The complete chloroplast genome of Eremurus zoae Vved. (Asphodelaceae), an endemic species of Kyrgyz Republic

Eremurus zoae Vved. 1971 is a perennial herbaceous plant in the family Asphodelaceae and an endemic species of the Kyrgyz Republic; however, its complete chloroplast genome sequence has not been reported. Here, we investigated the complete chloroplast (cp) genome of E. zoae using next-generation sequencing. The cp genome was 153,744 bp long, with a large single copy (84,020 bp), a small single copy (16,766 bp), and a pair of inverted repeats (26,479 bp). The genome encodes 132 genes, including 86 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. Phylogenetic analysis revealed that the genus Eremurus forms a monophyletic group and E. zoae is closely related to E. chinensis. This study provides a molecular foundation for future phylogenetic studies of Eremurus.

Low prevalence of Babesia hongkongensis infection in community and privately-owned cats in Hong Kong

Domestic cats are susceptible to infection with at least 11 species of Babesia. In Hong Kong, where dogs are commonly infected with B. gibsoni, a single infection in a cat by a novel species, B. hongkongensis, was reported previously. The aim of this study was to investigate the frequency of Babesia spp. detection in cats in Hong Kong. Residual blood-derived DNA from healthy free-roaming community cats (n = 239), and privately-owned cats with and without anaemia undergoing diagnostic investigations (n = 125) was tested for Babesia spp. DNA using a pan-Babesia PCR targeting mitochondrial Cytochrome B, and a B. hongkongensis specific PCR targeting 18S rRNA. Positive samples were confirmed by sequencing and comparative sequence analysis against the GenBank nucleotide database. Babesia hongkongensis was detected in 4/239 (1.7 %) community cats, and 0/125 (0.0 %) privately-owned cats. Babesia gibsoni was detected in 0/239 community cats and 1/125 (0.8 %) privately-owned cats. Cats infected with B. hongkongensis were clinically healthy at the time of sampling. The B. gibsoni-infected cat was anaemic and thrombocytopenic. Cats in Hong Kong can be infected with B. hongkongensis and B. gibsoni, albeit at low frequency. The tick vector for B. hongkongensis is yet to be identified.

Babesia gibsoni Infection in a Cat with Immune-Mediated Haemolytic Anaemia and Thrombocytopenia

Tick-borne haemoparasite Babesia gibsoni has been detected rarely in cats, in surveys of apparently healthy animals. In stored blood from a 6-year-old male-neutered domestic shorthair cat in Hong Kong, B. gibsoni DNA was detected retrospectively using PCR for Babesia spp. 18S rRNA and mitochondrial cytochrome B genes, followed by sequencing and basic local alignment search tool (BLAST) analysis. The cat presented with severe haemolytic anaemia and thrombocytopenia. The cat responded to supportive care and glucocorticoids and was clinically normal despite persistent subclinical thrombocytopenia until six months after presentation, when it succumbed to a fatal haemorrhagic episode. Necropsy revealed severe intestinal and pulmonary haemorrhage and hypocellular bone marrow with megakaryocytosis but no other causes of immune-mediated thrombocytopenia (IMTP) or immune-mediated haemolytic anaemia (IMHA). Blood stored on days 158 and 180 tested PCR negative for Babesia spp. This report demonstrates that geographic range of B. gibsoni detection in cats includes Hong Kong. The exclusion of other causes suggests that B. gibsoni might have potentially played a role in triggering immune-mediated disease in this case.

Risk factors of COVID-19 mortality: a systematic review of current literature and lessons from recent retracted articles

OBJECTIVE

Recently, two influential articles that reported the association of (hydroxy)chloroquine or angiotensin converting enzyme (ACE) inhibitors and coronavirus disease 2019 (COVID-19) mortality were retracted due to significant methodological issues. Therefore, we aimed to analyze the same clinical issues through an improved research method and to find out the differences from the retracted papers. We systematically reviewed pre-existing literature, and compared the results with those of the retracted papers to gain a novel insight.

MATERIALS AND METHODS

We extracted common risk factors identified in two retracted papers, and conducted relevant publication search until June 26, 2020 in PubMed. Then, we analyzed the risk factors for COVID-19 mortality and compared them to those of the retracted papers.

