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1.
J Nepal Health Res Counc ; 15(1): 7-11, 2017 Jan.
Article in English | MEDLINE | ID: mdl-28714485

ABSTRACT

BACKGROUND: Medical waste is considered as a major public health hazard. In a developing country like Nepal, there is much concern about the management practice of medical waste. This study aimed to assess Health Care Waste Management practice among Health Care Institutions in Nepal. METHODS: A cross sectional study was carried out between July 2012 to June 2013 in 62 different Health Care Institutions, selected from stratified proportionate random sampling technique from all administrative regions of Nepal. A structured questionnaire and observation checklist were used for data collection. RESULTS: The waste generation rate is found significantly correlated with bed capacity, patient flow rate and annual budget spent in the hospital. It is found significantly higher in Teaching hospital than other Health Care Institutions of Nepal. An average of 3.3 kg/day/patient of medical waste (2.0 kg/day/patient non-hazardous and 1.0 kg/day/patient hazardous waste) was generated during the study period. Further, it was found that most of the Health care wastes were not disinfected before transportation to waste disposal sites. Very limited number of Health Care Institutions had conducted Environmental Assessment. Similarly, some of the Health Care Institutions had not followed Health care waste management guideline 2009 of Nepal Government. CONCLUSIONS: We found poor compliance of medical waste management practice as per existing legislation of Government of Nepal. Hence, additional effort is needed for improvement of Health care waste management practice at Health Care Institutions of Nepal.


Subject(s)
Health Facilities/statistics & numerical data , Medical Waste Disposal/methods , Medical Waste Disposal/standards , Budgets/statistics & numerical data , Cross-Sectional Studies , Hospital Bed Capacity/statistics & numerical data , Hospitals, Teaching/statistics & numerical data , Humans , Nepal , Ownership , Residence Characteristics
2.
Skeletal Radiol ; 43(3): 345-9, 2014 Mar.
Article in English | MEDLINE | ID: mdl-24362937

ABSTRACT

OBJECTIVE: Tibial tubercle trochlear groove distance (TTD) is a significant factor in patello-femoral instability. Initially described on CT scans with the knee in full extension, the measurement has been validated on MR scans. Dedicated knee MRI coils have subsequently superseded both CT and MRI body coils for knee imaging. However, the knee rests in partial flexion within the dedicated knee coil. The objective of this study is to investigate whether images from dedicated knee MRI coils produce different TTD measurements from MR body coils. MATERIALS AND METHODS: Thirty-two symptomatic knees (27 patients) had simultaneous knee MR scans performed in both a dedicated knee coil and a body coil. TTD measurements were independently compared to assess whether the coil type used affected TTD. RESULTS: Patients' ages ranged from 10 to 27 years (mean 15 years). Mean TTD in the dedicated knee coil (partially flexed knee) was 11.3 mm compared with 19.9 mm in the body coil (that permits full knee extension). The mean difference was 8.6 mm, which was highly significant (p < 0.0001, unpaired t test). Inter-rater correlation co-efficient was 96 %. Of the knees that recorded a "normal" TTD on the dedicated knee coil, 60-100 % recorded a "pathological" TTD on body coil images, depending on which diagnostic value for "normal" cut-off was used. CONCLUSION: This study has identified a highly significant difference in TTD measurement when knees are scanned in a dedicated knee coil with the knee partially flexed, compared with an MR body coil. It is critical for surgeons and radiologists managing patello-femoral instability to appreciate this profound difference. TTD measurement taken from knees scanned in dedicated knee coils may lead to patients being falsely re-assured or erroneously denied surgery.


Subject(s)
Anatomic Landmarks/pathology , Joint Instability/pathology , Magnetic Resonance Imaging/instrumentation , Magnetics/instrumentation , Patellofemoral Joint/pathology , Tibia/pathology , Transducers , Adolescent , Adult , Child , Equipment Design , Equipment Failure Analysis , Female , Humans , Male , Reproducibility of Results , Sensitivity and Specificity , Young Adult
3.
J Nepal Health Res Counc ; 11(23): 22-5, 2013 Jan.
Article in English | MEDLINE | ID: mdl-23787520

