Molecular simulations and free-energy calculations suggest conformation-dependent anion binding to a cytoplasmic site as a mechanism for Na+/K+-ATPase ion selectivity.

Na+/K+-ATPase transports Na+ and K+ ions across the cell membrane via an ion-binding site becoming alternatively accessible to the intra- and extracellular milieu by conformational transitions that confer marked changes in ion-binding stoichiometry and selectivity. To probe the mechanism of these changes, we used molecular simulation and free-energy perturbation approaches to identify probable protonation states of Na+- and K+-coordinating residues in E1P and E2P conformations of Na+/K+-ATPase. Analysis of these simulations revealed a molecular mechanism responsible for the change in protonation state: the conformation-dependent binding of an anion (a chloride ion in our simulations) to a previously unrecognized cytoplasmic site in the loop between transmembrane helices 8 and 9, which influences the electrostatic potential of the crucial Na+-coordinating residue Asp926 This mechanistic model is consistent with experimental observations and provides a molecular-level picture of how E1P to E2P enzyme conformational transitions are coupled to changes in ion-binding stoichiometry and selectivity.

Efficacy and Safety of Once-Daily Dapsone Gel, 7.5% for Treatment of Adolescents and Adults With Acne Vulgaris: First of Two Identically Designed, Large, Multicenter, Randomized, Vehicle-controlled Trials.

BACKGROUND: Treatment of acne vulgaris (acne) with dapsone gel, 5% requires twice-daily dosing, and some patients may not adhere to this regimen.
OBJECTIVE: The objective of this study was to assess the efficacy and safety of a new, once-daily formulation of dapsone gel, 7.5%, with a 50% higher dapsone concentration, versus vehicle over 12 weeks in patients with acne.
METHODS: This 12-week, randomized, double-blind, vehicle-controlled, multicenter clinical trial enrolled patients with moderate acne aged 12 years and older with 20 to 50 inflammatory lesions and 30 to 100 noninflammatory lesions on the face, and an acne grade of 3 (moderate) on the Global Acne Assessment Score (GAAS). Patients were randomized to receive topical dapsone gel, 7.5% or vehicle once daily for 12 weeks. Investigators assessed GAAS success rate (proportion of patients with GAAS of 0 or 1) and percent change from baseline in inflammatory, noninflammatory, and total lesions.
RESULTS: The intent-to-treat population comprised 2102 patients, 1044 in the dapsone gel, 7.5% group and 1058 in the vehicle group. At week 12, 29.9% of patients in the dapsone gel, 7.5% group and 21.2% in the vehicle group (P<.001) had GAAS success. Mean inflammatory lesions decreased by 55.5% and 49.0%, noninflammatory lesions decreased by 44.4% and 38.4%, and total lesions decreased by 48.7% and 42.4% in the dapsone gel, 7.5% and vehicle groups (all P<.001), respectively, at week 12. The incidence of adverse events was similar in the dapsone gel, 7.5% (19.1%) and vehicle (20.6%) groups. Most events in both groups were mild or moderate in severity. Most patients receiving dapsone gel, 7.5% and vehicle had a severity rating of "none" for stinging/burning, dryness, scaling, and erythema scales at all time points.
CONCLUSIONS: Dapsone gel, 7.5% applied topically once daily is an effective, safe, and well-tolerated treatment for acne.

J Drugs Dermatol. 2016;15(5):553-561.

Identification of electric-field-dependent steps in the Na(+),K(+)-pump cycle.

The charge-transporting activity of the Na(+),K(+)-ATPase depends on its surrounding electric field. To isolate which steps of the enzyme's reaction cycle involve charge movement, we have investigated the response of the voltage-sensitive fluorescent probe RH421 to interaction of the protein with BTEA (benzyltriethylammonium), which binds from the extracellular medium to the Na(+),K(+)-ATPase's transport sites in competition with Na(+) and K(+), but is not occluded within the protein. We find that only the occludable ions Na(+), K(+), Rb(+), and Cs(+) cause a drop in RH421 fluorescence. We conclude that RH421 detects intramembrane electric field strength changes arising from charge transport associated with conformational changes occluding the transported ions within the protein, not the electric fields of the bound ions themselves. This appears at first to conflict with electrophysiological studies suggesting extracellular Na(+) or K(+) binding in a high field access channel is a major electrogenic reaction of the Na(+),K(+)-ATPase. All results can be explained consistently if ion occlusion involves local deformations in the lipid membrane surrounding the protein occurring simultaneously with conformational changes necessary for ion occlusion. The most likely origin of the RH421 fluorescence response is a change in membrane dipole potential caused by membrane deformation.

