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J D Robinson

Publications and source records attributed to J D Robinson.

At least 73 records · Page 4Linked to original sources
PubMed1986

Cation sites, spermine, and the reaction sequence of the (Na+ + K+)-dependent ATPase.

Spermine, at 0.3 mM, inhibits the K+-nitrophenyl phosphatase activity of a dog kidney (Na+ + K+)-ATPase preparation, increasing the K0.5 for K+, reducing the Km for substrate, and affecting little the inhibition by Na+. These actions can be attributed, in a model of the phosphatase reaction, to parallel decreases in affinity for K+ and Na+ at their cytoplasmically accessible sites. In the (Na+ + K+)-ATPase reaction, spermine increases the K0.5 for Na+ and, to a lesser degree, the K0.5 for K+ as activators. With spermine, the double-reciprocal plots of velocity vs. ATP concentration (in the range 0.3-3 mM), at fixed levels of K+ (from 1 to 10 mM), remain parallel but are rotated clockwise and spread somewhat, reflecting stimulation at low ATP concentrations and inhibition at high ATP but low KCl concentrations. These actions can be attributed, in a steady-state ping-pong model of the ATPase reaction, solely to decreased rates of binding of Na+ and K+ to their sites, with major effects at the cytoplasmically accessible sites for Na+ (acceptance) and K+ (discharge), and with a lesser effect at the extracellularly accessible sites for K+ (acceptance). On these grounds, spermine is a highly specific and potentially valuable reagent for studying the reaction. Furthermore, the model for K+-ATP interactions not only supports a specific reaction sequence (K+ addition, Pi release, ATP addition, K+ release) but also argues against the availability of low-affinity substrate sites except during sharply restricted segments of the reaction sequence, thereby favoring proposals that the low-affinity substrate sites are transformed into high-affinity substrate sites with the E2 to E1 conformational change.

Adenosine Triphosphate↗
PubMed1986

Fluoride and beryllium interact with the (Na + K)-dependent ATPase as analogs of phosphate.

Fluoride irreversibly inhibits the (Na + K)-ATPase, and this inactivation requires divalent cations (Mg2+, Mn2+, or Ca2+), is augmented by K+, but is diminished by Na+ and by ATP. Prior incubation with the aluminum chelator deferoxamine markedly slows inactivation, whereas adding 1 microM AlCl3 speeds it, consistent with AlF-4 being the active species. Prior incubation of the enzyme with vanadate also blocks inactivation by fluoride added subsequently. Fluoride stimulates ouabain binding to the enzyme, and thus the analogy between AlF-4 and both orthophosphate and orthovanadate is reflected not only in the similar dependence on specific ligands for their enzyme interactions and their apparent competition for the same sites, but also in their common ability to promote ouabain binding. Beryllium also irreversibly inhibits the enzyme, and this inactivation again requires divalent cations, is augmented by K+, but is diminished by Na+ and by ATP. Similarly, prior incubation of the enzyme with vanadate blocks inactivation by beryllium added subsequently. Inactivation by beryllium, however, does not require a halide, and, unlike inactivation by fluoride, increases at basic pHs. These observations suggest that beryllium, as beryllium hydroxide complexes, acts as a phosphate analog, similar to AlF-4 and vanadate.

Aluminum↗
PubMed1985

Divalent cations and the phosphatase activity of the (Na + K)-dependent ATPase.

Phosphatase activity of a kidney (Na + K)-ATPase preparation was optimally active with Mg2+ plus K+. Mn2+ was less effective and Ca2+ could not substitute for Mg2+. However, adding Ca2+ with Mg2+ or substituting Mn2+ for Mg2+ activated it appreciably in the absence of added K+, and all three divalent cations decreased apparent affinity for K+. Inhibition by Na+ decreased with higher Mg2+ concentrations, when Ca2+ was added, and when Mn2+ was substituted for Mg2+. Dimethyl sulfoxide, which favors E2 conformations of the enzyme, increased apparent affinity for K+, whereas oligomycin, which favors E1 conformations, decreased it. These observations are interpretable in terms of activation through two cases of cation sites. (i) At divalent cation sites, Mg2+ and Mn2+, favoring (under these conditions) E2 conformations, are effective, whereas Ca2+, favoring E1, is not, and monovalent cations complete. (ii) At monovalent cation sites divalent cations compete with K+, while Na+ at these sites favors E1 conformations. K+ increases the Km for substrate, but both Ca2+ and Mn2+ decrease it, perhaps by competing with K+. On the other hand, phosphatase activity in the presence of Na+ plus K+ is stimulated by dimethyl sulfoxide, by higher concentrations of Mg2+ and Mn2+, but not by adding Ca2+; this is consistent with stimulation occurring through facilitation of an E1 to E2 transition, perhaps an E1-P to E2-P step like that in the (Na + K)-ATPase reaction sequence. However, oligomycin stimulates phosphatase activity with Mg2+ plus Na+ alone or Mg2+ plus low K+: this effect of oligomycin may reflect acceleration, in the absence of adequate K+, of an alternative E2-P to E1 pathway bypassing the monovalent cation-activated steps in the hydrolytic sequence.