ABSTRACT

BACKGROUND: There were about 24,000 children affected by AIDS living in Nepal in 2010; of these 5,000 AIDS orphans were in need of immediate support. The objective of this study was to investigate which model of care and support is more appropriate for improving psychosocial and economic security of AIDS orphans. METHODS: With the documented 5200 cases of AIDS orphans from 42 districts at National Association of People Living with HIV, we purposively selected five districts - one from each development region, based on the highest number of AIDS orphans reported. From five districts, 56 HIV positive double orphans aged 8-18 years and their 42 caregivers were interviewed to find their psychosocial and economic situation. RESULTS: Thirty nine (70%) orphans were found living in kinship care, while 17(30%) were living in institutional care homes. Orphans living in kinship were more optimistic, as they were backed by their close relatives 35 (90%), had birth certificates 35 (90%), ensured inherent family property 21 (54%), obtained basic needs like food, education and shelter from grandparents 23 (59%), and had more than five friends who visited their homes 26 (67%). While, the orphans living in institutional care homes 17(30%) had no birth certificates, fewer contacts with siblings 2 (12%), and none had friends outside the care homes. CONCLUSIONS: Kinship care is better model for psychosocial and economic security for AIDS orphans in Nepal, rather than institutional care. Families can provide good protection to AIDS orphans if government provides minimum support to them.


Subject(s)
Child, Orphaned , Foster Home Care , HIV Infections/therapy , Orphanages , Adolescent , Child , Child, Orphaned/statistics & numerical data , Cross-Sectional Studies , Female , Humans , Male , Nepal/epidemiology , Orphanages/statistics & numerical data , Psychology , Socioeconomic Factors
4.
Clin Radiol ; 67(6): 605-12, 2012 Jun.
Article in English | MEDLINE | ID: mdl-22226566

ABSTRACT

The aim of this article is to illustrate the spectrum of disease visualized at small bowel magnetic resonance imaging (MRI) in the district general hospital (DGH) setting. The advantages and disadvantages of small bowel MRI, technique, and service implementation are discussed.


Subject(s)
Hospitals, District , Intestine, Small/pathology , Magnetic Resonance Imaging/methods , Adult , Aged , Aged, 80 and over , Contrast Media , Female , Humans , Male , Middle Aged , Sensitivity and Specificity , United Kingdom , Young Adult
5.
Acta Neurochir Suppl ; 111: 145-9, 2011.
Article in English | MEDLINE | ID: mdl-21725746

ABSTRACT

The CNS inflammatory reaction occurring after aneurysmal subarachnoid hemorrhage (SAH) involves the upregulation of numerous cytokines and prostaglandins. Cyclooxygenase (COX) inhibition is a well-established pharmacological anti-inflammatory agent. Previous studies have shown marked increases in COX-2 expression in neurons, astrocytes, microglia, and endothelial cells following brain injury. COX-2 inhibition has been shown to be beneficial following various types of brain injury. This experiment investigates the role of COX-2 activity in early brain injury following SAH. CD-1 mice were subjected to an endovascular perforation model of SAH or SHAM surgery. Following experimental SAH animals were treated with the specific COX-2 inhibitor, NS398, in dosages of either 10 or 30 mg/kg. Neurological performance and brain edema were evaluated 24 and 72 h after SAH. NS398 at 30 mg/kg significantly reduced SAH-induced neurological deterioration. NS 398 at 30 mg/kg resulted in a trend toward the reduction of SAH-induced cerebral edema. Treatment had no effect on mortality. This experiment provides preliminary evidence that COX-2 inhibition is an effective pharmacological intervention for the prevention of brain edema and the preservation of neurological function following SAH.


Subject(s)
Brain Injuries/prevention & control , Cyclooxygenase 2 Inhibitors/therapeutic use , Nitrobenzenes/therapeutic use , Subarachnoid Hemorrhage/drug therapy , Sulfonamides/therapeutic use , Animals , Brain Edema/etiology , Brain Edema/prevention & control , Brain Injuries/etiology , Disease Models, Animal , Dose-Response Relationship, Drug , Male , Mice , Neurologic Examination , Subarachnoid Hemorrhage/complications , Time Factors
6.
Acta Neurochir Suppl ; 111: 283-7, 2011.
Article in English | MEDLINE | ID: mdl-21725769

