups of cisplatin-treated rats displayed systemic signs of cisplatin toxicity: reduced food intake and body weight. Rats receiving chronic losartan treatment had more rapid weight gain and lower BUN and plasma creatinine levels on day 7 than rats receiving cisplatin alone (BUN: 24.0 +/- 2.64 vs. 36.4 +/- 0.91 mg/dL; p < 0.05; plasma creatinine: 0.86 +/- 0.06 vs. 1.15 +/- 0.07 mg/dL; p < 0.05). Acute blockade of the AII receptor with losartan does not alter the onset or severity of cisplatin nephrotoxicity. Chronic blockade of the AII receptor may improve the rate of recovery of renal function in cisplatin-treated rats.

The standard electrocardiogram as a screening test for hypertrophic cardiomyopathy

Phenotypic heterogeneity in hypertrophic cardiomyopathy (HC) makes definitive diagnosis difficult, particularly during family screening. We studied the electrocardiogram (ECG) as a potential initial screening test in patients with HC. Using accepted diagnostic criteria, we examined the ECGs and echocardiograms of 159 patients with a confirmed clinical or genetic diagnosis of HC. An abnormal ECG was found in 154 patients (97%) while only 146 (92%) showed an abnormal echocardiogram. Of the former, 9 patients (6%) had normal echocardiograms and had been diagnosed on the basis of identification of a mutation in the beta myosin heavy chain gene (n = 8) or obligate carrier status (n = 1). Only 1 of these 9 patients was under age 20, the time at which hypertrophy is normally expressed on the echocardiogram. The remaining 5 patients (3%) without ECG abnormality consisted of 1 patient with an echocardiogram clearly diagnostic of HC and 4 clinically normal patients (aged 13, 24, 29, and 33 years) with normal echocardiograms who had been diagnosed by mutation identification (n = 3) or obligate carrier status (n = 1). Thus only these latter 4 patients (3%) would not have been diagnosed as having HC based on an abnormal ECG and/or abnormal echocardiogram. Screening relatives for HC by ECG criteria alone detects all those whom an echocardiogram will diagnose. While echocardiography aids in the specificity of HC diagnosis, the ECG, within the context of a family with a proven case of HC, is a more sensitive marker of the disease. It is therefore both a cost-effective and useful tool for screening those to proceed to echocardiography.

Evidence for location of the CFTR in human placental apical membrane vesicles

Ion transport (36Cl uptake) and immunochemical studies were undertaken to detect the cystic fibrosis transmembrane conductance regulator (CFTR) in apical membrane vesicles prepared from human placenta. 36Cl uptake into membrane vesicles was studied in the absence and presence of inwardly directed potassium gradients and valinomycin (Ko = Ki and Ko > Ki, where Ko is potassium concentration outside and Ki is potassium concentration inside the vesicles). The sensitivities of 36Cl uptake to the inhibitors 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), bumetanide, and diphenylamine-2-carboxylate were investigated. Each compound significantly inhibited uptake under both sets of conditions. Additional inhibition of 36Cl uptake was found when the compounds were added together, indicating that they were acting at least partly on different components of the 36Cl uptake. The DIDS- and bumetanide-insensitive component of transport was more selective for Cl than I. These findings suggested that this component may, at least in part, represent Cl transport via CFTR. Addition of adenosine 5'-O-(3-thiotriphosphate) (0.8 mM) led to a decrease in total 36Cl uptake but masked in the overall decrease was an increase in the DIDS- and bumetanide-insensitive component of 36Cl uptake. Western blot analysis of the apical membrane proteins with an antibody specific for a region of human CFTR detected a protein band of approximately 190 kDa. These ion transport and immunochemical studies provide evidence that CFTR is located in human placental apical membrane vesicles.