Animals↗
PubMed1985

Comparison of eight phenytoin dosing methods in institutionalized patients.

Until now, no evaluation of phenytoin dosing methods has been undertaken in a large group of patients, to our knowledge. The goal of this study was to determine which of eight different dosing methods most accurately predicts a phenytoin steady-state concentration. Seventy-six patients were chosen, retrospectively, from a state-funded institution for the mentally retarded. Eligibility criteria included two or more different doses of phenytoin and corresponding plasma concentrations. Relative predictive performance was determined by comparing results of simple linear regression. Also, relative bias and precision were determined by comparing mean prediction errors, root mean squared errors, and respective 95% confidence intervals. Of the methods requiring one dose-concentration pair, Rambeck's nomogram was the best predictor of phenytoin concentrations. The methods requiring two known doses and plasma concentrations were more accurate. Their predictive performance was equivalent, although use of the Tozer equation might be preferred for its convenience. None of the methods tested were sufficiently precise to substitute for confirmatory serum phenytoin concentrations.

Adolescent↗
PubMed1985

Computer prediction of serum theophylline concentrations in ambulatory patients.

This study assessed the ability of a computer program Simulated Kinetics (SIMKIN) to predict serum theophylline concentrations in ambulatory patients receiving oral theophylline. Data were collected by retrospective review of prospectively obtained data. A total of only 20 measured serum theophylline concentrations could be included in the study, although records of 195 patients were reviewed. An estimated patient compliance of 90-110% was required and was computed using prescription refill information. Predicted serum theophylline concentrations were generated for each patient by entering into the SIMKIN program the characteristics pertinent to theophylline disposition and the patient's theophylline dosing regimen. Actual and SIMKIN-predicted theophylline concentrations were compared by using simple linear regression and by constructing a 95% confidence interval around the mean prediction error and root mean squared error. The ability of SIMKIN to predict therapeutic category, i.e., subtherapeutic, therapeutic, or toxic, was assessed using Fisher's exact test. SIMKIN predictions of individual theophylline concentration were insufficiently accurate to replace confirmatory followup monitoring of actual levels. However, SIMKIN was able to predict the therapeutic category with 70% accuracy. We conclude that SIMKIN may be useful for categorizing a dose regimen of theophylline as therapeutic, but that it is of little use in predicting individual concentrations in outpatients when literature-averaged pharmacokinetic parameters are the sole criteria for prediction, and compliance cannot be accurately assessed.

Adolescent↗
PubMed1985

The pharmacokinetics of glibenclamide: a single dose comparison of four preparations in human volunteers.

The pharmacokinetic properties of two new HB 420 glibenclamide preparations, Semi-Euglucon N 1.75 mg and Daonil N 1.75 mg, and of two older HB 419 glibenclamide preparations, Semi-Euglucon 2.5 mg and Daonil 2.5 mg, were compared in a randomized cross-over study in eight healthy volunteers. The HB 420 glibenclamide preparations induced peak plasma glibenclamide concentrations up to about 90 ng/ml at 1.3 to 1.4 hours after ingestion. Administration of the HB 419 preparations induced significantly lower peak plasma glibenclamide concentrations at 1.8 to 2.3 hours after ingestion. Glibenclamide was absorbed and eliminated more rapidly after administration of both HB 420 preparations than after administration of the HB 419 preparations. The mean elimination half-life of glibenclamide was 1.3 +/- 0.1 hours in the case of both HB 420 preparations and 2.0 to 2.5 +/- 0.2 hours in the case of HB 419 preparations. Although the HB 420 preparations contained lower doses of glibenclamide than the HB 419 preparations, the AUC values after administration of the former were similar to the AUC value obtained after administration of one of the HB 419 preparations, indicating improved absorption of glibenclamide from the newly developed preparations. However, the other HB 419 preparation was associated with the greatest AUC value of all, suggesting that glibenclamide was absorbed from this preparation almost as completely as from the HB 420 preparations.

Adult↗
PubMed1984

Effects of oligomycin and quercetin on the hydrolytic activities of the (Na+ +K+)-dependent ATPase.

