Diabetes mellitus, inflammation, obesity: proposed treatment pathways for current and future therapies

OBJECTIVE

To review the pathophysiology, pharmacology, and current or future therapies under study for use in treating diabetes mellitus, inflammation associated with diabetes mellitus, and/or obesity related to diabetes mellitus, through 1 of 4 investigational pathways: adiponectin, ghrelin, resveratrol, or leptin.

DATA SOURCES

A literature search using MEDLINE (1966-December 12, 2009), PubMed (1950-December 12, 2009), Science Direct (1994-December 12, 2009), and International Pharmaceutical Abstracts (1970-December 12, 2009) was performed using the terms adiponectin, ghrelin, resveratrol, leptin, inflammation, obesity, and diabetes mellitus. English-language, original research, and review articles were examined, and citations from these articles were assessed as well.

STUDY SELECTION AND DATA EXTRACTION

Clinical studies and in vitro studies were included in addition to any Phase 1, 2, or 3 clinical trials.

DATA SYNTHESIS

Mechanistic pathways regarding adiponectin, ghrelin, resveratrol, and leptin are of interest as future treatment options for diabetes mellitus. Each of these pathways has produced significant in vitro and in vivo clinical data warranting further research as a possible treatment pathway for diabetes-related inflammation and/or obesity reduction. While research is still underway to determine the exact effects these pathways have on metabolic function, current data suggest that each of these compounds may be of interest for future therapies.

CONCLUSIONS

While several pathways under investigation may offer additional benefits in the treatment of diabetes mellitus and associated impairments, further investigation is necessary for both investigational and approved therapies to ensure that the impact in new pathways does not increase risks to patient safety and outcomes.

Disposition of [s]-heparin in the rat

[(35)S]-Heparin is rapidly taken up by tissues after intraperitoneal injection andrapidly degraded. Skin, aorta and lung showed an especially high affinity for[(35)S]-heparin. In these organs, as well as in adrenal gland, stomach, heart and brain,the isotope was found preponderantly as dialysable metabolite(s) of heparin. Another group of tissues (large intestine, fat, kidney and liver) was characterized by a smaller proportion of dialysable material. Tissues that showed a high affinity for exogenous heparin appeared to catabolize it rapidly. It is also noted that some of the radioactive material present in tissues after the injection of [(35)S]-heparin could come from the uptake of [(35)S]-sulphate resulting from the degradation of [(35)S]-heparin. The incorporation of [(35)S]-sulphate into the sulphomucopolysaccharides of some tissues is recorded.

Blood levels of flupenthixol in patients with acute and chronic schizophrenia

Plasma levels of flupenthixol were estimated by three methods in 30 patients with acute schizophrenia and 29 patients with chronic schizophrenia. These levels were related to clinical response, anterior pituitary hormone secretion, platelet monoamine oxidase activity, the effects of the concurrent administration of anticholinergic drugs, and body weight. No clearcut relationships between plasma flupenthixol levels and any of these variables were demonstrated. The practical clinical value of the estimation of plasma flupenthixol is limited at the present time.

The DRD2 TaqI-B polymorphism and its relationship to smoking abstinence and withdrawal symptoms

The dopamine receptor D2 (DRD2) gene has polymorphisms that have been linked to regulation of the dopamine system and to an increased prevalence of smoking. The present study examined the relationship of the DRD2 TaqI-A and -B polymorphisms with short-term clinical outcome (abstinence and withdrawal symptoms), collected from daily (14 pre-quit and 42 post-quit) diary data among smokers (n=116) treated with the nicotine patch plus either venlafaxine or placebo. The results showed that B1/B1 or B1/B2 smokers were slightly less likely to be abstinent on a given day than those homozygous for the TaqI-B2 allele. Significant DRD2 TaqI-B x time interactions were found for several of the withdrawal scales, indicating that those smokers with the B1/B1 or B1/B2 genotypes tended to report more symptoms over time compared to those with the B2/B2 genotype. No interactions or main effects were found for the DRD2 TaqI-A polymorphism. The findings demonstrate that smokers homozygous for the TaqI-B2 allele experience progressive improvement in self-reported withdrawal symptoms while smokers with the TaqI-B1 allele showing little change.

Healthcare providers' sun-protection promotion and at-risk clients' skin-cancer-prevention outcomes

BACKGROUND

This study aims to determine whether healthcare providers' (HCPs') communication dealing with sun-protection (i.e., counseling) is associated with clients' skin-cancer-related prevention practices, detection self-efficacy, and knowledge.