Protection from cisplatin nephrotoxicity by A68828, an atrial natriuretic peptide

The ability of a 13 amino-acid analog of atrial natriuretic peptide (ANP), A68828, to prevent development of cisplatin toxicity was evaluated in a rat model. ANP (1 microgram/kg/min), A68828 (10 micrograms/kg/min), A68828 (50 micrograms/kg/min), or peptide buffer was given as an intravenous infusion over 1 h beginning 15 min prior to an infusion of 5 mg/kg cisplatin. Animals receiving cisplatin plus peptide buffer vehicle developed predictable renal failure, with mean plasma creatinine and blood urea nitrogen concentrations of 1.09 +/- 0.09 mg/dL and 50.13 +/- 5.96 mg/dL, 72 h after treatment. ANP and A68828 (10 micrograms/kg/min) attenuated the increase in these indices of nephrotoxicity (mean plasma creatinine 0.86 +/- .06 mg/dL and 0.76 +/- 0.11 mg/dL, respectively). Surprisingly, the higher dose of A68828 (50 micrograms/kg/min) did not reduce cisplatin nephrotoxicity (72-h plasma creatinine 1.61 +/- 0.34 mg/dL). These results indicate that a short-term infusion of ANP or the analog A68828 can reduce the severity of cisplatin toxicity. At high doses of A68828 the beneficial effects of treatment may be lost.

Cell-shape-dependent modulation of p52(PAI-1) gene expression involves a secondary response pathway

Expression of the rat p52(PAI-1) gene is positively regulated by agents that influence cellular microfilament organization and/or cell-to-substrate adhesion [e.g. cytochalasin D (CD) and sodium n-butyrate (NaB)] [Higgins, Chaudhari and Ryan (1991) Biochem. J. 273, 651-658; Higgins, Ryan and Providence (1994) J. Cell. Physiol. 159, 187-195]. As shape-responsive genes may be subject to inducer-specific controls, the biochemical mechanisms underlying the shape-dependent pathway of p52(PAI-1) gene regulation were examined in v-ras-transformed rat kidney (KNRK) cells. NaB and/or CD effectively stimulated p52(PAI-1) run-off transcription and augmented de novo p52(PAI-1) mRNA and protein synthesis in KNRK cells; induction at both the mRNA and protein levels was inhibited by actinomycin D. Pretreatment with cycloheximide (CX) markedly attenuated NaB- and/or CD-stimulated p52(PAI-1) expression. CX alone, however, induced low levels of p52(PAI-1) mRNA; increased p52(PAI-1) protein synthesis was evident after release of KNRK cells from CX blockade. Such CX-mediated induction was also sensitive to actinomycin D. Full stimulation of p52(PAI-1) expression in KNRK cells in response to the shape modulators NaB and/or CD involves transcriptional activation of the p52(PAI-1) gene, requires de novo RNA synthesis and occurs through a secondary-response (i.e. protein-synthesis-dependent) pathway.

Induced expression of p52(PAI-1) in normal rat kidney cells by the microfilament-disrupting agent cytochalasin D

In established normal rat kidney (NRK) cells, synthesis of the 52 kDa type-1 inhibitor of plasminogen activator [p52(PAI-1)] is stimulated by the cell shape-modulating fungal metabolite cytochalasin D (CD). Induction paralleled the time course of morphologic change and reflected relatively specific increases in saponin-resistant p52(PAI-1) protein accumulation (approximating ten- to thirty-fold over control) and mRNA abundance (seven- to nine-fold). Augmented p52 (PAI-1) mRNA levels closely correlated with increases in 43 kDa p52(PAI-1) core protein biosynthesis. Sensitivity to tunicamycin indicated that N-linked post-translational modifications to this 43 kDa core species generated the full complement of 50 kDa (intermediate) and 52 kDa (mature) p52(PAI-1) glycosylated isoforms. CD-induced p52(PAI-1) expression occurred efficiently in quiescent NRK cells maintained under serum-free conditions as well as in fully serum-supplemented actively growing cultures. While 8-bromo-cAMP reduced both constitutive and transforming growth factor-beta-induced p52(PAI-1) synthesis by > 50%, no such inhibition was evident in short-term (4 h) CD-stimulated cultures. Long-term (24 h) exposure of NRK/CD cells to 8-bromo-cAMP did result in an approximately 34% reduction in stimulated p52(PAI-1) expression, however, levels expressed by NRK/CD+cAMP populations remained markedly elevated relative to control values. These data suggest the existence of a cell shape-dependent aspect of p52(PAI-1) expression control distinct from both the constitutive and growth factor-mediated pathways of gene regulation.

