Mechanisms of Isoflurane-mediated Hyperpolarization of Vascular Smooth Muscle in Chronically Hypertensive and Normotensive Conditions

Background: The purpose of this study was to compare the effects of isoflurane on membrane and intracellular mechanisms that regulate vascular smooth muscle (VSM) transmembrane potential (Em; which is related to VSM tone) in the spontaneously hypertensive rat (SHR) model of essential hypertension and its normotensive Wistar-Kyoto (WKY) control.

Methods: Vascular smooth muscle Em values were measured in situ in locally denervated, superfused, intact, small (200-300-[mu]m OD) mesenteric arteries and veins in anesthetized 9- 12-week-old SHR and WKY. Effects of 1.0 minimum alveolar concentration (0.60 mm) superfused isoflurane on VSM Em were measured before and during superfusion with specific inhibitors of VSM calcium-activated (KCa) and adenosine triphosphate-regulated (KATP) potassium channels, and with endogenous mediators of vasodilatation (nitric oxide, cyclic guanosine monophosphate, protein kinase G, cyclic adenosine monophosphate, and protein kinase A).

Results: Isoflurane significantly hyperpolarized small arteries (5 +/- 3.4 mV) and veins (6 +/- 4.7 mV) (pooled SHR and WKY, mean +/- SD). Inhibition of KCa and KATP channels, cyclic adenosine monophosphate, and protein kinase A, but not nitric oxide, cyclic guanosine monophosphate, and protein kinase G, abolished such hyperpolarization equally in SHR and WKY vessels.     

A comparison of the effects of halothane and tetrodotoxin on the regional repolarization characteristics of canine Purkinje fibers

The effects of halothane, tetrodotoxin (TTX), veratridine (VTD), and alterations of extracellular calcium ion concentration [Ca++]0) on regional differences of canine Purkinje fiber action potential duration (APD50 and APD90) were investigated in vitro at a paced rate of 75 beats per min. Under control conditions (n = 15 hearts) APD90 of proximal (false tendon) fibers (289 +/- 6 ms) always exceeded (P less than or equal to 0.01) that of distal (apical) fibers (213 +/- 4 ms). Halothane (0.35-1.07 mM) reduced regional differences of APD90 by producing dose-dependent decreases of proximal APD90 without decreases of distal APD90. The regional actions of halothane were similar to those of low (0.33-1.0 microM) concentrations of the Na+ channel antagonist TTX, which also decreased proximal APD90 more than distal APD90. The actions of halothane in combination with TTX further decreased proximal APD90, whereas the Na+ channel agonist VTD, which increased proximal APD90 more than distal APD90, reversed the regional actions of halothane. Decreasing Ca++ influx by reducing [Ca++]0 from 1.8 to 0.6 mM increased proximal APD90 more than distal APD90 in a manner opposite to the regional actions of halothane. Although there was no difference between the values of APD90 obtained for each region in the presence of halothane at 0.6, 1.8, and 3.6 mM [Ca++]0, the action of halothane decreasing APD90 of proximal fibers was more prominent at 0.6 mM [Ca++]0 because of the increased APD90 of fibers under this condition. The findings are consistent with, but do not definitively prove, the hypothesis that halothane may decrease APD90 of proximal Purkinje fibers by a mechanism similar to that of TTX involving inhibition of plateau-phase inward Na+ current.     