Quercetin inhibited a dog kidney (Na+ + K+)-ATPase preparation without affecting Km for ATP or K0.5 for cation activators, attributable to the slowly-reversible nature of its inhibition. Dimethyl sulfoxide, a selector of E2 enzyme conformations, blocked this inhibition, while the K+-phosphatase activity was at least as sensitive to quercetin as the (Na+ + K+)-ATPase activity, all consistent with quercetin favoring E1 conformations of the enzyme. Oligomycin, a rapidly-reversible inhibitor, decreased the Km for ATP and the K0.5 for cation activators, and its inhibition was also diminished by dimethyl sulfoxide. Although oligomycin did not inhibit the K+-phosphatase activity under standard assay conditions, a reaction presumably catalyzed by E2 conformations, its effects are nevertheless accommodated by a quantitative model for that reaction depicting oligomycin as favoring E1 conformations. The model also accounts quantitatively for effects of both dimethyl sulfoxide and oligomycin on Vmax, Km for substrate, and K0.5 for K+, as well as for stimulation of phosphatase activity by both these reagents at low K+ but high Na+ concentrations.

Adenosine Triphosphatases↗
PubMed1984

Effects of pyridoxal phosphate treatment on the (Na + K)-ATPase.

Reaction of a dog kidney (Na + K)-ATPase with pyridoxal phosphate, followed by borohydride reduction, reduced the catalytic activity when measured subsequently. The time course of inactivation did not follow a first-order process, and certain characteristics of the residual enzymatic activity were modified. Moreover, various catalytic activities were diminished differently: Na-ATPase activity was largely spared, K-phosphatase activity was diminished only by half that of the (Na + K)-ATPase, whereas (Na + K)-CTPase and Na-CTPase activities were diminished more. ATP, ADP, CTP, nitrophenyl phosphate, and Pi all protected against inactivation. Increasing salt concentrations increased inactivation, but KCl slowed and NaCl hastened inactivation when compared with choline chloride. Occupancy of certain substrate or cation sites seemed more crucial than selection of conformational states. For the residual (Na + K)-ATPase activity the K0.5 for K+ was lower and the K0.5 for Na+ higher, while the sensitivities to ouabain, oligomycin, and dimethylsulfoxide were diminished; for the residual K-phosphatase activity the K0.5 for K+ was unchanged, the sensitivity to ouabain and oligomycin diminished, but the stimulation by dimethylsulfoxide increased. These properties cannot be wholly accommodated by assuming merely shifts toward either of the two major enzyme conformations.

Adenosine Triphosphatases↗
PubMed1984

The oral contraceptive PPI: its effect on patient knowledge, feelings, and behavior.

The distribution of the PPI by pharmacists is at best controversial. Although most health professionals agree that the patient has a right to receive information about drugs, they disagree on the best way to provide that information. Since the oral contraceptive PPI has been in routine use for approximately 10 years, a large data base exists that can be used to determine not only patient acceptance of the PPI, but also knowledge, feelings, and behavior secondary to the PPI. In this study, 50 women of childbearing age completed a questionnaire, and it was learned that 84 percent had taken or were currently taking oral contraceptives, and 90 percent of those received a PPI; however, only 61 percent of these women read all of it. The women performed poorly on the knowledge exam (mean +/- SD, 44.5 +/- 21.2, range, 0-83 percent); those who read all of the PPI or who were white had higher scores (p less than 0.02 and p less than 0.001, respectively). Thirty-eight percent of the women thought that the PPI information was inadequate, suggesting that it needs to be rewritten and/or supplemented with information from pharmacists. After reading the PPI, 12 percent contacted their pharmacist for additional information. Pharmacists are in a unique position to provide oral contraceptive information that enables women to make informed judgments regarding benefit:risk ratios on a personal basis.

Adult↗
PubMed1984

Pharmacists' views on mandatory patient counseling.

A questionnaire was sent to a randomly selected sample of Florida pharmacists to obtain information on the acceptability of mandatory patient counseling. The results of the questionnaire demonstrated that most Florida pharmacists who responded to the survey do not favor a patient counseling regulation. Factors that correlated with a desire for mandatory counseling include: an institutional practice site; assistant director and staff pharmacist position; and a perceived higher income for the patients served by pharmacists. These data indicated that if the mandatory method is selected to stimulate pharmacist-patient interaction, the interrelated issues of reimbursement, facility changes, technician support, patient profiles, continuing education programs, and pharmacists' attitudes toward regulated practice will need to be addressed.

Attitude of Health Personnel↗
PubMed1984

Comparison of standard and modified enzyme immunoassay of phenytoin.

A modified method for the enzyme immunoassay (EMIT, Syva Company) of phenytoin is presented and compared with the standard method. Serum samples from 14 patients were analyzed for phenytoin content using both methods. All assays were performed by the same individual. Within-day and between-day variations of the modified method were determined. A carry-over study was done to determine if a sample with a high phenytoin concentration might contaminate subsequent samples with lower concentrations or whether samples with low concentrations could dilute subsequent samples with higher concentrations. Within-day and between-day variations of the modified method were 7.5% and 9.9%, respectively. These values are less than the 10% coefficient of variation limit claimed by the manufacturer of the standard method. The carry-over study revealed no significant carry-over with the modified method. An excellent correlation was observed between the values obtained from the two methods. The modified method can reduce assay costs by up to 40%. The modified method was found to provide accuracy and precision equivalent to the standard EMIT method at a substantial cost savings.