The nephrotoxicity, cytotoxicity and renal handling of a cisplatin-methionine complex in male Wistar rats

When cisplatin is administered in the form of a cisplatin-methionine substitution complex, high doses of cisplatin can be tolerated with no obvious signs of renal toxicity. We have demonstrated that male Wistar rats receiving a single i.p. dose of cisplatin-methionine at a 1:5 ratio (by weight) did not exhibit cisplatin-induced nephrotoxicity, while cisplatin administered alone at an identical concentration (6 mg/kg) resulted in marked renal toxicity in all animals treated. Using renal cortical slices prepared from untreated rats, we demonstrated that cisplatin, but not cisplatin-methionine, inhibited the accumulation of 14C-tetraethylammonium (TEA). This observation suggests that cisplatin, unlike cisplatin-methionine, is a substrate for the organic base transport system. In addition, cisplatin alone was more cytotoxic to C6 glioma cells in vitro than the cisplatin-methionine complex. Exposure of C6 glioma cells to cisplatin-methionine, however, resulted in a 50%-60% reduction in 3H-thymidine incorporation at cisplatin:methionine ratios up to 1:10. These results indicate that cisplatin-methionine is significantly cytotoxic yet lacks cisplatin-associated renal toxicity and may, therefore, have a role in the treatment of human malignancies.

Amiloride-sensitive sodium uptake into human placental brush border membrane vesicles

Sodium transport into human placental brush border membrane vesicles was examined in the presence of an outwardly directed sodium gradient leading to the formation of an intravesicular negative charge. 22Na entered the vesicles in a time dependent fashion. The activation energy of the uptake process was calculated and was found to be 11.2 kcal/mol, similar to the value of ionic diffusion in free solution. Amiloride inhibited Na uptake in a concentration dependent fashion with an IC50 value of 3.08 microM. Neither ouabain nor bumetanide had an effect on Na uptake at concentrations up to 100 or 1000 microM, respectively. The system presented here indicates Na transport via channels without involvement of the Na-K-ATPase or the Na-K-Cl cotransporter. The system may be useful in investigating Na transport defects in cystic fibrosis.

Mobilization of Ca2+ influx, but not of stored Ca2+, by extracellular ATP in rat submandibular gland acini

To determine its effect on cytosolic Ca2+ levels (Ca2+i) and to assess its role as an autonomic cotransmitter, ATP was added to suspensions of rat pancreatic or submandibular gland acini loaded with fura-2. ATP had no effect on pancreatic acinar Ca2+i at either high (2.5 mM) or low (< 10 nM) extracellular Ca2+ concentrations (Ca2+o). In submandibular acini, ATP had little effect on Ca2+i when Ca2+o was < 10 nM but, with Ca2+o equal to 2.5 mM, ATP increased Ca2+i to a steady-state level 2-4 times the resting level of 50-100 nM. Addition of carbachol or epinephrine further increased Ca2+i. The mean and standard deviation of the ATP4- concentration at half of maximal activity (K0.5 ATP4-) was 33 +/- 7 microM and the Hill coefficient was 1.5 +/- 0.7 (n = 9). The active species is apparently ATP4-, as adding Mg2+ increases the total concentration of ATP needed to elevate Ca2+i. GTP, UTP, ADP and adenosine produced no significant changes in Ca2+i. However, 3'-O-(4-benzoyl)benzoyl ATP (BZATP) increased Ca2+i with a K0.5 BZATP of 2.4 +/- 0.5 microM and a Hill coefficient of 2.8 +/- 0.4 (n = 8). ATP-induced changes in Ca2+i were not due to a generalized increase in acinar-cell permeability and were unaffected by voltage-dependent Ca2+ channel blockers or by the presence of depolarizing concentrations of K+.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracellular ATP prevents the release of stored Ca2+ by autonomic agonists in rat submandibular gland acini