METHODS

Secondary analysis of two surveys of 1,469 randomly sampled farmers and soccer participants from southeast and coastal Georgia.

RESULTS

Farmers and soccer participants who report ever having been counseled by a HCP about how to protect their skin from the sun report being more likely to wear sunscreen (P < 0.05), get clinical exams of their skin (P < 0.001), be certain that they can recognize unhealthy changes in their skin (P < 0.001), be certain that they know how to perform a skin exam (P < 0.001), and be knowledgeable about skin cancer prevention (P < 0.05 and P < 0.001, respectively); soccer participants are additionally more likely to wear protective headgear (P < 0.05) and perform monthly self-exams of their skin (P < 0.001). All analyses incorporated three control variables: participants' prior history of skin cancer, age, and non-HCP-derived skin-cancer awareness.

CONCLUSIONS

Findings suggest that HCPs' counseling can positively shape skin-cancer-related prevention practices, detection self-efficacy, and knowledge. Additional research is needed on HCPs' actual communication about skin cancer and sun protection and its influence on client outcomes.

Closing medical encounters: two physician practices and their implications for the expression of patients' unstated concerns

When patients visit primary-care physicians, they frequently have more than one concern. Patients' first concerns are solicited by physicians at the beginnings of encounters. A challenge to health care is how to get patients' additional concerns raised as topics of discussion. If patients' additional concerns are addressed, it tends to occur at the end of encounters. Using the methodology of conversation analysis, this article identifies and describes the interactional organization of two physician-initiated communication practices that are used to negotiate the closure of the business of encounters and a transition into the activity of closing encounters themselves. These practices have different implications for the topicalization of patients' additional concerns.

The time course of emotional and attentional modulation of the startle eyeblink reflex during imagery

Two studies were conducted to examine the time course of attentional and emotional processing using the startle eyeblink reflex. Forty-eight participants listened to a series of 1500-ms tones that occurred every 6 s. The tones signaled participants to generate emotional images that were positive or negative in valence and high or low in arousal. Auditory startle probes occurred 120 ms, 1400 ms, or 4000 ms after tone onset. Startle inhibition was seen 120 ms after tone onset and startle facilitation was found at 1400 ms, compared to startles elicited 4000 ms after tone onset. Startle inhibition was greater at 120 ms when the tone signaled imagery, indicating an attentional effect. A second experiment found that this effect was not caused by the comparative rarity of the tones signaling imagery. Startle magnitude was also smaller at 1400 ms when the tone signaled imagery compared to no-imagery tones. The type of imagery did not modulate the startle response 120 ms after tone onset, but negative valence imagery enhanced startle magnitude at 1400 ms and 4000 ms after tone onset, and high arousal also enhanced startle magnitude at 4000 ms. Thus, attention and emotion followed different time courses in affecting the startle reflex response during imagery.

Women's health problems in soap operas: a content analysis

A content analysis of women's health problems in network daytime serials is reported. Results indicate a preponderance of such problems as substance abuse, falls resulting in death or injury, comas or unconsciousness, mental health concerns (most notably represented by amnesia and multiple personality), concerns about AIDS, automobile accidents, being drugged, fainting, pregnancy problems, and violent acts resulting in harm. Such concerns as breast and cervical cancer and heart disease are less frequently portrayed.

Experimental Characterization of the Higher Vibrationally Excited States of HCO(+): Determination of omega(2), x(22), g(22), and B(030)

Analyses of high Rydberg series of HCO converging to the (030) vibrational state of the cation establish rovibrational state-detailed thresholds for HCO(+). UV-visible laser double resonance isolates series for assignment. Strongly vertical Rydberg-Rydberg transitions from photoselected N' = 0 and N' = 2 rotational levels of the Sigma(-) Renner-Teller vibronic component of the 3ppi (2)Pi (030) complex define individual series converging to rotational levels, N(+) = 1 through 5 and 3 through 5 of the HCO(+) vibrational states (03(1)0) and (03(3)0), respectively. Extrapolation of autoionizing series locates the positions of these rovibrational states to within +/-0.01 cm(-1). The use of this information combined with precise ionization limits for lower vibrational states determined from earlier Rydberg extrapolations and spectroscopic information available from infrared absorption measurements enables an estimate of the force-field parameters for HCO(+) bending. These parameters include the harmonic bending frequency, omega(2) = 842.57 cm(-1), the vibrational angular momentum splitting constant, g(22) = 3.26 cm(-1), and the diagonal bending anharmonicity, x(22) = -2.53 cm(-1), separated from the off-diagonal contribution, x(12), by reference to ab initio calculations. Results of experiment on the higher vibrationally excited states of HCO(+) are compared with recent theoretical predictions. Copyright 2000 Academic Press.