Membrane potential-dependent inhibition of the Na+,K+-ATPase by para-nitrobenzyltriethylammonium bromide.

Membrane potential (V(M))-dependent inhibitors of the Na(+),K(+)-ATPase are a new class of compounds that may have inherent advantages over currently available drugs targeting this enzyme. However, two questions remain unanswered regarding these inhibitors: (1) what is the mechanism of V(M)-dependent Na(+),K(+)-ATPase inhibition, and (2) is their binding affinity high enough to consider them as possible lead compounds? To address these questions, we investigated how a recently synthesized V(M)-dependent Na(+),K(+)-ATPase inhibitor, para-nitrobenzyltriethylamine (pNBTEA), binds to the enzyme by measuring the extracellular pNBTEA concentration and V(M) dependence of ouabain-sensitive transient charge movements in whole-cell patch-clamped rat cardiac ventricular myocytes. By analyzing the kinetics of charge movements and the steady-state distribution of charge, we show that the V(M)-dependent properties of pNBTEA binding differ from those for extracellular Na(+) and K(+) binding, even though inhibitor binding is competitive with extracellular K(+). The data were also fit to specific models for pNBTEA binding to show that pNBTEA binding is a rate-limiting V(M)-dependent reaction that, in light of homology models for the Na(+),K(+)-ATPase, we interpret as a transfer reaction of pNBTEA from a peripheral binding site in the enzyme to a site near the known K(+) coordination sites buried within the transmembrane helices of the enzyme. These models also suggest that binding occurs with an apparent affinity of 7 µM. This apparent binding affinity suggests that high-affinity V(M)-dependent Na(+),K(+)-ATPase inhibitors should be feasible to design and test as specific enzyme inhibitors.

Evaluating spatial and network properties of NMDA-dependent neuronal connectivity in mixed cortical cultures.

A technique combining fluorescence imaging with Ca2+ indicators and single-cell laser scanning photostimulation of caged glutamate (LSPS) allowed identification of functional connections between individual neurons in mixed cultures of rat neocortical cells as well as observation of synchronous spontaneous activity among neurons. LSPS performed on large numbers of neurons yielded maps of functional connections between neurons and allowed calculation of neuronal network parameters. LSPS also provided an indirect measure of excitability of neurons targeted for photostimulation. By repeating LSPS sessions with the same neurons, stability of connections and change in the number and strength of connections were also determined. Experiments were conducted in the presence of bicuculline to study in detail the properties of excitatory neurotransmission. The AMPA receptor inhibitor, 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX), abolished synchronous neuronal activity but had no effect on connections mapped by LSPS. In contrast, the NMDA receptor inhibitor, 2-Amino-5-phosphono-pentanoic acid (APV), dramatically decreased the number of functional connections between neurons while also affecting synchronous spontaneous activity. Functional connections were also decreased by increasing extracellular Mg2+ concentration. These data demonstrated that LSPS mapping interrogates NMDA receptor-dependent connectivity between neurons in the network. In addition, a GluN2A-specific inhibitor, NVP-AAM077, decreased the number and strength of connections between neurons as well as neuron excitability. Conversely, the GluN2A-specific positive modulator, GNE-0723, increased these same properties. These data showed that LSPS can be used to directly study perturbations in the properties of NMDA receptor-dependent connectivity in neuronal networks. This approach should be applicable in a wide variety of in vitro and in vivo experimental preparations.

Glutamatergic signaling by mesolimbic dopamine neurons in the nucleus accumbens.

