Refractory potassium repletion. A consequence of magnesium deficiency

Experimental and clinical observations support the view that uncorrected magnesium (Mg) deficiency impairs repletion of cellular potassium (K). This is consistent with the observed close association between K and Mg depletion. Concomitant Mg deficiency in K-depleted patients ranges from 38% to 42%. Refractory K repletion due to unrecognized concurrent Mg deficiency can be clinically perplexing. Refractory K repletion as a consequence of Mg deficiency may be operative in patients with congestive failure, digitalis toxicity, cisplatin therapy, and in patients receiving potent loop diuretics. Therefore, we recommend that: (1) serum Mg be routinely assessed in any patients in whom serum electrolytes are necessary for clinical management and (2) until serum Mg is routinely performed consideration should be given to treating hypokalemic patients with both Mg as well as K to avoid the problem of refractory K repletion due to coexisting Mg deficiency.

p52(PAI-1) and actin expression in butyrate-induced flat revertants of v-ras-transformed rat kidney cells

Flat revertants of v-ras-transformed (KNRK) rat kidney cells, which express elevated levels of p21ras protein, were generated to high efficiencies with sodium butyrate (NaB). Overall protein synthesis in revertants was not different from parental cells, although changes were evident in expression and distribution of specific microfilament-associated cytoskeletal proteins. Quantitative two-dimensional electrophoresis revealed revertant-associated 3-4-fold increases in cytoskeletal deposition of the microfilament-associated proteins gelsolin and vinculin correlating with microfilament reorganization and focal-contact formation respectively. Similar increases in actin content were evident at both the total-cellular- and cytoskeletal-associated-protein levels. In contrast, intermediate-filament family elements (vimentin, lamins) remained unaltered. The only unique protein resolved in flat revertants was p52, a 52 kDa extracellular-matrix-associated protein previously identified as plasminogen-activator inhibitor type 1 (PAI-1). p52(PAI-1) expression was induced early during generation of the revertant phenotype and preceded development of focal-contact structures. NaB-induced p52(PAI-1) synthesis and generation of early morphological reversion in KNRK cells required ongoing RNA synthesis, since exposure to actinomycin D before addition of NaB inhibited both events. p52(PAI-1) induction by NaB was regulated at the level of mRNA abundance; in contrast, actin mRNA levels were the same in parental and revertant cells, suggesting that the increased actin content which typified the revertant phenotype was due to augmented actin microfilament stability.

Myocardial contractility and ischaemia in the isolated perfused rat heart with propofol and thiopentone

The effects of propofol and thiopentone on myocardial contractility and global ischaemia were evaluated using an isolated non-working perfused rat heart preparation. Contractility was assessed using a tension transducer linked to the cardiac apex, and the contractility was expressed as a ratio of the deflection size before and after infusion of the drug. Ischaemia-induced leakage of myocardial proteins and ions (potassium and magnesium) was assessed by comparing the concentrations in the effluent perfusate immediately before and after 60 min of isothermic ischaemia, in the presence of propofol, thiopentone or plain Krebs' buffer solution (control). Mean contractility ratios of 1.15 and 1.3 were obtained with control and propofol groups respectively (NS), but were reduced to 0.5 in the thiopentone group (P less than 0.001). The magnitude of the post-ischaemic leakage of proteins and potassium was similar in each group; however, the post-ischaemic leakage of magnesium was greater in the thiopentone group than in the propofol or control groups. These data suggest that, compared with thiopentone, propofol is not a potent negative inotrope, and that it may cause less disturbance of myocardial magnesium homeostasis during myocardial ischaemia.

p52 induction by cytochalasin D in rat kidney fibroblasts: homologies between p52 and plasminogen activator inhibitor type-1

Normal rat kidney (NRK) fibroblasts respond to the cell shape-modulating chemical agent cytochalasin D (CD) with augmented synthesis of the 52-kDa substrate-associated protein p52. p52 is a complex glycoprotein, existing as 12 different isoforms, which include a 43-kDa "core" protein (p43), four 50-kDa species (p50-0,1,2,3), and at least seven distinct pI variants of the mature 52-kDa protein. A threshold of 2-4 microM CD was found to be necessary to augment p52 deposition into both the secreted protein- and saponin-resistant cytomatrix (SAP) fractions of NRK cells. This concentration of CD was also necessary to initiate significant cell rounding. Augmented p52 production in CD-treated NRK (NRK/CD) cells provided a means to assess the identity of this protein. p52 was found to be identical to rat plasminogen activator inhibitor type-1 (rPAI-1) and to PAI-1-like proteins of other species by comparative immunoprecipitation, 2-D electrophoretic profile, V8 protease digest mapping, and subcellular fractionation criteria. Quantitation of rPAI-1 cytoplasmic mRNA abundance, using the rPAI-1 cDNA probe pSS1-3, revealed an induction of rPAI-1 mRNA in NRK/CD cells which paralleled the increased protein production. CD-augmented p52(rPAI-1) synthesis and SAP deposition was blocked by actinomycin D, implicating a need for RNA synthesis during the period of CD exposure to effect induction. Augmentation of p52 expression in NRK/CD fibroblasts, thus, appears to involve both cell shape-associated metabolic processes and concomitant RNA synthesis.

