Enhancement of Quasistationary Shocks and Heating via Temporal Staging in a Magnetized Laser-Plasma Jet.

We investigate the formation of a laser-produced magnetized jet under conditions of a varying mass ejection rate and a varying divergence of the ejected plasma flow. This is done by irradiating a solid target placed in a 20 T magnetic field with, first, a collinear precursor laser pulse (10^{12} W/cm^{2}) and, then, a main pulse (10^{13} W/cm^{2}) arriving 9-19 ns later. Varying the time delay between the two pulses is found to control the divergence of the expanding plasma, which is shown to increase the strength of and heating in the conical shock that is responsible for jet collimation. These results show that plasma collimation due to shocks against a strong magnetic field can lead to stable, astrophysically relevant jets that are sustained over time scales 100 times the laser pulse duration (i.e., >70 ns), even in the case of strong variability at the source.

Improved Measurement of the π→eν Branching Ratio.

A new measurement of the branching ratio R_{e/µ}=Γ(π^{+}→e^{+}ν+π^{+}→e^{+}νγ)/Γ(π^{+}→µ^{+}ν+π^{+}→µ^{+}νγ) resulted in R_{e/µ}^{exp}=[1.2344±0.0023(stat)±0.0019(syst)]×10^{-4}. This is in agreement with the standard model prediction and improves the test of electron-muon universality to the level of 0.1%.

Partial purification of a water-soluble liver protein that regulates adenylate cyclase activity (basal, hormone- and cholera-toxin-activated) and cholera-toxin-catalyzed ADP-ribosylation of the membrane G protein.

We have found in water-soluble extracts of rat liver (and RL-PR-C cloned rat hepatocytes), prepared in the absence of detergent, a factor that markedly enhances basal, isoproterenol and cholera toxin activation of adenylate cyclase of rigorously washed hepatocyte membranes, in the absence of added GTP. The factor, which has characteristics of a protein with an Mr of approx. 35000, has been fractionated from crude cytosol by gel filtration, and then further purified over 50-fold by sequential ion-exchange chromatography. The site of action of the protein appears to be at the level of the guanine nucleotide regulatory (G) protein of the plasma membrane adenylate cyclase complex, as the factor, cooperatively with GTP, also permitted cholera toxin to ADP-ribosylate (from 32P-labeled NAD) two integral membrane proteins that migrated on SDS-polyacrylamide gel electrophoresis gels with the mobilities (Mr approx. 46 000 and 48 000) generally observed for the guanine nucleotide regulator protein subunits. In this system, isoproterenol did not stimulate ADP-ribosylation, in either the presence or absence of the liver protein factor.

Hormone receptors. 7. Characteristics of insulin receptors in a new line of cloned neonatal rat hepatocytes.

1. A new line of cloned, differentiated rat hepatocytes (RL-PR-C) was evaluated for its usefulness as an in vitro system for studying the regulation of the insulin receptor. 2. Insulin rapidly reversibly and specifically bound to RL-PR-C hepatocytes. Binding of tracer 125I-labeled insulin, which was competitively inhibited by native insulin as well as by proinsulin and analogs of insulin and proinsulin in proportion to their biological activity, was not influenced by glucagon, corticotropin, or human growth hormone. Anti-insulin receptor serum from a patient with Acanthosis Nigricans Type B competed with 125I-labeled insulin for binding to cell surface sites. 3. Trypsinization destroyed insulin binding sites, but these were restored by incubation under growth conditions; a 75% restoration of binding sites was achieved by one cell population doubling. 4. RL-PR-C hepatocytes responded to insulin binding by an increase in glycogen synthesis from glucose. The insulin effect was maximal at 85 nM, but was detectable at lower, more physiological, concentrations. 5. Chronic exposure (for at least 3h) of hepatocytes to insulin (10(-10)--(10(-8) M) reduced by up to 60% the number of binding sites for insulin (down-regulation). Down-regulation was prevented by cycloheximide at concentration (10 micron) sufficient to inhibit markedly protein synthesis from tracer isoleucine. Recovery from down-regulation induced by native insulin at 10(-7 M or lower concentrations was complete by 18 h under growth conditions. 6. Although RL-PR-C hepatocytes spontaneously transform after about 90 population doublings, no significant differences between normal and transformed cells were observed in insulin binding characteristics and in interaction of cells with anti-insulin receptor serum. However, transformed cells exhibited a substantially reduced (maximum of 20%) down-regulation response to insulin. 7. RL-PR-C rat hepatocytes appear, for these reasons, to be a useful model system for studying the regulation of the insulin receptor.