Anesthetics and automaticity in latent pacemaker fibers: I. Effects of halothane, enflurane, and isoflurane on automaticity and recovery of automaticity from overdrive suppression in Purkinje fibers derived from canine hearts

Knowledge of arrhythmic or antiarrhythmic actions of anesthetics on automaticity of latent pacemaker fibers has relevance to the intraoperative management of patients with bradyarrhythmia due to sinus node dysfunction or heart block. The authors determined the effects of halothane, enflurane, and isoflurane on automaticity and recovery of automaticity from overdrive suppression in canine Purkinje fibers derived from normal hearts. Purkinje fibers were superfused with a modified Krebs' solution (37 degrees C) containing epinephrine (2 or 15 microM) and equilibrated with a 97% O2-3% CO2 gas mixture (control). Transmembrane action potentials (AP) were recorded using standard microelectrode techniques. Purkinje fibers were then exposed to anesthetics at vaporizer settings of 0.75 or 1.5% (halothane), 1.75 or 3.5% (enflurane), and 1 or 2% (isoflurane), which were equivalent to measured superfusate concentrations of 0.22 or 0.47 mM (halothane), 0.44 or 0.94 mM (enflurane), and 0.28 or 0.53 mM (isoflurane). Compared to control, there was no significant effect of either concentration of the anesthetics on upstroke (phase 0) depolarization, AP amplitude or duration (50% repolarization), or maximum diastolic potential. All three anesthetics increased spontaneous rate. The increase in rate with all three anesthetics was due to enhanced diastolic depolarization (rate dV/dt, phase-4 depolarization). Recovery times from overdrive suppression were determined after 30 or 60 s of pacing at drive cycle lengths of 800, 500, and 400 ms and only at higher anesthetic concentrations. Recovery of automaticity was shortened by halothane only in slowly paced fibers exposed to the lower concentration of epinephrine. Under all other conditions recovery times were not affected by halothane.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pathophysiologische Mechanismen genetischer Epilepsien

Epileptic seizures occur because of the increased excitability of neuronal cells in the brain that is of a mainly genetic origin in at least one third of all epilepsies. The so far identified mutations in inherited monogenic idiopathic epilepsies mainly affect ion channel genes and could be linked to both focal and generalized forms of inherited epilepsy. In a healthy brain, ion channels in the membranes of excitatory and inhibitory neurons are responsible for a neuronal balance. Disruption of this balance by changing the ion channel function can therefore lead to epileptic seizures. In this overview, we describe and discuss known epilepsy-associated mutations in ion channel genes, their functional consequences, and the resulting disease mechanisms.     

Dentinal hypersensitivity following scaling and root planing: comparison of low-level laser and topical fluoride treatment

The aim of this study is to compare the effectiveness of low-level laser irradiation to traditional topical fluoride treatment for treatment choices of dentinal hypersensitivity following scaling and root planing. The experimental group (15 patients) was treated with low-energy-level diode laser at each site of dentinal hypersensitivity following scaling and root planning. The control group (15 patients) received topical fluoride treatment (protective varnish for desensitization). All the patients were treated at baseline visit, and then at day 2 and 4 after the initial treatment; the pain was subjectively assessed by the patients as strong, medium, medium low, low, or no pain. Total absence of the dental hypersensitivity was reported in 26.66% of the examined group even after the second visit, compared to the control group where complete resolution of the hypersensitivity was not present after the second visit in any of the treated cases. Complete absence of pain was achieved in 86.6% of patients treated with laser and only in 26.6% in the fluoride treated group, after the third visit. Based on our findings, we conclude that low-energy biostimulative laser treatment can be successfully used for treatment of dental hypersensitivity following scaling and root planing.     

Ketamine Induces Toxicity in Human Neurons Differentiated from Embryonic Stem Cells via Mitochondrial Apoptosis Pathway