Transient kinetics of substrate binding to Na+/K(+)-ATPase measured by fluorescence quenching

This paper examines the transient kinetics of substrate binding to the Na+/K(+)-ATPase labelled with iodoacetamidofluorescein (IAF) using fluorescence quenching by trinitrophenyl-ATP (TNP-ATP). Earlier work (E.H. Hellen, P.R. Pratap, 1996, Fluorescence quenching of IAF-Na+/K(+)-ATPase via energy transfer to TNP-labelled nucleotide, Proceedings of the VIIIth International Conference on the Na+/K(+)-ATPase, in press) has shown that TNP-nucleotide binds to specific sites (from which unlabelled nucleotide can displace it) and nonspecific sites (from which unlabelled nucleotide cannot displace it). Under stopped-flow conditions, quenching of IAF-enzyme fluorescence was well described by a stretched exponential (F(t) = F infinity + delta F exp[-Bt alpha]). Physically, this function may be interpreted in terms of its inverse Laplace transform phi (k), which describes a distribution of rate-constants; alpha reflects the width of this distribution. As TNP-ATP concentration increased, alpha decreased, reflecting TNP-ATP binding to sites with higher energy barriers. alpha decreased by about the same amount with increasing [TNP-ATP] in the presence of saturating ATP, indicating that the distribution of rate-constants is largely associated with the nonspecific binding sites. However, alpha was significantly less than 1 for ATP-induced fluorescence recovery in the presence of TNP-ATP, indicating that rate-constants associated with specific binding site are also distributed. The distribution of rate-constants for binding to the specific site indicates a distribution in the energy of the transition state for substrate binding. These results suggest that the specific binding site (in either the empty or the full state) may exist in a series of conformations separated by small energy barriers. However, the energy barriers for binding associated with these conformations are significantly distributed.

Iodine insufficiency and neonatal hyperthyrotropinaemia in Hong Kong

OBJECTIVES

23% of the neonatal hypothyroidism in Hong Kong is transient. The present study aims to evaluate iodine excretion in healthy pregnant women in Hong Kong and to determine whether iodine insufficiency may occur in the local population to account for the type of neonatal thyroid dysfunction seen in our screening programme.

SUBJECTS

Pilot screening of urinary iodine excretion was determined in 253 healthy pregnant women between 32 and 36 weeks gestation. Fetal and maternal thyroid function in relation to urinary iodine excretion was evaluated in another 55 pregnant women who had given birth to infants with cord blood TSH > or = 16 mIU/I (95th percentile of the cord blood TSH screening programme) and the results were compared to a control group of 160 healthy women whose infants had cord blood TSH < 16 mIU/I.

RESULTS

Using a cut-off value of 0.79 mumol/l, a level as defined by WHO as iodine deficiency, we found that 35.8% of the pregnant women had urinary iodine concentrations below this cut off value. We demonstrated that the existence of borderline iodine supply affected the maternal and fetal thyroid function as evidenced by (i) a negative correlation between maternal TSH and urinary iodine concentration, (ii) higher cord blood TSH in those infants whose mothers had a low urinary iodine concentration as compared to those in whose mothers it was normal, (iii) women who had given birth to infants with cord blood TSH > or = 16 mIU/I had lower urinary iodine concentrations and serum fT4 levels as compared to mothers who had given birth to infants with normal cord TSH levels, and their offspring also had higher cord blood thyroglobulin levels.

CONCLUSION

Although Hong Kong is not a goitrous area, borderline iodine deficiency exists. Iodization of salt in our community could obviate the necessity for iodine supplements in pregnant women and other at-risk groups.