In dose-dependent fashion, extracellular ATP reduces the increase in cytosolic Ca2+ concentration ([Ca2+]o) due to mobilization of cellular Ca2+ stores by both epinephrine [half-maximal inhibitory concentration (IC50) = 35.7 +/- 12.9 microM; Hill coefficient (NH) = -2.0 +/- 0.7, n = 8] and by carbachol (IC50 = 27.0 +/- 7.0 microM, NH = -2.3 +/- 0.7, n = 9). Inhibition is due to ATP4- but does not result from any emptying or inaccessibility of Ca2+ stores, which are readily mobilized by thapsigargin in the presence of ATP4-. Reduction of Ca2+ mobilization is rapid but is not due to direct interference by ATP with the interaction of carbachol or epinephrine with their respective cell surface receptors. A benzoyl derivative of ATP, 3'-O-(4-benzoyl) adenosine 5'-triphosphate (BZATP) is more potent than ATP in reducing [Ca2+]i due to mobilization of stored Ca2+ by either carbachol or epinephrine (IC50 for carbachol = 3.9 +/- 0.4 microM, NH = -3.2 +/- 0.5; IC50 for epinephrine = 3.8 +/- 0.2, NH = -2.6 +/- 0.7, n = 3) but GTP, UTP, ADP, and adenosine do not inhibit mobilization of stored Ca2+ by either carbachol or epinephrine. Neither ATP nor BZATP prevents the influx of extracellular Ca2+ stimulated by carbachol or epinephrine. These results suggest that ATP inhibits Ca2+ mobilization by autonomic neurotransmitters after occupation of P2Z purinoceptors.

Hyperoxic stress elevates p52(PAI-1) mRNA abundance in cultured cells and adult rat pulmonary tissue

Hyperoxic stress alters expression of genes involved in extracellular matrix (ECM) remodeling. To identify novel ECM-associated gene products positively regulated by hyperoxia, rat kidney cells were exposed to 95% O2, and the complement of [35S]methionine-labeled, saponin-resistant, ECM-associated proteins was compared with normoxic controls. O2-stressed cells accumulated significantly greater ECM levels (approximately 3- to 4-fold that of control cells) of a 52-kDa glycoprotein (p52), recently identified as the matrix form of plasminogen activator inhibitor type 1 (PAI-1) (P.J. Higgins, P. Chaudhari, and M.P. Ryan. Biochem. J. 273: 651-658, 1991; P. J. Higgins, M. P. Ryan, R. Zeheb, T. D. Gelehrter, P. Chaudhari. J. Cell. Physiol. 143:321-329, 1990), which peaked at 48 h of exposure. Hyperoxia-associated increases in ECM p52(PAI-1) content reflected parallel elevations in p52(PAI-1) mRNA abundance. Similar results were obtained using secondary cultures of rat pulmonary fibroblasts. This 48-h period of maximal hyperoxia-induced p52(PAI-1) expression in vitro was used to design subsequent in vivo studies. Adult rats were exposed to 99% O2 for 24-50 h, and RNA was extracted from the pulmonary tissue of stressed and control animals. A 5- to 8-fold and 6- to 15-fold increase in lung p52(PAI-1) mRNA content was evident in hyperoxia-treated rats at 24 and 50 h, respectively. All of this increase occurred in the defined 3.2-kb species of rat p52(PAI-1) mRNA. Actin mRNA levels increased three- to sevenfold as a function of hyperoxic stress, whereas catalase and glyceraldehyde-3-phosphate dehydrogenase mRNA abundance was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro mechanisms and models of gentamicin nephrotoxicity