RESULTS

Our systematic review demonstrated that most demographic and clinical risk factors for COVID-19 mortality were similar to those of the retracted papers. However, while the retracted paper indicated that both (hydroxy)chloroquine monotherapy and combination therapy with macrolide were associated with higher risk of mortality, our study showed that only combination therapy of hydroxychloroquine and macrolide was associated with higher risk of mortality (odds ratio 2.33; 95% confidence interval 1.63-3.34). In addition, our study demonstrated that use of ACE inhibitors or angiotensin receptor blockers (ARBs) was associated with reduced risk of mortality (0.77; 0.65-0.91).

CONCLUSIONS

When analyzing the same clinical issues with the two retracted papers through a systematic review of randomized controlled trials and relevant cohort studies, we found out that (hydroxy)chloroquine monotherapy was not associated with higher risk of mortality, and that the use of ACE inhibitors or ARBs was associated with reduced risk of mortality in COVID-19 patients.

Systematic review of the influence of chemotherapy-associated liver injury on outcome after partial hepatectomy for colorectal liver metastases

BACKGROUND

The impact of chemotherapy-associated liver injury (CALI) on postoperative outcome in patients undergoing partial hepatectomy for colorectal liver metastases (CRLM) remains controversial. The objective of this study was to clarify the effect of CALI (sinusoidal dilatation (SD), steatosis and steatohepatitis) on postoperative morbidity and mortality by investigating a large data set from multiple international centres.

METHODS

PubMed and Embase were searched for studies published between 1 January 2004 and 31 December 2013 with keywords 'chemotherapy', 'liver resection', 'outcome' and 'colorectal metastases' to identify potential collaborating centres. Univariable and multivariable analyses were performed using binary logistic regression models, with results presented as odds ratios (ORs) with 95 per cent confidence intervals.

RESULTS

A consolidated database comprising 788 patients who underwent hepatectomy for CRLM in eight centres was obtained. In multivariable analyses, severe SD was associated with increased major morbidity (Dindo-Clavien grade III-V; OR 1·73, 95 per cent c.i. 1·02 to 2·95; P = 0·043). Severe steatosis was associated with decreased liver surgery-specific complications (OR 0·52, 95 per cent c.i. 0·27 to 1·00; P = 0·049), whereas steatohepatitis was linked to an increase in these complications (OR 2·08, 1·18 to 3·66; P = 0·012). Subgroup analysis showed that lobular inflammation was the sole component associated with increased overall morbidity (OR 2·22, 1·48 to 3·34; P = 0·001) and liver surgery-specific complications (OR 3·35, 2·11 to 5·32; P < 0·001). Finally, oxaliplatin treatment was linked to severe SD (OR 2·74, 1·67 to 4·49; P < 0·001).

CONCLUSION

An increase in postoperative major morbidity and liver surgery-specific complications was observed after partial hepatectomy in patients with severe SD and steatohepatitis. Postoperative liver failure occurred more often in patients with severe SD.

Survival benefit of liver resection for Barcelona Clinic Liver Cancer stage B hepatocellular carcinoma

Background

Although transarterial chemoembolization is recommended as the standard treatment for Barcelona Clinic Liver Cancer stage B hepatocellular carcinoma (BCLC-B HCC), other treatments including liver resection have been used. This study aimed to determine the survival benefit of treatment strategies including resection for BCLC-B HCC compared with non-surgical treatments.

Methods

The nationwide multicentre database of the Korean Liver Cancer Association was reviewed. Patients with BCLC-B HCC who underwent liver resection as a first or second treatment within 2 years of diagnosis and patients who received non-surgical treatment were selected randomly. Survival outcomes of propensity score-matched groups were compared.

Results

Among 887 randomly selected patients with BCLC-B HCC, 83 underwent liver resection as first or second treatment and 597 had non-surgical treatment. After propensity score matching, the two groups were well balanced (80 patients in each group). Overall median survival in the resection group was better than that for patients receiving non-surgical treatment (50·9 versus 22·1 months respectively; P &lt; 0·001). The 1-, 2-, 3- and 5-year overall survival rates in the resection group were 90, 88, 75 and 63 per cent, compared with 79, 48, 35 and 22 per cent in the no-surgery group (P &lt; 0·001). In multivariable analysis, non-surgical treatment only (hazard ratio (HR) 3·35, 95 per cent c.i. 2·16 to 5·19; P &lt; 0·001), albumin level below 3·5 g/dl (HR 1·96, 1·22 to 3·15; P = 0·005) and largest tumour size greater than 5·0 cm (HR 1·81, 1·20 to 2·75; P = 0·005) were independent predictors of worse overall survival.