Kinetics of conformational changes associated with potassium binding to and release from Na+/K(+)-ATPase

The Na+/K(+)-ATPase functions in cells to couple energy from the hydrolysis of ATP to the transport Na+ out and K+ in. The fluorescent probe IAF (iodoacetamidofluorescein) covalently binds to this enzyme, reporting conformational changes without inhibiting enzyme activity. This paper describes experiments using dog kidney enzyme labeled with IAF to examine kinetics of conformational changes resulting from added Na+ and K+, measured in terms of steady-state and stopped-flow fluorescence changes. Kinetics of these fluorescence changes were examined as a function of temperature from two initial conditions: (a) enzyme in the high-fluorescence form (E(high)) was rapidly mixed with varying [K+]; and (b) enzyme in the low-fluorescence form (E(low)) was rapidly mixed with varying [ATP]. These experiments showed: (1) The rate constant for the fluorescence change from E(high) to E(low) was much larger than that for the opposite transition, E(low) to E(high); (2) the apparent free energy of activation (Ea(app)) for the two transitions were different (as estimated from Arrhenius plots); (3) under steady-state conditions, IAF fluorescence did not change when ATP was added to E(low)(K+) in the absence of Na+; (4) the apparent free energy of activation was independent of [K+] for the E(high) to E(low) transition (at 16.4 kcal/mol) but increased with [ATP] for the E(low) to E(high) transition; (5) Ea(app) for the E(low) to E(high) transition with 1 mM ATP was approximately the same as that in the absence of ATP (34 kcal/mol). These results can be interpreted as: (i) in the transition from E(low) to E(high), IAF reported a conformational change that occurred after K+ release to the intracellular side and which is involved in Na+ binding; (ii) Ea(app) increased with [ATP], while increasing the entropy of the transition state. Thus, ATP appeared to destabilize the enzyme during the transition from E(low) to E(high).

Existence of iodine deficiency in Hong Kong--a coastal city in southern China

OBJECTIVE

Iodine deficiency is a serious public health problem worldwide which is associated with mental retardation and cretinism. In view of a high incidence of transient neonatal hypothyroidism and a relatively high mean cord blood thyrotropin (TSH) concentration, a pilot study was carried out to analyse the urine iodine excretion in Hong Kong, a coastal city in the southern part of China.

DESIGN

Early morning urine was collected from healthy volunteers including children (n = 104), adults (n = 112) and elderly subjects (n = 349). A semi-quantitative questionnaire survey on the pattern of food intake was conducted in the adults and elderly.

RESULTS

45.3% of the children, 51.7% of the adults and 55.3% of the elderly had urine iodine concentration below the criteria for iodine sufficiency (< 0.79 mumol/l). Iodine content in the drinking water and salt was low. A dietary survey revealed that seafood was not commonly consumed. 50-80% of the subjects never consumed high-iodine containing food such as seaweed, kelp or laver, and only 50% consumed seawater fish daily.

CONCLUSION

We confirmed that although Hong Kong is a non-goitrous area, iodine insufficiency exists. It is unsafe to assume that iodine deficiency does not exist in coastal urban areas.

The Howard University Hospital Transplant and Dialysis Support Group: twenty years and going strong

This article discusses group therapy as part of a multidisciplinary approach to the management of the various psychological and physical rehabilitation concerns posed by kidney and liver transplant candidates and recipients at Howard University Hospital in Washington, DC. The group's history, format, intervention foci, and roles of clinicians and patients attending the group are described and evaluated. Given the relative paucity of research literature in this area, the authors offer recommendations for empirical evaluation of the benefits of multidisciplinary group psychotherapy in ameliorating physical and emotional suffering and prolonging life among transplant patients.

Rapid kinetic analyses of the Na+/K(+)-ATPase distinguish among different criteria for conformational change