ABSTRACT

Intracranial surgery causes brain damage from cortical incisions, intraoperative hemorrhage, retraction, and electrocautery; collectively these injuries have recently been coined surgical brain injury (SBI). Inflammation following SBI contributes to neuronal damage. This study develops T-cells that are immunologically tolerant to brain antigen via the exposure of myelin basic protein (MBP) to airway mucosa. We hypothesize that these T-cells will migrate to the site of corticotomy, secrete immunosuppressive cytokines, such as TGFß1, reduce inflammation, and improve neurological outcomes following SBI. A standard model for SBI was used for this experiment. C57 mice were divided into six groups: SHAM+Vehicle, SHAM+Ovalbumin, SHAM+MBP, SBI+Vehicle, SBI+OVA, and SBI+MBP. Induction of mucosal tolerance to vehicle, ovalbumin, or MBP was performed prior to SBI. Neurological scores and TBFß1 cytokine levels were measured 48 h postoperatively. Mice receiving craniotomy demonstrated a reduction in neurological score. Animals tolerized to MBP (SBI+MBP) had better postoperative neurological scores than SBI+Vehicle and SBI+OVA. SBI inhibited the cerebral expression TGFß1 in PBS and OVA treated groups, whereas MBP treated-animals preserved preoperative levels. Mucosal tolerance to MBP leads to significant improvement in neurological outcome that is associated with the preservation of endogenous levels of brain TGFß1.


Subject(s)
Brain Injuries/etiology , Brain Injuries/pathology , Craniotomy/adverse effects , Mucous Membrane/immunology , Transforming Growth Factor beta1/metabolism , Analysis of Variance , Animals , Brain/immunology , Brain/metabolism , Brain/pathology , Brain Injuries/complications , Brain Injuries/therapy , Disease Models, Animal , Drug Tolerance/immunology , Inflammation/etiology , Mice , Mice, Inbred C57BL , Mucous Membrane/drug effects , Myelin Basic Protein/immunology , Neurologic Examination , Ovalbumin/therapeutic use , Transforming Growth Factor beta1/immunology , Treatment Outcome
8.
Acta Neurochir Suppl ; 105: 99-100, 2008.
Article in English | MEDLINE | ID: mdl-19066091

ABSTRACT

Free radical scavengers have been shown to improve short-term outcome after intracerebral hemorrhage (ICH). The purpose of this study was to evaluate whether melatonin (a potent free radical scavenger and an indirect antioxidant) can improve short- and/or long-term neurological function after ICH, which was induced by collagenase injection into the striatum of adult rats. Melatonin (15 mg/kg) was administered by intraperitoneal injection at 1, 24, 48, and 72 h. Neurological and behavioral testing was performed at several time points from 1 day to 8 weeks post-ICH. Neurological and behavioral deficits were observed in ICH rats at all time points, but the melatonin treatment regimen did not improve performance or level of brain injury.


Subject(s)
Antioxidants/therapeutic use , Cerebral Hemorrhage/drug therapy , Melatonin/therapeutic use , Animals , Behavior, Animal/drug effects , Brain Infarction/drug therapy , Brain Infarction/etiology , Cerebral Hemorrhage/chemically induced , Cerebral Hemorrhage/complications , Cerebral Hemorrhage/pathology , Collagenases , Corpus Striatum/drug effects , Disease Models, Animal , Exploratory Behavior/drug effects , Male , Motor Activity/drug effects , Neurologic Examination , Rats , Rats, Sprague-Dawley , Time Factors
9.
Acta Neurochir Suppl ; 105: 179-84, 2008.
Article in English | MEDLINE | ID: mdl-19066106

ABSTRACT

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating neurological event that accounts for 3-7% of all strokes and carries a mortality rate as high as 40%. Delayed cerebral vasospasm has traditionally been recognized as the most treatable cause of morbidity and mortality from SAH. However, evidence is mounting that the physiological and cellular events of acute brain injury, which occur during the 24-72 h following aneurysm rupture, make significant contributions to patient outcomes, and may even be a more significant factor than delayed cerebral vasospasm. Acute brain injury in aneurysmal SAH is the result of physiological derangements such as increased intracranial pressure and decreased cerebral blood flow that result in global cerebral ischemia, and lead to the acute development of edema, oxidative stress, inflammation, apoptosis, and infarction. The consequence of these events is often death or significant neurological disability. In this study of acute brain injury, we elucidate some of the complex molecular signaling pathways responsible for these poor outcomes. Continued research in this area and the development of therapies to interrupt these cascades should be a major focus in the future as we continue to seek effective therapies for aneurysmal SAH.