Conclusion

Treatment strategies that include liver resection offer a survival benefit compared with non-surgical treatments for potentially resectable BCLC-B HCC.

Vertigo and nystagmus in orthostatic hypotension

BACKGROUND AND PURPOSE

Generalized cerebral ischaemia from cardiovascular dysfunction usually leads to presyncopal dizziness, but several studies reported a higher frequency of rotatory vertigo in cardiovascular patients. Whether generalized cerebral ischaemia due to cardiovascular disorders may produce objective vestibular dysfunction was investigated.

METHODS

Thirty-three patients with orthostatic dizziness/vertigo due to profound orthostatic hypotension and 30 controls were recruited. All participants underwent recording of eye movements during two orthostatic challenging tests: the Schellong and the squatting-standing tests. Most patients had neuroimaging, and patients with abnormal eye movements were subjected to follow-up evaluations.

RESULTS

Symptoms associated with orthostatic dizziness/vertigo included blurred vision, fainting and tinnitus. Ten (30%) of 33 patients developed rotatory vertigo and nystagmus during the Schellong (n = 5) or squatting-standing test (n = 5). Four of them showed pure downbeat nystagmus whilst five had downbeat and horizontal nystagmus with or without torsional component. Patients with orthostatic nystagmus had shorter duration of orthostatic intolerance than those without nystagmus (1.0 ± 1.6 vs. 11.0 ± 9.7 months, P < 0.001). In two patients, orthostatic nystagmus disappeared during follow-up despite the persistence of profound orthostatic hypotension.

CONCLUSIONS

Generalized cerebral ischaemia caused by orthostatic hypotension induces rotatory vertigo due to objective vestibular dysfunction. The presence of orthostatic vertigo and nystagmus has an association with the duration of orthostatic intolerance.

Endoscopic versus open release in patients with de Quervain's tenosynovitis: a randomised trial

The purpose of this study was to compare the outcome and complications of endoscopic versus open release for the treatment of de Quervain's tenosynovitis. Patients with this condition were randomised to undergo either endoscopic (n = 27) or open release (n = 25). Visual Analogue Scale (VAS) pain and Disabilities of Arm, Shoulder, and Hand (DASH) scores were measured at 12 and 24 weeks after surgery. Scar satisfaction was measured using a VAS scale. The mean pain and DASH scores improved significantly at 12 weeks and 24 weeks (p < 0.001) in both groups. The scores were marginally lower in the endoscopic group compared to the open group at 12 weeks (p = 0.012 and p = 0.002, respectively); however, only the DASH score showed a clinically important difference. There were no differences between the groups at 24 weeks. The mean VAS scar satisfaction score was higher in the endoscopic group at 24 weeks (p < 0.001). Transient superficial radial nerve injury occurred in three patients in the endoscopic group compared with nine in the open release group (p = 0.033). We conclude that endoscopic release for de Quervain's tenosynovitis seems to provide earlier improvement after surgery, with fewer superficial radial nerve complications and greater scar satisfaction, when compared with open release.

Distal metatarsal osteotomy for hallux varus following surgery for hallux valgus

We reviewed the outcome of distal chevron metatarsal osteotomy without tendon transfer in 19 consecutive patients (19 feet) with a hallux varus deformity following surgery for hallux valgus. All patients underwent distal chevron metatarsal osteotomy with medial displacement and a medial closing wedge osteotomy along with a medial capsular release. The mean hallux valgus angle improved from -11.6° pre-operatively to 4.7° postoperatively, the mean first-second intermetatarsal angle improved from -0.3° to 3.3° and the distal metatarsal articular angle from 9.5° to 2.3° and the first metatarsophalangeal joints became congruent post-operatively in all 19 feet. The mean relative length ratio of the metatarsus decreased from 1.01 to 0.99 and the mean American Orthopaedic Foot and Ankle Society score improved from 77 to 95 points. In two patients the hallux varus recurred. One was symptom-free but the other remained symptomatic after a repeat distal chevron osteotomy. There were no other complications. We consider that distal chevron metatarsal osteotomy with a medial wedge osteotomy and medial capsular release is a useful procedure for the correction of hallux varus after surgery for hallux valgus.