Regulatory states of adenylate cyclase in RL-PR-C cloned rat hepatocytes.

The adenylate cyclase of cloned differentiated rat hepatocytes (RL-PR-C) is regulated by cholera toxin, guanine nucleotides and fluoride. The activation of hepatic adenylate cyclase by cholera toxin was additive with that by GTP and synergistic with that by epinephrine. In contrast, when membranes were exposed to cholera toxin in the presence of Gpp(NH)p or fluoride, the response was the same as to these agents in the absence of cholera toxin. Cholera toxin-activated membranes were responsiveness only to epinephrine and GTP, while fluoride-activated membranes responded somewhat to all other agents, and Gpp(NH)p-activated membranes responded to no other agents. These data suggest that responsiveness of hepatic adenylate cyclase to cholera toxin, fluoride and Gpp(NH)p cannot be expressed simultaneously. A model is presented to explain these observations which invokes multiple states of adenylate cyclase, each being sensitive to, or brought about by, a different regulatory agent.

Endogenous and cholera toxin-catalyzed ADP-ribosylation of a plasma membrane protein by RL-PR-C cloned rat hepatocytes.

Cholera toxin catalyzed the ADP-ribosylation of a single plasma membrane protein (Mr 55 000) of both RL-PR-C rat hepatocytes and purified rat liver plasma membranes. Labeling of this protein from nicotinamide [2,8-3H]adenine dinucleotide was competitively inhibited by free arginine, but by no other amino acid tested, including lysine. The same protein was ADP-ribosylated from NAD+ endogenously, i.e., in the absence of toxin. This process was, however, not competitively inhibited by added arginine nor by any other amino acid tested lysine. Free ADP-ribose, even in 50-fold molar excess over the nicotinamide [2,8-3H]adenine dinucleotide substrate, did not reduce (by isotope dilution) the endogenous or cholera toxin-catalyzed labeling of the 55 000 dalton membrane protein. It is likely, therefore, that hepatocyte plasma membranes contain an ADP-ribosyltransferase, with a mechanism similar to that of the A subunit of cholera toxin, in that both transfer ADP-ribose to the same membrane protein and in that neither apparently produce free ADP-ribose as an intermediate. It is also clear that the acceptor residue in the 55 000 dalton protein is different for each process. Cholera toxin-catalyzed and endogenous transfer of ADP-ribose to the hepatocyte plasma membrane protein, in contrast to a pigeon erythrocyte system, required no cytosolic factors. The results indicate that ADP-ribosylation in cloned differentiated rat hepatocytes differs from that in pigeon erythrocytes in that the acceptor protein is larger (55 000 compared to 42 000 daltons), cytosolic factors are not required and transfer of ADP-ribose to the acceptor protein occurs endogenously.

On the mechanism of isoproterenol-induced desensitization of adenylate cyclase in cultured differentiated hepatocytes.