Subject(s)
Brain Injuries/etiology , Brain Injuries/therapy , Subarachnoid Hemorrhage/complications , Animals , Brain Infarction/etiology , Cell Death , Humans , Inflammation/physiopathology , Oxidative Stress/physiology , Time Factors
10.
Acta Neurochir Suppl ; 104: 33-41, 2008.
Article in English | MEDLINE | ID: mdl-18456995

ABSTRACT

Aneurismal subarachnoid haemorrhage (SAH) is a devastating disease that is associated with significant morbidity and mortality. The mortality is approximately 50%, with 30% of survivors having significant morbidity. There is substantial evidence to suggest that oxidative stress is significant in the development of acute brain injury and cerebral vasospasm following SAH. There are several sources for the excessive generation of free radicals following SAH, including disrupted mitochondrial respiration and extracellular hemoglobin. There is also the upregulation of free radical producing enzymes such as inducible nitric oxide synthase (iNOS), xanthine oxidase, NADPH oxidase (NOX), as well as enzymes involved in the metabolism of arachidonic acid. Additionally, intrinsic antioxidant systems such as superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) are inhibited. Experiments have linked free radicals to the apoptosis of neurons and endothelial cells, BBB breakdown and the altered contractile response of cerebral vessels following SAH. Antioxidant therapy has provided neuroprotection and antispasmotic effects in experimental SAH and some therapies have demonstrated improved outcomes in clinical trials. These studies have laid a foundation for the use of antioxidants in the treatment of aneurismal SAH.


Subject(s)
Brain Injuries/physiopathology , Oxidative Stress/physiology , Subarachnoid Hemorrhage/physiopathology , Vasospasm, Intracranial/physiopathology , Brain Injuries/etiology , Brain Injuries/mortality , Free Radicals/metabolism , Humans , Mitochondria/physiology , Oxyhemoglobins/metabolism , Subarachnoid Hemorrhage/mortality
11.
Acta Neurochir Suppl ; 104: 287-90, 2008.
Article in English | MEDLINE | ID: mdl-18457003

ABSTRACT

3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors, commonly known as statins, are widely used clinically for their lipid lowering properties. Recent evidence shows that statins are also effective in ameliorating cerebral vasospasm, which occurs as sequelae of subarachnoid haemorrhage. This review focuses on the pleiotropic effects of statins, and the putative mechanisms involved in statin mediated attenuation of cerebral vasospasm.


Subject(s)
Hydroxymethylglutaryl-CoA Reductase Inhibitors/therapeutic use , Vasospasm, Intracranial/drug therapy , Animals , Disease Models, Animal , Muscle, Smooth, Vascular/enzymology , Nitric Oxide Synthase Type III/genetics , Subarachnoid Hemorrhage/drug therapy
12.
BMC Musculoskelet Disord ; 6: 13, 2005 Mar 09.
Article in English | MEDLINE | ID: mdl-15757518

ABSTRACT

BACKGROUND: There is paucity of literature describing complex elbow trauma in the pediatric population. We described a case of an uncommon pediatric elbow injury comprised of lateral condyle fracture associated with posterolateral dislocation of elbow. CASE PRESENTATION: A 12-year-old boy sustained a direct elbow trauma and presented with Milch type II lateral condyle fracture associated with posterolateral dislocation of elbow. Elbow dislocation was managed by closed reduction. The elbow stability was assessed under general anaesthesia, followed by open K-wiring for the lateral condylar fracture fixation. The patient had an uneventful recovery with an excellent outcome at 39 months follow-up. CONCLUSION: Complex pediatric elbow injuries are quite unusual to encounter, the management of such fractures can be technically demanding. Concomitant elbow dislocation should be managed by closed reduction followed by open reduction and internal fixation (K-wires or cannulated screws) of the lateral condyle fracture.


Subject(s)
Bone Wires , Elbow Injuries , Fracture Fixation, Internal/methods , Fractures, Bone/surgery , Joint Dislocations/therapy , Child , Elbow Joint/diagnostic imaging , Fractures, Bone/diagnostic imaging , Humans , Joint Dislocations/diagnostic imaging , Male , Radiography
13.
Biophys J ; 77(6): 3384-93, 1999 Dec.
Article in English | MEDLINE | ID: mdl-10585961