Nephrotoxicity is the dose limiting feature of gentamicin adminstration. The nephrotoxic potential of gentamicin was investigated in primary cultures of rat renal proximal tubular cells and in the established renal epithelial cell lines, LLC-PK(1) cells and MDCK cells. Polyaspartic acids have been reported to ameliorate the nephrotoxicity of gentamicin in vivo. However, these compounds have been reported to exert other toxic side effects. We investigated the role of magnesium-l-aspartate-hydrochloride in nephroprotection against gentamicin in these models of nephrotoxicity. Gentamicin admistration resulted in a reduction in the DNA and protein content of the primary proximal tubular cells and an impaired calcium uptake into these cells. Magnesium-l-aspartate-hydrochloride significantly reduced the extent of [(3)H]gentamicin binding to these cells. Transepithelial resistance determination in the established renal cell lines revealed that gentamicin disrupted intercellular communications, while magnesium-l-aspartate-hydrochloride abolished this gentamicin-induced alteration. The actions of gentamicin were shown to occur prior to any loss of cell viability as assessed by flow cytometry. It is concluded that these systems provide useful models for the investigation of gentamicin nephrotoxicity and that magnesium-l-aspartate-hydrochloride may be useful in ameliorating gentamicin nephrotoxicity in clinical conditions.

Growth state-regulated expression of p52(PAI-1) in normal rat kidney cells

In normal rat kidney (NRK) cells, synthesis of the 52-kDa substrate-associated type 1 inhibitor of plasminogen activator [p52(PAI-1)] is linked to alterations in cell shape and substrate adhesion. Subconfluent NRK cells accumulated significantly more ventral undersurface-associated p52(PAI-1) compared to newly confluent or 1-to 2-day postconfluent cultures, suggesting that p52(PAI-1) expression was also growth state-modulated. Since cytoarchitectural constraints function in cell growth control, changes in p52(PAI-1) synthesis were assessed with respect to defined morphologic events that accompany growth activation of cultured NRK cells. Stimulation of low population density, quiescent NRK cells with 20% serum-containing medium resulted in a rapid increase in matrix p52(PAI-1) protein content (6- and 26-fold after 1 and 5 hr, respectively). Growth activation in response to serum reflected activations in p52(PAI-1) cytoplasmic mRNA abundance, which peaked at 2 hr (125-fold increase) and subsequently declined (100-fold increase) at 5 hr poststimulation. Morphologic analysis indicated that quiescent NRK cells were devoid of transcytoplasmic actin filaments and focal contact-associated vinculin. A marked increase in the fraction of cells that elaborated transcytoplasmic microfilaments and vinculin-containing focal adhesions was evident within 5 min of serum addition. Such cytoarchitectural restructuring preceded p52(PAI-1) induction. Morphologic reorganization and p52(PAI-1) induction occurred prior to progression of cells through the S-phase, indicating they are early events associated with serum stimulation in the NRK cell system. The relevance of p52(PAI-1) induction during this growth state transition is not clear but may influence the established cytoarchitectural changes observed prior to p52(PAI-1) induction by regulating pericellular proteolysis and, thereby, cell-to-substrate adhesion.