The Na+/K(+)-ATPase couples the hydrolysis of ATP to the transport of Na+ and K+ via a phosphorylated intermediate and conformational changes. In order to identify these conformational changes, we have probed the sequence of steps from EP(3Na+ in) to EP + 3Na+ out with three fluorescent probes (IAF: 5-iodoacetamidofluorescein; BIPM: N-[p-(2-benzimidazolyl)phenyl]maleimide; and RH421) and the sensitivity of their fluorescence change to oligomycin and divalent cations (Ca2+ and Mn2+). The magnitude (% delta F) and rate constant (k(obs)) of ATP-induced fluorescence changes were measured on a fluorescence stopped-flow apparatus, and yielded the following results. (a) With RH421, k(obs) and % delta F varied with [Na+] (maximal k(obs) = 100 s-1, K1/2 = 6 mM; % delta Fmax = 6%, K1/2 = 1 mM); these values are comparable to those previously reported using IAF-labeled enzyme (Pratap, P.R., Robinson, J.D. and Steinberg, M.I. (1991) Biochim. Biophys. Acta 1069, 288-298). (b) With BIPM-labeled enzyme k(obs) did not vary with [Na+] over the range tested, and was twice as high as the maximum k(obs) for RH421. (c) Treatment with oligomycin reduced k(obs) for all three probes to about the same level (approximately 1-2 s-1) while % delta Fmax was largely unaffected. (d) Replacing Mg2+ with Ca2+ had similar effects to treatment with oligomycin. (e) RH421 fluorescence change was completely abolished in the presence of oligomycin and Ca2+. (f) Replacing Mg2+ with Mn2+ decreased IAF fluorescence, i.e., put the enzyme in an E2-like form, reduced k(obs), and rendered oligomycin less effective in reducing k(obs). From these results, we conclude: (a) the release of the second/third Na+ is the rate-limiting step for the conformational change measured by IAF and charge transfer measured with RH421; (b) BIPM indicates an earlier step, either the deocclusion of Na+ and/or the release of the first Na+; (c) oligomycin blocks Na+ deocclusion, and this step is sensitive to the divalent cation used to activate enzyme phosphorylation; and (d) Ca2+ slows the step reported by IAF as well. These experiments indicate that a simple model with two conformations (E1 and E2) is insufficient to explain transient kinetic data.

Improved mammography with a reduced radiation dose

A 2-cm-high focused air-interspaced grid with a 7:1 ratio and eight lamellae per inch was devised. The grid is arc-shaped and pivots on its focal point, the anode-cathode axis. Milliamperage was 35% less for breast phantom radiographs obtained with the new grid versus those obtained with a conventional 5:1 mammographic grid. In a comparison study of five mammograms, each evaluated for five parameters, the images obtained with the new grid were judged to be of equal or better quality than those obtained with a conventional grid in 17 of 20 comparisons.

The requirement of low calcium dialysate in patients on continuous ambulatory peritoneal dialysis receiving calcium carbonate as a phosphate binder

In the present study we investigated the requirement of low calcium dialysate in 35 patients on continuous ambulatory peritoneal dialysis (CAPD) receiving calcium carbonate as the sole phosphate binder over a 12-month period. Patients with corrected serum calcium > or = 2.85 mmol/L after switching to oral calcium carbonate were given 1 to 3 2-litre exchanges of 2.5 mEq/L calcium dialysate. Serum phosphate level dropped from the pretreatment value of 2.95 +/- 0.62 to a level of between 1.70 +/- 0.41 to 2.03 +/- 0.44 mmol/L 2 weeks after therapy. Corrected serum calcium level increased significantly from 2 weeks onwards. Serum alkaline phosphatase rose initially at 2 and 6 weeks and decreased from 3 months onwards. Serum parathyroid hormone level dropped significantly from a mean pretreatment level of 569 to 320 pg/ml after 12 months (p < 0.001). Serum aluminum decreased significantly from a mean of 1.04 to 0.65 umol/L (p < 0.01). Daily calcium carbonate requirement fluctuated but tended to increase till 8 months and plateaued and ranged from 2.61 +/- 0.57 to 3.98 +/- 2.11 gm. The daily requirement of low calcium dialysate followed a similar trend with approximately three-quarters of patients ultimately requiring at least 1 bag of low calcium dialysate. Eight patients did not require low calcium dialysate. Patients who required low calcium dialysate were significantly older, had a significantly lower pretreatment serum parathyroid hormone and higher serum aluminum levels than those who did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Lovastatin in glomerulonephritis patients with hyperlipidaemia and heavy proteinuria