ABSTRACT

The effect of Mg(2+) on the process of Ca(2+) release from the caged Ca(2+) compound DM-nitrophen (NP) was studied in vitro by steady light UV photolysis of NP in the presence of Ca(2+) and Mg(2+). Ca(2+) release during photolysis and its relaxation/recovery after photolysis were monitored with the Ca(2+)-sensitive dye fura-2. Mg(2+) speeds the photorelease of Ca(2+) during photolysis and slows the relaxation of Ca(2+) to new steady-state levels after photolysis. Within the context of a model describing NP photolysis, we determined the on and off rates of Mg(2+) binding to unphotolyzed NP (k(on) = 6.0 x 10(4) M(-1) s(-1); k(off) = 1.5 x 10(-1) s(-1)). Furthermore, to fully account for the slow postphotolysis kinetics of Ca(2+) in the presence of Mg(2+) we were forced to add an additional photoproduct to the standard model of NP photolysis. The additional photoproduct is calculated to have a Ca(2+) affinity of 13.3 microM and is hypothesized to be produced by the photolysis of free or Mg(2+)-bound NP; photolysis of Ca(2+)-bound NP produces the previously documented 3 mM Ca(2+) affinity photoproduct.


Subject(s)
Acetates/metabolism , Calcium/metabolism , Ethylenediamines/metabolism , Magnesium/metabolism , Acetates/radiation effects , Biophysical Phenomena , Biophysics , Chelating Agents/metabolism , Chelating Agents/radiation effects , Ethylenediamines/radiation effects , Fluorescent Dyes , Fura-2 , In Vitro Techniques , Kinetics , Models, Biological , Photochemistry , Photolysis , Ultraviolet Rays
14.
J Membr Biol ; 157(3): 215-30, 1997 Jun 01.
Article in English | MEDLINE | ID: mdl-9178609

ABSTRACT

Many mutations that shift the voltage dependence of activation in Shaker channels cause a parallel shift of inactivation. The I2 mutation (L382I in the Shaker B sequence) is an exception, causing a 45 mV activation shift with only a 9 mV shift of inactivation midpoint relative to the wildtype (WT) channel. We compare the behavior of WT and I2 Shaker 29-4 channels in macropatch recordings from Xenopus oocytes. The behavior of WT channels can be described by both simple and detailed kinetic models which assume that inactivation proceeds only from the open state. The behavior of I2 channels requires that they inactivate from closed states as well, a property characteristic of voltage-gated sodium channels. A detailed "multiple-state inactivation" model is presented that describes both activation and inactivation of I2 channels. The results are consistent with the view that residue L382 is associated with the receptor for the inactivation particles in Shaker channels.


Subject(s)
Ion Channel Gating/genetics , Potassium Channels/genetics , Animals , Drosophila , Drosophila Proteins , Mutation , Patch-Clamp Techniques , Potassium Channels/metabolism , Shaker Superfamily of Potassium Channels , Xenopus
15.
J Neurobiol ; 23(8): 965-82, 1992 Oct.
Article in English | MEDLINE | ID: mdl-1460467

ABSTRACT

This article provides characterization of the electrical response to odorants in the Drosophila antenna and provides physiological evidence that a second organ, the maxillary palp, also has olfactory function in Drosophila. The acj6 mutation, previously isolated by virtue of defective olfactory behavior, affects olfactory physiology in the maxillary palp as well as in the antenna. Interestingly, abnormal chemosensory jump 6 (acj6) reduces response in the maxillary palp to all odorants tested except benzaldehyde (odor of almond), as if response to benzaldehyde is mediated through a different type of odorant pathway from the other odorants. In other experiments, different parts of the antenna are shown to differ with respect to odorant sensitivity. Evidence is also provided that antennal response to odorants varies with age, and that odorants differ in their age dependence.


Subject(s)
Drosophila/physiology , Olfactory Pathways/physiology , Sense Organs/physiology , Smell/physiology , Animals , Electrodes , Electrophysiology , Female , Male , Microscopy, Electron, Scanning , Mutation , Odorants , Olfactory Pathways/growth & development , Sense Organs/anatomy & histology , Sex Characteristics
16.
Proc Natl Acad Sci U S A ; 88(12): 5467-71, 1991 Jun 15.
Article in English | MEDLINE | ID: mdl-1905022

ABSTRACT

Mutations affecting olfactory behavior provide material for use in molecular studies of olfaction in Drosophila melanogaster. Using the electroantennogram (EAG), a measure of antennal physiology, we have found an adult antennal defect in the olfactory behavioral mutant abnormal chemosensory jump 6 (acj6). The acj6 EAG defect was mapped to a single locus and the same mutation was found to be responsible for both reduction in EAG amplitude and diminished behavioral response, as if reduced antennal responsiveness to odorant is responsible for abnormal chemosensory behavior in the mutant. acj6 larval olfactory behavior is also abnormal; the mutation seems to alter cellular processes necessary for olfaction at both developmental stages. The acj6 mutation exhibits specificity in that visual system function appears normal in larvae and adults. These experiments provide evidence that the acj6 gene encodes a product required for olfactory signal transduction.