Recent evidence suggests the intriguing possibility that midbrain dopaminergic (DAergic) neurons may use fast glutamatergic transmission to communicate with their postsynaptic targets. Because of technical limitations, direct demonstration of the existence of this signaling mechanism has been limited to experiments using cell culture preparations that often alter neuronal function including neurotransmitter phenotype. Consequently, it remains uncertain whether glutamatergic signaling between DAergic neurons and their postsynaptic targets exists under physiological conditions. Here, using an optogenetic approach, we provide the first conclusive demonstration that mesolimbic DAergic neurons in mice release glutamate and elicit excitatory postsynaptic responses in projection neurons of the nucleus accumbens. In addition, we describe the properties of the postsynaptic glutamatergic responses of these neurons during experimentally evoked burst firing of DAergic axons that reproduce the reward-related phasic population activity of the mesolimbic projection. These observations indicate that, in addition to DAergic mechanisms, mesolimbic reward signaling may involve glutamatergic transmission.

A randomized, placebo-controlled, double-blind study to evaluate the efficacy of a citrus bioflavanoid blend in the treatment of senile purpura.

BACKGROUND: Senile purpura is a common, chronic skin condition affecting more than 10 percent of individuals over the age of 50. Despite being a benign condition, the continual development of purpura lesions in afflicted patients is frequently a source of significant visual and social concern. To date, there are no known effective treatments for this condition. OBJECTIVES: To evaluate the efficacy of a novel nutraceutical citrus bioflavonoid blend in improving the skin's appearance in patients with senile purpura. METHODS: A six-week, randomized, multicenter, placebo-controlled, double-blind study was conducted to determine whether a uniquely formulated, oral citrus bioflavonoid supplement could treat active lesions of senile purpura while preventing new lesions from arising. Seventy patients with senile purpura were enrolled and 67 completed the study. Subjects were randomized into two groups receiving either a citrus bioflavonoid blend or placebo medication, which was taken orally twice daily for six weeks. Clinical evaluations were performed by blinded investigators at two locations. RESULTS: A statistically significant reduction in the number of new purpura lesions in the skin area undergoing clinical study was documented. At the end of six weeks, the citrus bioflavonoid blend treated group showed a 50 percent reduction in purpura lesions from baseline. Patient self-assessment of the effectiveness of the medication echoed the results of an investigator global assessment with a statistically significant improvement in the skin's appearance noted by the patients receiving the active medication. No adverse effects were noted by either the patients or investigators. CONCLUSION: This new treatment appears to both safely and effectively diminish skin bruising in patients with senile purpura.

Quaternary benzyltriethylammonium ion binding to the Na,K-ATPase: a tool to investigate extracellular K+ binding reactions.

This study examined how the quaternary organic ammonium ion, benzyltriethylamine (BTEA), binds to the Na,K-ATPase to produce membrane potential (V(M))-dependent inhibition and tested the prediction that such a V(M)-dependent inhibitor would display electrogenic binding kinetics. BTEA competitively inhibited K(+) activation of Na,K-ATPase activity and steady-state (86)Rb(+) occlusion. The initial rate of (86)Rb(+) occlusion was decreased by BTEA to a similar degree whether it was added to the enzyme prior to or simultaneously with Rb(+), a demonstration that BTEA inhibits the Na,K-ATPase without being occluded. Several BTEA structural analogues reversibly inhibited Na,K-pump current, but none blocked current in a V(M)-dependent manner except BTEA and its para-nitro derivative, pNBTEA. Under conditions that promoted electroneutral K(+)-K(+) exchange by the Na,K-ATPase, step changes in V(M) elicited pNBTEA-activated ouabain-sensitive transient currents that had similarities to those produced with the K(+) congener, Tl(+). pNBTEA- and Tl(+)-dependent transient currents both displayed saturation of charge moved at extreme negative and positive V(M), equivalence of charge moved during and after step changes in V(M), and similar apparent valence. The rate constant (k(tot)) for Tl(+)-dependent transient current asymptotically approached a minimum value at positive V(M). In contrast, k(tot) for pNBTEA-dependent transient current was a "U"-shaped function of V(M) with a minimum value near 0 mV. Homology models of the Na,K-ATPase alpha subunit suggested that quaternary amines can bind to two extracellularly accessible sites, one of them located at K(+) binding sites positioned between transmembrane helices 4, 5, and 6. Altogether, these data revealed important information about electrogenic ion binding reactions of the Na,K-ATPase that are not directly measurable during ion transport by this enzyme.