Lovastatin, a 3-hydroxy-3-methylglutaryl coenzyme A inhibitor, was given to 14 patients with unremittent nephrotic syndrome (heavy proteinuria with hyperlipidaemia) for 6 months. Treatment was started at an initial dose of 20 mg/day, increasing to a maximum of 80 mg/day. Treatment was well tolerated except in two patients: one developed rhabdomyolysis and one severe hypertriglyceridaemia requiring an additional antihyperlipidaemic agent. Lovastatin was effective in reducing serum cholesterol, LDL-C and apolipoprotein B in the remaining 12 patients. Cholesterol was reduced by 31% from 8.24 +/- 0.49 mmol/l (mean +/- SEM) to 5.7 +/- 0.18 mmol/l after 6 months (P less than 0.001). LDL-C was normalized to 3.26 +/- 0.21 mmol/l from a pretreatment value of 5.76 +/- 0.48 mmol/l (P less than 0.001), a decrease of 43%. Serum apolipoprotein B was also normalized to 1.11 +/- 0.09 g/l from a basal level of 1.51 +/- 0.10 g/l (P less than 0.05). Triglyceride, HDL-C and apolipoprotein A1 concentrations were unchanged. Proteinuria as well as renal albumin clearance were unchanged. GFR by plasma radioisotope Cr-EDTA clearance for the whole group was unaltered by treatment. However, among those with relatively good pretreatment renal function (GFR greater than 70 ml/min per 1.73 m2), GFR increased at the end of 6 months' treatment (118.2 +/- 15 ml/min per 1.73 m2 versus 77.6 +/- 8.4 ml/min per 1.73 m2 in wash-out phase).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of choline on Na(+)- and K(+)-interactions with the Na+/K(+)-ATPase

Choline chloride, 100 mM, stimulates Na+/K(+)-ATPase activity of a purified dog kidney enzyme preparation when Na+ is suboptimal (9 mM Na+ and 10 mM K+) and inhibits when K+ is suboptimal (90 mM Na+ and 1 mM K+), but has a negligible effect at optimal concentrations of both (90 mM Na+ and 10 mM K+). Stimulation occurs at low Na+ to K+ ratios, but not at those same ratios when the actual Na+ concentration is high (90 mM). Stimulation decreases or disappears when incubation pH or temperature is increased or when Li+ is substituted for K+ or Rb+. Choline+ also reduces the Km for MgATP at the low ratio of Na+ to K+ but not at the optimal ratio. In the absence of K+, however, choline+ does not stimulate at low Na+ concentrations: either in the Na(+)-ATPase reaction or in the E1 to E2P conformational transition. Together, these observations indicate that choline+ accelerates the rate-limiting step in the Na+/K(+)-ATPase reaction cycle, K(+)-deocclusion; consequently, optimal Na+ concentrations reflect Na+ accelerating that step also. Thus, the observed K0.5 for Na+ includes high-affinity activation of enzyme phosphorylation and low-affinity acceleration of K(+)-deocclusion. Inhibition of Na+/K(+)-ATPase and K(+)-nitrophenylphosphatase reactions by choline+ increases as the K(+)-concentration is decreased; the competition between choline+ and K+ may represent a similar antagonism between conformations selected by choline+ and by K+.

The reaction sequence of the Na+/K(+)-ATPase: rapid kinetic measurements distinguish between alternative schemes

Conformational changes between E1 and E2 enzyme forms of a dog kidney Na+/K(+)-ATPase preparation labeled with 5-iodoacetamidofluorescein were followed with a stopped-flow fluorimeter, in terms of the rate constant, kobs, and the steady-state magnitude, % delta F of fluorescence change. On rapid mixing of enzyme plus Mg2+ plus Na+ with saturating (0.5 mM) ATP in the absence of K+, kobs varied with Na+ concentration in the range 0-155 mM, with a K1/2 of 10 mM, while % delta F was relatively insensitive to Na+, with a K1/2 of 0.5 mM. Oligomycin reduced kobs by 98-99% for Na+ greater than or equal to 10 mM, but only by 50% for Na+ = 1 mM; % delta F was reduced at most by 20%. At 155 mM Na+, both kobs and % delta F changed if K+ was present with the enzyme. kobs decreased by 50% when K+ was increased from 0 to 0.2 mM, but increased when K+ was varied in the range 0.2-5 mM. K+ increased % delta F by a factor of 3 with a K1/2 of 0.3-0.5 mM as measured in both stopped-flow and steady-state experiments. These data are considered in terms of the derived presteady-state equations for two alternate schemes for the enzyme, with the E1P to E2P conformational change either preceding (Albers-Post) or following (Nørby-Yoda-Skou) Na+ transport and release. The analysis indicates that: (i) Na+ must be released before the conformational transition, from an E1 form; (ii) the step in which the second and/or third Na+ is released is rate-limiting, but this release is accelerated by Na+; and (iii) the release is also accelerated by K+ acting with low affinity (possibly at extracellular sites).