Cell-shape-associated transcriptional activation of the p52(PAI-1) gene in rat kidney cells

The microfilament-disrupting agent cytochalasin D (CD) increased (by 10-22-fold) the synthesis de novo and extracellular matrix deposition of plasminogen-activator inhibitor type-1 [p52(PAI-1)] in normal rat kidney (NRK) cells. Transition from a flat to a round phenotype occurred concomitantly with, and may actually precede, p52(PAI-1) induction; both the morphological and p52(PAI-1) responses were dose-dependent. Augmented synthesis became evident between 4 and 5 h of treatment of NRK cells with 100 microM-CD, correlating with a transition from 25 to more than 60% rounded cells. CD-associated increases in p52(PAI-1) mRNA abundance and protein biosynthesis were maximal between 6 and 8 h of continuous CD exposure, declined by 50% thereafter, but remained elevated (by at least 6-21-fold respectively over control values) for 24 h. Changes in p52(PAI-1) mRNA abundance at this 24 h point reflected an approx. 5-fold increase in p52(PAI-1)-gene transcription. These data confirm previous suggestions, based on actinomycin D-sensitivity of the inductive response [Higgins & Ryan (1992) Biochem. J. 284, 433-439], that CD-mediated increases in p52(PAI-1) expression are at least partly due to transcription-level events. Since CD also augments specific cellular responses to growth factors or cytokines, the potential effectiveness of this inducer was evaluated both in the presence and absence of serum growth factors using quiescent NRK cells [a growth state in which p52(PAI-1) is not expressed] as a model system. Induction of p52(PAI-1) synthesis and matrix deposition in CD-stimulated quiescent NRK cells was as efficient under growth-factor-deficient conditions as when CD was added simultaneously with serum. CD alone is thus a complete inducer of p52(PAI-1) expression in NRK cells, an observation that supports the contention that cell shape is an important regulatory element in p52(PAI-1)-gene control.

Factors affecting chloride conductance in apical membrane vesicles from human placenta

Apical membrane vesicles from human term placenta were isolated using a magnesium precipitation technique, and the purity of the vesicles was assessed morphologically using scanning and transmission electron microscopy, and biochemically, using marker enzymes. The vesicles were found to be morphologically intact and significantly enriched in enzymes associated with apical membranes. 36Cl- uptake into these vesicles was studied in the presence of an outwardly directed Cl- gradient. This uptake was found to be time dependent, with an initial rapid uptake tending to peak between 10 and 20 min and thereafter decline. Uptake was found to be voltage dependent since 5 microM valinomycin caused a decrease in uptake. The effects of N-phenylanthranilic acid (NPA) and 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) and bumetanide on the initial rate of Cl- were examined in the presence and absence of 5 microM valinomycin. NPA and DIDS inhibited isotope uptake strongly with IC50 values of 0.83 +/- 0.35 microM and 3.43 +/- 0.37 microM, respectively, in the absence of valinomycin. Although valinomycin reduced 36Cl- uptake by about 80% when added before the isotope, DIDS reduced the uptake which remained in a concentration-dependent fashion with an IC50 of 5.6 +/- 2.1 microM. Under these conditions, NPA was without effect at concentrations below 100 microM. Bumetanide was without effect at the concentrations used in the absence of valinomycin. However, following valinomycin pretreatment, bumetanide reduced 36Cl- uptake significantly at 100 microM concentration. Vesicle diameter, as assessed by flow cytometry, did not change under the conditions employed. The effects of some fatty acids were also investigated. Arachidonic acid and linoleic acid inhibited Cl- uptake with IC50 values of 37.6 +/- 14.9 microM and 4.59 +/- 0.51 microM, respectively. Arachidonyl alcohol and elaidic acid were found to be without effect. These studies show that human placental brush border membrane vesicles possess a chloride conductance channel, the activity of which can be measured in the presence of an outwardly directed Cl- gradient and this channel is sensitive to Cl- channel inhibitors, especially N-phenylanthranilic acid, and can be inhibited by unsaturated fatty acids such as arachidonic acid and linoleic acid.