E2P-like states of plasma membrane Ca2+­ATPase characterization of vanadate and fluoride-stabilized phosphoenzyme analogues.

The plasma membrane Ca2+­ATPase (PMCA) belongs to the family of P-type ATPases, which share the formation of an acid-stable phosphorylated intermediate as part of their reaction cycle. The crystal structure of PMCA is currently lacking. Its abundance is approximately 0.1% of the total protein in the membrane, hampering efforts to produce suitable crystals for X-ray structure analysis. In this work we characterized the effect of beryllium fluoride (BeFx), aluminium fluoride (AlFx) and magnesium fluoride (MgFx) on PMCA. These compounds are known inhibitors of P-type ATPases that stabilize E2P ground, E2·P phosphoryl transition and E2·Pi product states. Our results show that the phosphate analogues BeFx, AlFx and MgFx inhibit PMCA Ca2+­ATPase activity, phosphatase activity and phosphorylation with high apparent affinity. Ca2+­ATPase inhibition by AlFx and BeFx depended on Mg2+ concentration indicating that this ion stabilizes the complex between these inhibitors and the enzyme. Low pH increases AlFx and BeFx but not MgFx apparent affinity. Eosin fluorescent probe binds with high affinity to the nucleotide binding site of PMCA. The fluorescence of eosin decreases when fluoride complexes bind to PMCA indicating that the environment of the nucleotide binding site is less hydrophobic in E2P-like states. Finally, measuring the time course of E → E2P-like conformational change, we proposed a kinetic model for the binding of fluoride complexes and vanadate to PMCA. In summary, our results show that these fluoride complexes reveal different states of phosphorylated intermediates belonging to the mechanism of hydrolysis of ATP by the PMCA.

Diclofenac sodium 3% gel in the treatment of actinic keratoses postcryosurgery.

BACKGROUND: Actinic keratoses are increasingly common skin lesions that are evaluated and treated by dermatologists on a daily basis. It is estimated that more than 90% of actinic keratoses in the US are treated by destructive therapies, such as cryosurgery. The purpose of this study was to evaluate the efficacy of sequential therapy of cryosurgery followed by diclofenac sodium 3% gel. METHODS: This prospective, double-arm, multicenter, open-label, phase 4 study was performed at 82 community dermatology centers in the US. A total of 714 subjects who had a clinical diagnosis of actinic keratosis with between 5 and 15 lesions contained in a target area such as the forehead, scalp, and hands were enrolled in the study. These subjects were randomized into 2 arms of the study: cryosurgery alone and cryosurgery followed by diclofenac sodium 3% gel for a period of 90 days. Lesion counts were assessed at baseline, and 45, 75, 105, and 135 days after cryosurgery. RESULTS: Of the 521 patients enrolled in the study who successfully completed all of the visits concluding on day 135, 277 were in the cryosurgery alone arm and 244 were in the cryosurgery followed by diclofenac sodium 3% gel arm. At the conclusion of the study, 46% of the subjects in the cryosurgery followed by the use of diclofenac sodium 3% gel arm achieved 100% cumulative (target plus new lesions) lesion clearance compared to 21% in the cryosurgery alone arm (P < .0001). One hundred percent target lesion clearance was achieved in 64% of the subjects in the active arm compared to 32% in the cryosurgery alone arm (P < .0001). CONCLUSIONS: With the increased prevalence of actinic keratoses, it is important to consider and evaluate emerging therapeutic options. The sequential treatment with cryosurgery followed by diclofenac sodium 3% gel for 90 days is well tolerated and can provide a therapeutic modality that may provide patients with actinic keratoses a more successful outcome than monotherapy with cryosurgery by effectively treating clinical and subclinical lesions.

Quaternary organic amines inhibit Na,K pump current in a voltage-dependent manner: direct evidence of an extracellular access channel in the Na,K-ATPase.