Human red blood cell insulin-degrading enzyme and rat skeletal muscle insulin protease share antigenic sites and generate identical products from insulin

The mechanisms of cellular insulin degradation remain uncertain. Considerable evidence now exists that the primary cellular insulin-degrading activity is a metallothiol proteinase. Two similar degrading activities have been purified and characterized. Insulin protease has been purified from rat skeletal muscle and insulin-degrading enzyme from human red blood cells. Whereas the two degrading activities share a number of similar properties, significant differences have also been reported; and it is not at all established that they are the same enzyme. To examine this, we have compared antigenic and catalytic properties of the two enzymatic activities. Monoclonal antibodies against the red blood cell enzyme adsorb the skeletal muscle enzyme; and on Western blots, the antibodies react with an identical 110-kDa protein. Immunoaffinity-purified enzymes from both red blood cells and skeletal muscle degrade [125I]iodo(B26)insulin to the same products as seen with purified insulin protease and with intact liver and kidney. Chelator-treated muscle and red blood cell enzymes can be reactivated with either Mn2+ or Ca2+. Thus, insulin-degrading enzyme and insulin protease have similar properties. These results support the hypothesis that these activities reside in the same enzyme.

General practice computing in Scotland

OBJECTIVE

To investigate a method of assessing the extent of routine patient data held on computer by Scottish general practitioners.

DESIGN

An "electronic questionnaire" in the form of an interrogation questionnaire was used to extract a subset of data from practice computers running a standard software package (the general practice administrative system for Scotland, GPASS). The data were retained by each practice and also collected and analysed centrally to produce regional and national data.

SUBJECTS

All 257 general practices in Scotland using GPASS software were sent the electronic questionnaire; data from 154 practices, including 759 general practitioners and covering 1,010,452 patients, were collected.

RESULTS

Ninety three practices had all their patient records on computer; others had selectively entered data on, for example, only those patients receiving repeat prescriptions. The number of computerised patient records per practitioner ranged from 46 to 2373. Altogether 194,261 patients had repeat prescribing data and 204,005 morbidity or clinical data.

CONCLUSION

An electronic questionnaire is a simple and effective way of investigating the information held on practice computers, allowing analysis and feedback of information to practitioners. Development of this system will provide a cumulative information system for Scottish general practitioners.

Hypophosphatemia complicating bronchodilator therapy for acute severe asthma

Hypophosphatemia has been recently highlighted as a reversible cause of respiratory muscle hypocontractility and reduced tissue oxygen extraction in patients with chronic obstructive lung disease and asthma. To define the prevalence and mechanism of hypophosphatemia under these circumstances, we studied phosphate homeostasis in 22 patients with chronic asthma, who had been hospitalized for emergency bronchodilator therapy. Serum phosphate concentration was normal in all patients on presentation, and fell after the initiation of bronchodilator therapy. Twelve patients (54%) developed hypophosphatemia (serum phosphate, less than 0.8 mmol/L). Urinary phosphate level fell in parallel. A negative correlation was observed between serum phosphate and serum theophylline concentrations, and a positive correlation between serum and urinary phosphate concentrations. No correlation was found between serum phosphate and serum albumin or urea concentration. These data indicate that hypophosphatemia is a common metabolic abnormality during the emergency treatment of asthma. The underlying mechanism appears to be drug-induced phosphate flux from the extra-cellular to the intracellular space. We suggest that the serum phosphate level be monitored in patients undergoing emergency treatment of bronchospasm, particularly if a prolonged period of bronchodilator therapy is required or if respiratory muscle fatigue supervenes.