The adenylate cyclase of cultured differentiated RL-PR-C hepatocytes is desensitized to 1-isoproterenol by exposure to this beta-agonist. Virtually complete desensitization occurred by 60 min (intact cells) or 30 min (isolated plasma membranes). Isoproterenol was maximally effective at 10 micrometers, although substantial desensitization occurred at isoproterenol concentrations as low as 10 nM. Protein synthesis was not required for desensitization. Recovery from desensitization under tissue culture conditions was only 25% complete by 24 h. Maximum desensitization was accompanied by only a modest 35% decrease in binding sites (as determined by binding assays with [3H]dihydroalprenolol), with no change in binding affinity. Adenylate cyclase desensitized to 1-isoproterenol responded normally to guanine nucleotides and to fluoride, suggesting that the regulatory and catalytic proteins were not the sites of the desensitization "defect'. Using N-ethylmaleiimide to inactive the regulatory and catalytic proteins, and dicyclohexylcarbodiimide to inactivate the beta-adrenergic receptor, of intact hepatocytes, various heterologous cell fusion hybrids were produced, and their adenylate cyclases tested for responsiveness to 1-isoproterenol; only hybrids containing "desensitized' receptor failed to respond to isoproterenol. These results suggest that the mechanism of desensitization to isoproterenol involves only the receptor component of the receptor-regulatory protein(s)-adenylate cyclase complex, and that the receptors are reduced in number and/or ability to interact with the regulatory protein as a result of the desensitization process.

Interaction of guanine nucleotides with adenylate cyclase in normal and spontaneously transformed RL-RP-C cloned rat hepatocytes.

Spontaneous transformation of RL-PR-C hepatocytes leads to alterations in the adenylate cyclase complex which include a lower than normal basal level of activity, a loss of sensitivity to exogenous GTP, and a decreased sensitivity to isoproterenol. Both normal and transformed membranes possess substantial GTPase activity. Treatment of transformed hepatocyte membranes with either isoproterenol plus GMP or with cholera toxin, under conditions that displace tightly bound GDP, restored the GTP effect on adenylate cyclase, and eliminated the lag in the activation by guanyl-5'-yl-imidodiphosphate. Such pretreatment also enhanced guanine nucleotide effects on the adenylate cyclase of normal hepatocytes. These results are explainable on the basis that transformation increases adenylate cyclase-associated GTPase activity, and increases occupancy of nucleotide regulatory sites by inactive or inhibitory guanine nucleotides, e.g., GDP. Seemingly, both catecholamines and cholera toxin promote an exchange reaction at the regulatory sites, resulting in clearance of these sites of inhibitory nucleotides.

Hormone receptors: VI. On the nature of the binding of glucagon and insulin to human circulating mononuclear leukocytes.

Several characteristics of the binding of insulin and glucagon to human circulating mononuclear leukocytes have been studied. Functional analysis (latex bead ingestion) revealed that cell mixtures, as prepared according to Boyum and used generally in studies of insulin resistance in humans, consist of 20-29% phagocytic monocytes, with the remainder being lymphocytes. Partial separation of monocytes from lymphocytes on columns of Sephadex G-10, followed by correlation of insulin binding with cell type, confirms that the monocyte is the binding species. Insulin influenced neither glucose uptake nor the further conversion of glucose to lipids and CO2 by the leukocytes. The transport of alpha-aminoisobutyrate, a nonmetabolizable amino acid, into these cells was also unaffected by insulin. Monocyte/lymphocyte mixtures specifically bound glucagon and prostaglandin E1. At physiological concentrations of these hormones, steady states were reached in 15 min and 45 min, respectively. In contrast to the 8-10-fold increases in cellular cyclic AMP produced by prostaglandins, the effect of glucagon was very small but apparently real. Under appropriate preincubation conditions, sodium azide and iodoacetamide inhibited phagocytosis and insulin binding in parallel. The binding of glucagon was unaffected by these agents. Although both antimycin A and actinomycin D inhibited phagocytosis of the monocytes, only the former inhibited insulin binding; there was only a slight effect on glucagon binding. We would conclude that the binding of insulin to human circulating monocytes, although reflective of insulin resistance in diabetes mellitus and obesity, may not be to traditional receptors. In contrast, the binding of glucagon to lymphocyte/monocyte mixtures may be to function-linked receptors.

Erythema multiforme after use of topical sulfacetamide.

An 8-year-old boy developed erythema multiforme major after topical administration of sodium sulfacetamide for conjunctivitis. He had received systemic treatment with trimethoprim-sulfamethoxazole four months previously without evidence of drug allergy. There was no history of recent exposure to other drugs or evidence of herpes simplex or Mycoplasma infection. After 12 days of treatment with erythromycin ointment, 1% prednisolone eyedrops, systemic prednisone, and intravenous nafcillin, the patient's condition improved dramatically. A slit-lamp examination showed only superficial punctate keratitis. Two months later his visual acuity had improved from 20/200 bilaterally to R.E.: 20/40 and L.E.: 20/30.