The effects of organic quaternary amines, tetraethylammonium (TEA) chloride and benzyltriethylammonium (BTEA) chloride, on Na,K pump current were examined in rat cardiac myocytes superfused in extracellular Na(+)-free solutions and whole-cell voltage-clamped with patch electrodes containing a high Na(+)-salt solution. Extracellular application of these quaternary amines competitively inhibited extracellular K(+) (K(+)(o)) activation of Na,K pump current; however, the concentration for half maximal inhibition of Na,K pump current at 0 mV (K(0)(Q)) by BTEA, 4.0 +/- 0.3 mM, was much lower than the K(0)(Q) for TEA, 26.6 +/- 0.7 mM. Even so, the fraction of the membrane electric field dissipated during K(+)(o) activation of Na,K pump current (lambda(K)), 39 +/- 1%, was similar to lambda(K) determined in the presence of TEA (37 +/- 2%) and BTEA (35 +/- 2%), an indication that the membrane potential (V(M)) dependence for K(+)(o) activation of the Na,K pump current was unaffected by TEA and BTEA. TEA was found to inhibit the Na,K pump current in a V(M)-independent manner, i.e., inhibition of current dissipated 4 +/- 2% of the membrane electric field. In contrast, BTEA dissipated 40 +/- 5% of the membrane electric field during inhibition of Na,K pump current. Thus, BTEA inhibition of the Na,K-ATPase is V(M)-dependent. The competitive nature of inhibition as well as the similar fractions of the membrane electric field dissipated during K(+)(o)-dependent activation and BTEA-dependent inhibition of Na,K pump current suggest that BTEA inhibits the Na,K-ATPase at or very near the enzyme's K(+)(o) binding site(s) located in the membrane electric field. Given previous findings that organic quaternary amines are not occluded by the Na,K-ATPase, these data clearly demonstrate that an ion channel-like structure provides access to K(+)(o) binding sites in the enzyme.

Metastatic gastric adenocarcinoma presenting as an enlarging plaque on the scalp.

We present a case report of metastatic gastric adenocarcinoma in which the cutaneous metastases were the first sign of disease recurrence. A 73-year-old man presented with painless red plaques on his scalp and forehead. He was diagnosed with gastric carcinoma with metastases to perigastric lymph nodes 3 1/2 years earlier. Histopathology results revealed signet-ring cells consistent with gastric adenocarcinoma. The patient failed to respond to treatment with intralesional interleukin 2, previously reported to be effective, and expired 7 months later.

Effect of acute stretch injury on action potential and network activity of rat neocortical neurons in culture.

The basis for acute seizures following traumatic brain injury (TBI) remains unclear. Animal models of TBI have revealed acute hyperexcitablility in cortical neurons that could underlie seizure activity, but studying initiating events causing hyperexcitability is difficult in these models. In vitro models of stretch injury with cultured cortical neurons, a surrogate for TBI, allow facile investigation of cellular changes after injury but they have only demonstrated post-injury hypoexcitability. The goal of this study was to determine if neuronal hyperexcitability could be triggered by in vitro stretch injury. Controlled uniaxial stretch injury was delivered to a spatially delimited region of a spontaneously active network of cultured rat cortical neurons, yielding a region of stretch-injured neurons and adjacent regions of non-stretched neurons that did not directly experience stretch injury. Spontaneous electrical activity was measured in non-stretched and stretch-injured neurons, and in control neuronal networks not subjected to stretch injury. Non-stretched neurons in stretch-injured cultures displayed a three-fold increase in action potential firing rate and bursting activity 30-60 min post-injury. Stretch-injured neurons, however, displayed dramatically lower rates of action potential firing and bursting. These results demonstrate that acute hyperexcitability can be observed in non-stretched neurons located in regions adjacent to the site of stretch injury, consistent with reports that seizure activity can arise from regions surrounding the site of localized brain injury. Thus, this in vitro procedure for localized neuronal stretch injury may provide a model to study the earliest cellular changes in neuronal function associated with acute post-traumatic seizures.

Direct effects of recurrent hypoglycaemia on adrenal catecholamine release.