Cytochalasin D-mediated hyperinduction of the substrate-associated 52-kilodalton protein p52 in rat kidney fibroblasts

Regulation of certain differentiated and housekeeping functions in cultured mammalian cells is significantly influenced by cell shape. The shape-modulating agent cytochalasin D (CD) was used, therefore, to elucidate potential cytoarchitectural influences affecting synthesis of a major 52 kDa secreted/substrate-associated protein (p52) of normal rat kidney (NRK) fibroblasts. Biosynthetic labeling experiments indicated that treatment of NRK cells with CD increased, by 10-18-fold, the medium content of an Mr 52,000 protein. Two-dimensional gel electrophoresis and peptide fragment mapping confirmed that the 52 kDa protein produced in abundance as a consequence of CD treatment was identical to p52 constitutively expressed by NRK cells. A lower mw protein (p50; Mr 50,000) was also resolved which, based on pl microheterogeneity, protease fragmentation profile, and sensitivity to tunicamycin, could be identified as a less-glycosylated form of p52. p50 and p52 were both detected in the matrix and medium compartments of NRK and NRK/CD cells. The matrix p52 content of CD-induced and uninduced cells, however, was significantly greater (by 200-500-fold) than the corresponding medium levels. This differential compartmentalization, the time course of p52 accumulation in the matrix of NRK/CD cells compared to its appearance in the medium, and the kinetics of p52 pulse-chase from the matrix collectively indicated that the matrix is the initial site of p52 deposition. Low levels of CD (1 microM) produced extensive disruptions of cellular microfilaments but did not result in an overall cell shape change nor a hyperinduction of p52. Morphologic rounding (seen in 10-100 microM CD) coincided with augmented p52 production. Transition from a flat to a round phenotype in NRK cells, or at least the generation of sufficient microfilament fragmentation to compromise cell-substrate adhesivity, appears to be an essential aspect of CD-mediated p52 hyperinduction.

Ethical issues in clinical research

A variety of ethical issues can arise from clinical trials. Personal biases of the health care professional, socioeconomic constraints of the patient, and lack of collaboration and communication between the nurse and the research team create ethical dilemmas. In resolving these dilemmas, it is the responsibility of the oncology nurse to ensure that the principles of autonomy, beneficence, and justice are preserved.

Cytoarchitectural analysis of epithelial sheets formed in vitro by hepatic tumor cells possessing defined intermediate-sized filament cytoskeletal abnormalities

Established 72/22 rat hepatic tumor cells, which bear well-characterized cytoplasmic abnormalities of intermediate filament (IF) network organization, form monolayer "sheets" of tightly juxtaposed epithelial cells at high culture population densities. The distribution of desmosomal complexes and their affiliated tonofilaments, as well as the regulation of cytokeratin/vimentin IF and actin microfilament contents were assessed during construction of this in vitro "epithelium." 72/22 cells formed desmosomal junctions throughout the length of the cellular perimeter. Compared with low population density cultures, fully confluent sheets of 72/22 cells exhibited a down-regulated cytoskeletal actin content and increased level of cytokeratin synthesis. Despite gross IF cytoarchitectural abnormalities, 72/22 cells normally modulated the content of specific structural elements within both the IF and microfilament networks in response to increasing cell-cell contact. Furthermore, these data support the concept that neither the structural integrity nor the topographic distribution of the desmosome array are dependent on tonofilament anchorage or IF scaffold organization.

Biochemical localization of the transformation-sensitive 52 kDa (p52) protein to the substratum contact regions of cultured rat fibroblasts. Butyrate induction, characterization, and quantification of p52 in v-ras transformed cells

A 52 kDa protein (p52) was identified, using differential extraction and electrophoretic criteria, as a major extracellular and substrate-associated component of normal rat kidney (NRK) fibroblasts. Cells transformed with Kirsten murine sarcoma virus (KNRK cells) did not express p52 constitutively, but were inducible for both p52 production and its substrate association during culture in sodium butyrate (NaB)-supplemented growth medium. Comparative analysis of the relative molecular mass, subcellular distribution, and isoelectric complexity (five variants ranging in pI from 5.4 to 6.2) of the 52 kDa species constitutively and inducibly expressed by NRK and KNRK/NaB cells respectively, indicated that they were, indeed, the same protein. p52 selectively localized to cellular fractions enriched in substrate focal contact sites and associated ventral undersurface components. NaB induction of p52 in KNRK cells occurred before cell spreading; other polar compounds, such as dimethyl sulphoxide, which did not induce KNRK cell spreading, similarly failed to elicit p52 production. p52 accumulated more rapidly in (and was quickly released from) the focal-contact-enriched protein fraction of NRK cells compared with its time course of appearance in the medium. These data collectively suggest that p52 is one of a relatively small number of proteins the synthesis of which is either involved in determination of cell shape or regulated as a consequence of cell-shape changes.