Intraocular pressure trends after supranormal pressurization to aid closure of sutureless cataract wounds.

PURPOSE: To measure intraocular pressure (IOP) immediately and 25 minutes after small sutureless cataract surgery to estimate the duration of any elevation and to evaluate the relationship between supranormal pressurization and an elevated IOP 24 hours postoperatively. SETTING: Routine outpatient cataract surgery at a tertiary referral center. METHODS: Thirty-six consecutive eyes that had uneventful phacoemulsification cataract extraction were studied in a prospective fashion. Supranormal pressurization was attempted in all cases. Surgery was performed through a 3.5 mm scleral wound. RESULTS: Mean IOP dropped from 38.8 mm Hg +/- 11.4 (SD) to 19.8 +/- 5.3 mm Hg 25 minutes after the surgery (P < .0001). A subgroup of patients (n = 6) whose IOP was greater than 24 mm Hg 24 hours postoperatively had a pressure drop from 36.8 +/- 12.3 mm Hg to 23.2 +/- 6.2 mm Hg 25 minutes postoperatively (P = .051). In this subgroup, the mean 24 hour IOP then rose to 30.8 +/- 5.2 mm Hg (P = .043). Another subgroup of patients (n = 7) whose IOP was greater than 24 mm Hg at 25 minutes had a pressure drop from 46.3 +/- 8.5 mm Hg to 27.9 +/- 2.4 mm Hg (P = .0014), falling to 21.7 +/- 6.6 mm Hg at 24 hours (P = .018). CONCLUSION: These findings demonstrate the rapid decline of IOP after supranormal pressurization at the conclusion of cataract surgery. In addition, supranormal pressurization did not seem to contribute to IOP elevation at 24 hours.

Beyond managed care.

Even as the federal government tries to prop up Medicare managed care, HMOs continue to pull out of the program. But a Centers for Medicare & Medicaid Services demonstration project aims to show that one concept of managed care can keep chronically ill patients healthier and lower overall costs. The concept, coordinated care, blends case management and disease management, giving patients the resources to manage their own care more actively. But, please, just don't call it managed care.

Foundations. Show us the money.

Sales of hospitals to for-profit chains have spawned nearly 100 new community foundations. Consumers and state officials increasingly want to know: How will these new charities spend their funds.

Capital: who's got it? How to get it!

Cruel. Fickle. Demanding. While hospitals and HMOs face tougher scrutiny by credit-rating agencies, Wall Street has slowed the flow of capital to practice management and assisted-living start-ups. Meanwhile, some investor-owned hospitals now emphasize debt over equity. In this special report, we examine the capital markets sector by sector.

Accident scenes.

Many hospital errors--including some of the most serious--never come to the attention of executives. A behind-the-scenes study shows how mixed incentives and communication snafus mask patterns of errors.

Unhappy landings. Health care feels the fallout from Washington's 1997 balanced budget.

Health care is already feeling the fallout from the 1997 balanced budget pact. And the accord's $100 billion in Medicare cuts, spread over five years, are only beginning to take effect. H&HN looks at two especially hard-hit sectors: home health agencies and rural hospitals.

Rough crossings.

CEOs change jobs all the time, but only a handful make the jump from not-for-profit to for-profit hospital or vice versa. Some thrive in the new setting. Others crash. Personality makes the difference.

Size does matter.

Hospital mergers, like Godzilla's comeback movie, promise that bulk means marketplace brawn. Yet as the dust settles, the payoff isn't always so clear. Promised efficiencies from merging duplicated programs--even shutting down entire hospitals--often fail to materialize. In fact, cutting the deal may turn out to be the easy part.

The redistricting of Columbia.

Thomas Frist worked up a familiar formula for ailing Columbia/HCA, opting to spin off one-third of its hospitals. The change promises Columbia and its offspring more capital and management scrutiny, but the recovery isn't complete.