In Type 1 and advanced Type 2 diabetes mellitus, elevation of plasma epinephrine plays a key role in normalizing plasma glucose during hypoglycaemia. However, recurrent hypoglycaemia blunts this elevation of plasma epinephrine. To determine whether recurrent hypoglycaemia affects peripheral components of the sympatho-adrenal system responsible for epinephrine release, male rats were administered subcutaneous insulin daily for 3 days. These recurrent hypoglycaemic animals showed a smaller elevation of plasma epinephrine than saline-injected controls when subjected to insulin-induced hypoglycaemia. Electrical stimulation of an adrenal branch of the splanchnic nerve in recurrent hypoglycaemic animals elicited less release of epinephrine and norepinephrine than in controls, without a change in adrenal catecholamine content. Responsiveness of isolated, perfused adrenal glands to acetylcholine and other acetylcholine receptor agonists was also unchanged. These results indicate that recurrent hypoglycaemia compromised the efficacy with which peripheral neuronal activity stimulates adrenal catecholamine release and demonstrate that peripheral components of the sympatho-adrenal system were directly affected by recurrent hypoglycaemia.

Multicenter prospective cohort study of the incidence of adverse events associated with cosmetic dermatologic procedures: lasers, energy devices, and injectable neurotoxins and fillers.

IMPORTANCE: Common noninvasive to minimally invasive cosmetic dermatologic procedures are widely believed to be safe given the low incidence of reported adverse events, but reliable incidence data regarding adverse event rates are unavailable to date. OBJECTIVE: To assess the incidence of adverse events associated with noninvasive to minimally invasive cosmetic dermatologic procedures, including those involving laser and energy devices, as well as injectable neurotoxins and fillers. DESIGN, SETTING, AND PARTICIPANTS: A multicenter prospective cohort study (March 28, 2011, to December 30, 2011) of procedures performed using laser and energy devices, as well as injectable neurotoxins and soft-tissue augmentation materials, among 8 geographically dispersed US private and institutional dermatology outpatient clinical practices focused on cosmetic dermatology, with a total of 23 dermatologists. Participants represented a consecutive sample of 20 399 cosmetic procedures. Data acquisition was for 3 months (13 weeks) per center, with staggered start dates to account for seasonal variation. EXPOSURES: Web-based data collection daily at each center to record relevant procedures, by category type and subtype. Adverse events were detected by (1) initial observation by participating physicians or staff; (2) active ascertainment from patients, who were encouraged to self-report after their procedure; and (3) follow-up postprocedural phone calls to patients by staff, if appropriate. When adverse events were not observed by physicians but were suspected, follow-up visits were scheduled within 24 hours to characterize these events. Detailed information regarding each adverse event was entered into an online form. MAIN OUTCOMES AND MEASURES: The main outcome was the total incidence of procedure-related adverse events (total adverse events divided by total procedures performed), as verified by clinical examination. RESULTS: Forty-eight adverse events were reported, for a rate of 0.24% (95% CI, 0.18%-0.31%). Overall, 36 procedures resulted in at least 1 adverse event, for a rate of 0.18% (95% CI, 0.13%-0.25%). No serious adverse events were reported. Adverse events were infrequently associated with known risk factors. CONCLUSIONS AND RELEVANCE: Noninvasive to minimally invasive cosmetic dermatologic procedures, including energy, neurotoxin, and filler procedures, are safe when performed by experienced board-certified dermatologists. Adverse events occur in less than 1% of patients, and most of these are minor and transient.

Na,K-pump reaction kinetics at the tip of a patch electrode: derivation of reaction kinetics for electrogenic and electrically silent reactions during ion transport by the Na,K-ATPase.

Patch-clamp electrophysiological techniques allow manipulations of electrochemical driving forces for ion transport by the Na,K-ATPase. For this reason, this technique has been used to study steady-state ion transport properties of the Na,K-ATPase. High temporal resolution during these manipulations also permits rapid reactions, such as extracellular ion-binding reactions, to be measured as charge movements when the enzyme is engaged in electroneutral ion exchange modes. Just as useful, but less widely recognized, is the ease with which electrophysiological techniques can be used to critically study reaction steps that do not directly involve ion binding. Three studies are briefly presented to show how pre-steady-state and/or steady-state electrophysiological techniques can be used to study ion-binding reactions in a novel fashion and the kinetics of electrically silent reaction steps of this enzyme. The reaction kinetics derived from each of these studies can be used to attain detailed mechanistic information about ion transport by the Na,K-ATPase.