Costs and Cost Analysis↗
PubMed1984

How to establish a pharmacokinetics consulting service for ambulatory patients.

Guidelines on establishing a pharmacokinetics consultation service are presented with emphasis on outpatient services. Need for the service must first be demonstrated, using the literature and local data on frequency of serum drug concentration monitoring for particular drugs and patient subgroups. Physician interest in the program must be determined. The pharmacist intervention may be restricted to technical interpretation of serum drug concentration data, or it can include advice based on the patient's disease process, drug effects, and the interaction between the two. In the service described, a patient interview, a chart review, drug analysis, and a written consultation were provided. A flow chart showing movement of the patient through the service was used, and the pharmacist documented the consultation in the patient's medical record, including recommendations for dosage change and follow-up. Cost items to consider in establishing the service include equipment and supplies, space, and personnel. Staff members who are responsible for serum drug analyses must meet state-specific requirements. In estimating revenues, the current number of requests for serum drug concentrations should be doubled and the institution's estimated rate of collection should be used. After the service is established, the cost of a computerized system for pharmacokinetic predictions may be justified by the increased efficiency of such a system.

Cost-Benefit Analysis↗
PubMed1983

A model for the reaction pathways of the K+-dependent phosphatase activity of the (Na+ + K+)-dependent ATPase.

(Na+ + K+)-dependent ATPase preparations from rat brain, dog kidney, and human red blood cells also catalyze a K+ -dependent phosphatase reaction. K+ activation and Na+ inhibition of this reaction are described quantitatively by a model featuring isomerization between E1 and E2 enzyme conformations with activity proportional to E2K concentration: (formula; see text) Differences between the three preparations in K0.5 for K+ activation can then be accounted for by differences in equilibria between E1K and E2K with dissociation constants identical. Similarly, reductions in K0.5 produced by dimethyl sulfoxide are attributable to shifts in equilibria toward E2 conformations. Na+ stimulation of K+ -dependent phosphatase activity of brain and red blood cell preparations, demonstrable with KCl under 1 mM, can be accounted for by including a supplementary pathway proportional to E1Na but dependent also on K+ activation through high-affinity sites. With inside-out red blood cell vesicles, K+ activation in the absence of Na+ is mediated through sites oriented toward the cytoplasm, while in the presence of Na+ high-affinity K+ -sites are oriented extracellularly, as are those of the (Na+ + K+)-dependent ATPase reaction. Dimethyl sulfoxide accentuated Na+ -stimulated K+ -dependent phosphatase activity in all three preparations, attributable to shifts from the E1P to E2P conformation, with the latter bearing the high-affinity, extracellularly oriented K+ -sites of the Na+ -stimulated pathway.

Animals↗
PubMed1983

Kinetic studies on the (Na+ + K+)-dependent ATPase evidence for coexisting sites for Na+, K+ and Mg2+.

Na+-ATPase activity of a dog kidney (Na+ + K+)-ATPase enzyme preparation was inhibited by a high concentration of NaCl (100 mM) in the presence of 30 microM ATP and 50 microM MgCl2, but stimulated by 100 mM NaCl in the presence of 30 microM ATP and 3 mM MgCl2. The K0.5 for the effect of MgCl2 was near 0.5 mM. Treatment of the enzyme with the organic mercurial thimerosal had little effect on Na+ -ATPase activity with 10 mM NaCl but lessened inhibition by 100 mM NaCl in the presence of 50 microM MgCl2. Similar thimerosal treatment reduced (Na+ + K+)-ATPase activity by half but did not appreciably affect the K0.5 for activation by either Na+ or K+, although it reduced inhibition by high Na+ concentrations. These data are interpreted in terms of two classes of extracellularly-available low-affinity sites for Na+: Na+-discharge sites at which Na+-binding can drive E2-P back to E1-P, thereby inhibiting Na+-ATPase activity, and sites activating E2-P hydrolysis and thereby stimulating Na+-ATPase activity, corresponding to the K+-acceptance sites. Since these two classes of sites cannot be identical, the data favor co-existing Na+-discharge and K+-acceptance sites. Mg2+ may stimulate Na+-ATPase activity by favoring E2-P over E1-P, through occupying intracellular sites distinct from the phosphorylation site or Na+-acceptance sites, perhaps at a coexisting low-affinity substrate site. Among other effects, thimerosal treatment appears to stimulate the Na+-ATPase reaction and lessen Na+-inhibition of the (Na+ + K+)-ATPase reaction by increasing the efficacy of Na+ in activating E2-P hydrolysis.

Animals↗