Subject(s)
Drosophila melanogaster/genetics , Genes , Olfactory Bulb/physiology , Animals , Behavior, Animal , Chromosome Mapping , Electrophysiology , Mutation , Recombination, Genetic
17.
J Electron Microsc Tech ; 13(1): 16-26, 1989 Sep.
Article in English | MEDLINE | ID: mdl-2674366

ABSTRACT

The ability to obtain diffraction patterns with a large angular view has significantly enhanced the ease and potential of electron diffraction studies in the determination of unit cells and identification of submicron phases. Convergent beam electron diffraction (CBED) provides a two-dimensional projection of the three-dimensional reciprocal lattice and can be utilized to reconstruct the unit cell dimensions. In particular, the spacing of the reciprocal lattice layers parallel to the electron beam and the location and distribution of the reflections in the first and higher order Laue zones with respect to the zero layer provide information which cannot be obtained from the zero layer pattern alone. This additional information permits the identification of crystal structures of phases under investigation with previously established ones or the determination of a new structure, if previously unknown. The article describes the principles of the analysis and illustrates the application of the methods with examples from commercial material systems.


Subject(s)
Crystallography/methods , Microscopy, Electron , Electrons , Microscopy, Electron/methods
18.
Behav Genet ; 19(2): 267-83, 1989 Mar.
Article in English | MEDLINE | ID: mdl-2497723

ABSTRACT

Drosophila larvae are attracted to a wide variety of chemical stimuli. The olfactory response to ethyl acetate, a powerful attractant, was found to be surprisingly well conserved across a variety of different wild-type strains. Strain differences are documented, however, both in attraction to ethyl acetate and in another chemosensory behavior: avoidance of an aversive stimulus. As a means of analyzing the extent of genetic heterogeneity within strains, one wild-type population, Canton-S, was screened for variant X chromosomes. An enrichment procedure was characterized and used to make the screening more efficient. Lines homozygous for individual X chromosomes were established, and all were found to exhibit a strong olfactory response, although evidence was found for variation among them. The olfactory response was found to be conserved through an extended period of larval development, including the final period during which larvae leave the culture medium in preparation for metamorphosis. The results are discussed in terms of the genetic basis of the response and the use of single-gene mutations as a means of dissecting olfactory system function.


Subject(s)
Drosophila melanogaster/genetics , Smell/physiology , Animals , Chemoreceptor Cells/physiology , Female , Genetic Carrier Screening , Genetic Linkage , Larva/genetics , Male , Mutation
19.
J Membr Biol ; 101(3): 209-23, 1988 Mar.
Article in English | MEDLINE | ID: mdl-2455058

ABSTRACT

Single ventricle cells were dissociated from the hearts of two-, three-, four- or seven-day-old chick embryos, and were maintained in vitro for an additional 6 to 28 hr. Rounded 13 to 18 micron cells with input capacitance of 5 to 10 pF were selected for analysis of fast sodium current (INa). Voltage command protocols designed to investigate the magnitude, voltage dependence, and kinetics of INa were applied with patch electrodes in the whole-cell clamp configuration. INa was present in over half of the 2d, and all 3d, 4d and 7d cells selected. The current showed no systematic differences in activation kinetics, voltage dependence, or tetrodotoxin (TTX) sensitivity with age or culture conditions. Between the 2d and 7d stages, the rate of current inactivation doubled and channel density increased about eightfold. At all stages tested, INa was blocked by TTX at a half-effective concentration of 0.5 to 1.0 nM. We conclude that the lack of Na dependence of the action potential upstroke on the second day of development results from the relatively depolarized level of the diastolic potential, and failure to activate the small available excitatory Na current. The change from Ca to Na dependence of the upstroke during the third to the seventh day of incubation results partly from the negative shift of the diastolic potential during this period, and in part from the increase in available Na conductance.


Subject(s)
Ion Channels/metabolism , Myocardium/metabolism , Sodium/metabolism , Action Potentials/drug effects , Animals , Calcium/metabolism , Chick Embryo , In Vitro Techniques , Ion Channels/drug effects , Myocardium/cytology , Tetrodotoxin/pharmacology
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