Ketamine is widely used for anesthesia in pediatric patients. Growing evidence indicates that ketamine causes neurotoxicity in a variety of developing animal models. Our understanding of anesthesia neurotoxicity in humans is currently limited by difficulties in obtaining neurons and performing developmental toxicity studies in fetal and pediatric populations. It may be possible to overcome these challenges by obtaining neurons from human embryonic stem cells (hESCs) in vitro. hESCs are able to replicate indefinitely and differentiate into every cell type. In this study, we investigated the toxic effect of ketamine on neurons differentiated from hESCs. Two-week-old neurons were treated with different doses and durations of ketamine with or without the reactive oxygen species (ROS) scavenger, Trolox. Cell viability, ultrastructure, mitochondrial membrane potential (ΔΨm), cytochrome c distribution within cells, apoptosis, and ROS production were evaluated. Here we show that ketamine induced ultrastructural abnormalities and dose- and timedependently caused cell death. In addition, ketamine decreased ΔΨm and increased cytochrome c release from mitochondria. Ketamine also increased ROS production and induced differential expression of oxidative stress-related genes. Specifically, abnormal ultrastructural and ΔΨm changes occurred earlier than cell death in the ketamine-induced toxicity process. Furthermore, Trolox significantly decreased ROS generation and attenuated cell death caused by ketamine in a dose-dependent manner. In conclusion, this study illustrates that ketamine time- and dose-dependently induces human neurotoxicity at supraclinical concentrations via ROS-mediated mitochondrial apoptosis pathway and that these side effects can be prevented by the antioxidant agent Trolox. Thus, hESC-derived neurons might provide a promising tool for studying anesthetic-induced developmental neurotoxicity and prevention strategies.     

Compounding of a topical drug with prospective natural surfactant-stabilized pharmaceutical bases: Physicochemical and in vitro/in vivo characterization - A ketoprofen case study

Recently, healthcare professionals again began realizing the benefits of preparing customized medications to meet specific patient needs. The objective of this work was to develop and evaluate simple pharmaceutical bases stabilized with natural-origin surfactant of alkyl polyglucoside (APG) type as prospective ready-to-use bases and compare them to widely used pharmacopoeial ones. Additionally, the ability of the formulated bases to sustain isopropyl alcohol was assessed as well as its influence on ketoprofen skin absorption (as a co-solvent and potential penetration enhancer). In order to evaluate the manifold characteristics a topical drug product should possess, a comprehensive characterization was performed using different techniques.Physicochemical characterization demonstrated satisfactory physical stability of APG-stabilized bases upon the addition of alcohol. In vitro release/permeation studies failed to show significant difference in ketoprofen liberation/permeation profiles from different bases. However, the extent of ketoprofen delivery in vivo was clearly increased from APG bases, relative to that obtained from pharmacopoeia quality one, implying a distinct influence of the emulsion systems’ colloidal structures. Taking also into account the rheological behavior of APG bases, revealing their ameliorated sensory characteristics, it could be concluded that the investigated APG bases could be considered as preferential option in drug compounding related to the conventional ones.     

NKG2D performs two functions in invariant NKT cells: direct TCR-independent activation of NK-like cytolysis and co-stimulation of activation by CD1d

Invariant NKT cells are important in the activation and regulation of immune responses. They can also function as CD1d-restricted killer cells. However, the role of activating innate NK-cell receptors expressed on NKT cells in triggering cytolytic function is poorly characterized. Here, we initially confirmed that the cellular stress-ligand receptor NKG2D is expressed on CD4- NKT cells, whereas most CD4+ NKT cells lack this receptor. Interestingly, NKG2D+ NKT cells frequently expressed perforin, and both NKG2D and perforin localized at the site of contact with NKG2D ligand-expressing target cells. CD4- NKT cells degranulated in response to NKG2D engagement in a redirected activation assay independent of stimulation via their invariant TCR. NKT cells killed P815 cells coated with anti-NKG2D mAb and CD1d-negative K562 tumor target cells in an NKG2D-dependent manner. Furthermore, NKG2D engagement co-stimulated TCR-mediated NKT-cell activation in response to endogenous CD1d-presented ligands or suboptimal levels of anti-CD3 triggering. These data indicate that the CD4- subset of human NKT cells can mediate direct lysis of target cells via NKG2D engagement independent of CD1d, and that NKG2D also functions as a co-stimulatory receptor in these cells. NKG2D thus plays both a direct and a co-stimulatory role in the activation of NKT cells.