Comparison of the effect-site concentrations of remifentanil for Streamlined Liner of the Pharynx Airway (SLIPA) versus laryngeal mask airway SoftSealTM insertion during target-controlled infusion of propofol

This study was designed to determine the optimal dose of remifentanil required for the successful insertion of Streamlined Liner of the Pharynx Airway (SLIPA) and to compare it to that required for laryngeal mask airway (LMA) insertion in patients receiving a propofol infusion at a standard effect-site concentration. Fifty-eight patients scheduled to undergo general anaesthesia were randomly assigned to either the SLIPA (n = 29) or LMA (n = 29) group. All patients were premedicated with midazolam 0.05 mg x kg(-1) and glycopyrrolate 0.004 mg x kg(-1) intramuscularly. After the administration of lignocaine 1 mg x kg(-1) intravenously, a propofol infusion was started at an effect-site concentration of 3.5 microg x ml(-1) with a remifentanil infusion without a neuromuscular blocking agent. The remifentanil dose was determined by the modified up-and-down method starting in each group at 4 ng x ml(-1). Six minutes after induction, the airway device was inserted. Airway device insertion was classified as 'success' or 'failure' based on patient response. From the isotonic regression analysis and bootstrap distribution, the EC50 of remifentanil for SLIPA and LMA were 0.93 ng x ml(-1) (95% confidence interval [CI] 0.81 to 1.50 ng x ml(-1) and 1.36 ng x ml(-1) (95% CI 1.19 to 2.06 ng x ml(-1)) respectively, and the EC95 for SLIPA and LMA insertions were 1.90 ng x ml(-1) (95% CI 1.39 to 1.95) and 2.43 ng x ml(-1) (95% CI 1.80 to 2.46 ng x ml(-1)) respectively. Using the 83% CIs from the bootstrap distribution, EC50 for SLIPA was significantly less than that of LMA (0.83 to 1.23 vs 1.26 to 2.00, respectively) (P < 0.05). These findings suggest that the insertion of SLIPA needs about a 32% lower depth of anaesthesia than LMA insertion.

Frameshift mutations at coding mononucleotide repeats of the hRAD50 gene in gastrointestinal carcinomas with microsatellite instability

Microsatellite instability (MSI) and frameshift mutations in genes containing nucleotide repeats have been reported in a subset of colorectal and gastric carcinomas. This study describes the analysis of MSI-positive colorectal (39 cases) and gastric carcinomas (36 cases) for the presence of frameshift mutations of the six genes known to be involved in DNA repair and containing mononucleotide repeats in their coding region. Our mutational study of the 75 MSI-positive tumors revealed frequent mutations in hRAD50 (23 cases, 31%), BLM (16 cases, 21%), and hMSH6 (16 cases, 21%); rare mutations in BRCA1 (1 case, 1%) and ATM (3 cases, 4%); and no mutation in NBS1. In contrast, no frameshift mutation was found in 60 MSI-negative colorectal and gastric carcinomas. The mutation of hRAD50, a gene that is involved in the response to cellular DNA damage and forms a complex with hMRE11 and NBS1, has not been reported previously. Our results suggest that frameshift mutations of hRAD50, BLM, and hMSH6 are selected and play a role in the tumorigenesis of colorectal and gastric carcinomas with MSI. The MSI targeting of the hRAD50 and BLM genes represents an additional link between MSI and DNA repair because alteration of these genes could accelerate defective DNA repair.

Activity-dependent conduction velocity changes of A(delta) fibers in a rat model of neuropathy

Activity-dependent changes of conduction velocity (CV) and conduction block in single A(delta) fibers of primary afferent neurons were characterized in a rat model of neuropathy (NP). Injured dorsal root (DR) fiber in NP rats exhibited profoundly greater decreases of CV following impulse activity than did DR fiber in normal rats. Activity-dependent conduction block was absent up to 100 Hz of activity rate in DR fiber of NP rats, but was present above 25 Hz in normal rats. Profiles of activity dependence in sciatic fibers were similar in both NP and normal rats. These results suggest that nerve injury may alter activity-dependent hypoexcitability of A(delta) DR fibers. Furthermore, this excitability change may be responsible for the elevated pain perception in neuropathy.