Changes of cytosolic Ca2+ interfere with measurements of cytosolic Mg2+ using mag-fura-2

In rat pancreatic and submandibular gland acini during exposure to carbachol, changes in the fluorescence emission intensity ratio (R) of acini loaded with mag-fura-2 resemble changes in cytosolic Ca2+ concentration (Ca2+i) in acini loaded with fura-2. Furthermore, changes of R depend on the presence of extracellular Ca2+ (Ca2+o) but are much less influenced by changes in extracellular Mg2+ (Mg2+o). To evaluate interference with measurement of cytosolic Mg2+ (Mg2+i) by changes in Ca2+i, we determined the dissociation constant (Kd) and Hill coefficient (NH) of the Ca(2+)-mag-fura-2 and Mg(2+)-mag-fura-2 complexes in standard solutions, in intact acini after loading with the acetoxymethyl ester of mag-fura-2 (mag-fura-2/AM), and in lysates derived from acini loaded with mag-fura-2/AM. The Kd of the Ca(2+)-mag-fura-2 complex in acini (determined with ionomycin) was 20.49 +/- 5.20 microM, and NH was 1.44 +/- 0.16 (n = 24). Kd of the Mg(2+)-mag-fura-2 complex in acini was 2.25 +/- 0.98 mM, and NH was 1.20 +/- 0.20 (n = 25). Mean Kd values were slightly lower in acinar lysates and in solutions of standard mag-fura-2. In acini from either gland, 1,2-bis(2-aminophenoxy)ethan-N,N,N',N'-tetraacetic acid (BAPTA) suppressed carbachol-induced Ca2+i transients. The R value in stimulated acini loaded with BAPTA and mag-fura-2 increased slightly when Mg2+o was increased from less than 10 nM to 1.2 mM, suggesting that Mg2+ influx contributes to the maintenance of Mg2+i during exposure to carbachol. Under these conditions, pancreatic acinar Mg2+i is 0.53 +/- 0.14 mM (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of the 52 kDa cytoskeletal-like protein of cytochalasin D-stimulated normal rat kidney (NRK/CD) cells as substrate-associated glycoprotein p52 [plasminogen-activator inhibitor type-1 (PAI-1)]. Expression of p52 (PAI-1) in NRK/CD cells is regulated at the level of mRNA abundance

Cell shape profoundly affects cellular metabolic activity, protein and nucleic acid synthesis, and cytoskeletal organization. To examine the influence of cell shape on protein expression, normal rat kidney (NRK) cells were exposed to the microfilament-disrupting drug cytochalasin D (CD), labelled with [35S]methionine, and newly synthesized cellular and cytoskeletal proteins examined by two-dimensional gel electrophoresis. CD produced dramatic changes in cell shape (from a flat to round phenotype) with concomitant 3-7-fold increases in the cellular content and cytoskeletal deposition of the microfilament-associated proteins actin, alpha-actinin, and tropomyosin isoform 1. Augmented actin protein content in NRK/CD cells was paralleled by a corresponding increase in actin mRNA abundance and was inhibited by prior addition of actinomycin D. A detergent-insoluble protein of 52 kDa was also detected at high levels in the cytoskeletal fraction of NRK/CD cells. Two-dimensional electrophoretic mapping of total cellular and cytoskeletal proteins revealed this 52 kDa protein to be the previously described glycoprotein p52 [Higgins & Ryan (1989) Biochem. J. 257, 173-182]. By using electrophoretic and immunochemical criteria, p52 was identified as plasminogen-activator inhibitor type-1 (PAI-1). Like actin, CD-induced p52(PAI-1) synthesis, cellular content, and partitioning to the detergent-insoluble cytoskeletal compartment reflected a corresponding increase in p52(PAI-1) mRNA. Such induction was similarly inhibited by actinomycin D. p52(PAI-1) expression in the NRK-cell system is thus responsive to CD-mediated shape changes and requires ongoing RNA synthesis for its induction. Differential extraction of detached cell bodies and the substrate-adherent 'remnant' fraction of NRK/CD cultures, furthermore, indicated that p52(PAI-1) was not an intrinsic internal cytoskeletal element but, rather, selectively localized to the extracellular residue. p52(PAI-1) retained its detergent-insoluble characteristics even in this isolated 'remnant' fraction, where it was also the predominant protein species resolved.