Activity-dependent conduction latency changes in A beta fibers of neuropathic rats

Activity-dependent changes of the conduction latency of single A beta fibers of primary afferent neurons were characterized in both neuropathic (L4 and L6 ligated) and normal rats. Activity-dependent increases in conduction latency of dorsal root fibers in neuropathic rats were significantly stronger than those in normal rats. Different profiles of activity dependence were also observed between injured and adjacent intact dorsal root fibers of neuropathic rats. However, activity-dependent latency changes in sciatic nerves distal to the dorsal root ganglion were not different between neuropathic and normal rats. These results suggest that partial nerve injury induces activity-dependent excitability changes in the dorsal root fibers of neuropathic rat and that these changes may be responsible for the altered sensory processing such as those seen in allodynia.

Studies on the formation of phosphoenolpyruvate and citric acid cycle intermediates by neonatal piglet liver mitochondria

The capacity of mitochondria isolated from livers of 5-day-old piglets to convert pyruvate to phosphoenolpyruvate, malate and citrate has been investigated. These mitochondria have a large capacity to flux pyruvate through the pyruvate carboxylase reaction causing an accumulation of malate, citrate and phosphoenolpyruvate. As much as 70% of the pyruvate utilized during state 3 respiration can flux through the pyruvate carboxylase reaction. The data indicate that phosphoenolpyruvate from mitochondria can contribute a significant fraction of the carbon skeletons of pyruvate converted to glucose by piglet liver (estimated to be 30%).

Studies on the oxidation of isobutyrylcarnitine by beef and rat liver mitochondria

Mitochondria from beef liver oxidize isobutyrylcarnitine at approximately 50% the rate of succinate in the presence of rotenone. However, the oxidation rate of isobutyryl coenzyme A in the presence of l(-)-carnitine is very low and can be negligible in both rat and beef liver mitochondria. The limited stimulation of isobutyryl-CoA oxidation by l(-)-carnitine appears to be due to inhibition of isobutyrylcarnitine translocation rather than lack of formation of isobutyrylcarnitine. This conclusion is supported by the fact that: 1) isobutyrylcarnitine oxidation is inhibited by l(-)-carnitine; 2) some oxidation of isobutyryl-CoA is obtained when a low concentration (50 microM) of l(-)-carnitine is used; and 3) under conditions of high isobutyryl-coenzyme A and l(-)-carnitine concentrations (1 mM), isobutyryl-carnitine is produced in near theoretical amounts by these rat liver mitochondria. Other studies demonstrated that less than 25% of the carnitine isobutyryl transferase activity of beef liver mitochondria and rat liver mitochondria is located on the cytosol side of the acylcoenzyme A barrier of these mitochondria.

The effect of long-term fasting on the branched chain acylcarnitines and branched chain carnitine acyltransferases

The effect of fasting for 8 days on the levels of carnitine acyltransferases in heart, liver, liver mitochondria, skeletal muscle, skeletal muscle mitochondria, kidney, and testes in young adult male rats was determined. The specific activities of acetyl-, octanyl-, isobutyryl-, and isovaleryl-carnitine acyltransferase in mitochondria isolated from the livers of fasted animals were significantly higher than the levels of the transferases isolated from livers of fed animals. Similar results were obtained with the 500 x g supernatant fluids from liver. In contrast, the specific activities of carnitine acyltransferases of 500 x g supernatant fractions isolated from heart, skeletal muscle, kidney, and testes were the same for fed as fasted animals. The total carnitine content of liver, muscle, heart, and kidney was less in animals fasted for 8 days than in fed animals, but the amount/g of organ was higher in the animals fasted for 8 days. The amount of specific short-chain acylcarnitines in liver, muscle, and heart was determined for both fed and fasted animals. The amount of isobutyrylcarnitine and isovalerylcarnitine increased significantly in muscle from fasted animals. These data are consistent with the previous suggestion that carnitine may have a role in the metabolism of the branched-chain amino acids.

Membrane (Na+ + K+)-ATPase of canine brain, heart and kidney. Tissue-dependent differences in kinetic properties and the influence of purification procedures

Effects of commonly used purification procedures on the yield and specific activity of (Na+ + K+)-ATPase (Mg2+-dependent, Na+ + K+-activated ATP phosphohydrolase, EC 3.6.1.3), the turnover number of the enzyme, and the kinetic parameters for the ATP-dependent ouabain-enzyme interaction were compared in canine brain, heart and kidney. Kinetic parameters were estimated using a graphical analysis of non-steady state kinetics. The protein recovery and the degree of increase in specific activity of (Na+ + K+)-ATPase and the ratio between (Na+ + K+)-ATPase and Mg2+-ATPase activities during the successive treatments with deoxycholate, sodium iodide and glycerol were dependent on the source of the enzyme. A method which yields highly active (Na+ + K+)-ATPase preparations from the cardiac tissue was not suitable for obtaining highly active enzyme preparations from other tissues. Apparent turnover numbers of the brain (Na+ + K+)-ATPase preparations were not significantly affected by the sodium iodide treatment, but markedly decreased by deoxycholate or glycerol treatments. Similar glycerol treatment, however, failed to affect the apparent turnover number of cardiac enzymes preparations. Cerebral and cardiac enzyme preparations obtained by deoxycholate, sodium iodide and glycerol treatments had lower affinity for ouabain than renal enzyme preparations, primarily due to higher dissociation rate constants for the ouabain.enzyme complex. This tissue-dependent difference in ouabain sensitivity seems to be an artifact of the purification procedure, since less purified cerebral or cardiac preparations had lower dissociation rate constants. Changes in apparent association rate constants were minimal during the purfication procedure. These results indicate that the presentyl used purification procedures may alter the properties of membrane (Na+ + K+)-ATPase and affect the interaction between cardiac glycosides and the enzyme. The effect of a given treatment depends on the source of the enzyme. For the in vitro studies involving purified (Na+ + K+)-ATPase preparations, the influence of the methods used to obtain the enzyme preparation should be carefully evaluated.

Quantitation of water-soluble acylcarnitines and carnitine acyltransferases in rat tissues

The water-soluble acylcarnitines isolated from rat heart, skeletal muscle, liver, and testis have been characterized. The following acyl residues derived from the acylcarnitine fraction were found: acetyl, propionyl, isobutyryl, butyryl, alpha-methylbutyryl, isovaleryl, tiglyl, caproyl, beta-methylcrotonyl and methacrylyl. The amounts of these acylcarnitines in heart, liver, testis and skeletal muscle from fed rats were determined. Acetylcarnitine was the most abundant acylcarnitine; however, appreciable quantities of propionyl-, isobutyryl-, isovaleryl-, and tiglyl-carnitine were found. The levels of carnitine octanyltransferse, carnitine acetyltransferase and carnitine palmityltransferase activities were determined in several tissues. In addition, carnitine isovaleryltransferase and isobutyryltransferase activities were measured in heart, skeletal muscle, liver, testis and kidney. In all instances the specific activity of isobutyryltransferase was similar to the specific activity of acetyltransferase. The results are consistent with the proposal that carnitine is involved in the catabolism of branched-chain amino acids.

Isolation and identification of aliphatic short-chain acylcarnitines from beef heart: possible role for carnitine in branched-chain amino acid metabolism

Aliphatic acylearnitines isolated from a water-soluble fraction of beef heart have been characterized by gas chromatography and mass spectrometry. The following acyl residues derived from the acylcarnitine fraction were unequivocally identified: acetyl, propionyl, isobutyryl, butyryl, alpha-methylbutyryl, valeryl, isovaleryl, tiglyl, and caproyl. beta-methylcrotonyl and methacrylyl were tentatively identified. This occurrence of considerable quantities of branched-chain acylcarnitines indicates a role for carnitine in branched-chain amino acid metabolism.

Kinetics studies on the interaction between ouabain and (Na+,K+)-ATPase

The association and dissociation rate constants for the interaction of [3H]-ouabain with partially purified rat brain (Na+,K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) in vitro were estimated from the time course of the [3H]-ouabain binding observed in the presence of Na+, Mg2+ and ATP by a polynomial approximation-curve-fitting technique. The reduction of the association rate constant by K+ was greater than its reduction of the dissociation rate constant. Thus, the affinity of Na+,K+)-ATPase for ouabain was reduced by K+. The binding-site concentration was unaffected by K+. Consistent with these findings, the addition of KCl to an incubation mixture at the time when [3H]-ouabain binding to (Na+,K+)ATPase is close to equilibrium, caused an immediate decrease in bound ouabain concentration, apparently shifting towards a new, lower equilibrium concentration. Dissociation rate constants which were estimated following the termination of the ouabain-binding reaction were different from those estimated with above methods and may not be useful in predicting the ligand effects on equilibrium of the ouabain-enzyme interaction.