Development of a Home-Based Telerehabilitation Service Delivery Protocol for Wheelchair Seating and Mobility Within the Veterans Health Administration.

INTRODUCTION: The provision of seating and wheeled mobility devices is a complex process that requires trained professionals and multiple appointments throughout the service delivery process. However, this can be inconvenient and burdensome for individuals with mobility limitations or for individuals who live in rural areas. Rural areas often present unique difficulties regarding the provision of healthcare services including lengthy travel times to medical facilities and lack of specialized providers and medical technology. The purpose of this article is to provide a comprehensive overview of the development and implementation of a service delivery protocol for a home-based telerehabilitation assessment for wheelchair seating and mobility. MATERIALS AND METHODS: The telerehabilitation team consists of a trained wheelchair seating and mobility therapist and a telehealth clinical technician (TCT). In order to determine veterans that are appropriate for a home-based telerehabilitation assessment, a three-phase pre-assessment screening process was conducted by the therapist and TCT, including consult, chart, and phone review. Veterans that met all of the predetermined eligibility criteria were recommended for a telerehabilitation wheelchair assessment. The TCT traveled to the veteran's residence with necessary evaluation and safety equipment and connected with the therapist remotely using the VA Video Connect platform. Assessment and veteran data were collected during the initial evaluation and then during a 21-day follow-up. RESULTS: Forty-three veterans were successfully seen via telerehabilitation for a seating and wheeled mobility assessment between November, 2017 and July, 2018. The average travel distance between the veteran's residence and the clinic was 34.1 miles. The total telerehabilitation encounter times ranged from 45 min to 145 min. CONCLUSIONS: The implementation of this service delivery protocol for wheelchair seating and mobility assessments demonstrated the benefits of using telehealth services including reaching rural veterans, reducing distance traveled, maximizing efficiency of provider schedules, and conducting realistic assessments in veterans' home environments. Success can be attributed to being able to deliver best practice remotely and to the rapport of the TCT with the providers. Cultivating provider buy-in, selecting appropriate outcome measures, and restructuring workflows were additional lessons learned. The VA Video Connect platform is an accessible tool that can be easily learned by both veterans and providers and used beyond initial wheelchair seating evaluations for improved access to follow-up healthcare services.

Veteran and Provider Satisfaction with a Home-Based Telerehabilitation Assessment for Wheelchair Seating and Mobility.

The objective of this project was to measure Veteran and provider satisfaction with a home-based telerehabilitation assessment for wheelchair seating and mobility. Forty-three Veterans were seen remotely at their place of residence by a provider, using a VA Video Connect synchronous videoconferencing system. Veteran and provider satisfaction were collected using the Telerehabilitation Questionnaire (TRQ). Mean individual TRQ scores for both Veterans and providers were significantly higher than the scale midpoint of 3.5. Veterans had higher scores than providers for five individual items on the TRQ. Higher scores by Veterans on the technology and quality and clarity of the video and audio likely correspond to the differences in environmental settings in which the visit occurred for the Veteran compared with the provider. High satisfaction scores with the telerehabilitation assessments are likely attributed to the positive working relationship between the provider and the rehabilitation technician, who provided in-person technical support to the Veteran in the home during the wheeled mobility evaluation. Overall, the results indicate a high level of Veteran and provider satisfaction using telerehabilitation for wheelchair seating and mobility evaluations.

Survival and variability over time from out of hospital cardiac arrest across large geographically diverse communities participating in the Resuscitation Outcomes Consortium.

BACKGROUND: The Resuscitation Outcomes Consortium (ROC)epidemiological registry (Epistry) provides opportunities to assess trends in out-of-hospital cardiac arrest treatment and outcomes. METHODS: Patient, event, system, treatment, and outcome data from adult (≥18 years) out-of-hospital cardiac arrest (OHCA) from 10 geographically diverse North American ROC sites over four 12-month epochs, from July 1, 2011 to June 30, 2015, were assessed. Descriptive statistics were used to characterize the sample and logistic regression assessed the association of study epoch and key covariates on survival. RESULTS: Overall, 85,553 patients were assessed by Emergency Medical Services (EMS) and 45,516 (53.2%, site range 30.4%-69.9%) had resuscitation attempted by EMS. Patient and event characteristics were consistent except for increases in bystander CPR (41.3%-44.9%) and bystander AED application (3.9%-5.2%). EMS CPR depth and compression fraction increased while pre-shock pause interval decreased. Targeted temperature management was performed in 51.1% of admitted patients and early coronary angiography in 30.2%. Survival to hospital discharge improved (from 10.9% to 11.3% across epochs) with epoch significantly associated with survival (p < 0.001) showing an increasing trend in survival over time. (p = 0.02). Marked site variation in survival persisted within and across epochs (overall site range: 4.2%-19.8%). Patients with an initially shockable rhythm (VT/VF) had an overall survival of 32.2% (site range: 11.9%-47.1%) while survival in bystander witnessed VT/VF was 35.8% (site range: 12.9%-53.1%). CONCLUSIONS: Survival from adult OHCA in multiple large geographically-separate sites improved over the study period. Marked site differences in survival persist and addressing this variation is essential to improve outcomes from OHCA across North America.

General anaesthetics do not impair developmental expression of the KCC2 potassium-chloride cotransporter in neonatal rats during the brain growth spurt.

BACKGROUND: The developmental transition from depolarizing to hyperpolarizing γ-aminobutyric acid-mediated neurotransmission is primarily mediated by an increase in the amount of the potassium-chloride cotransporter KCC2 during early postnatal life. However, it is not known whether early neuronal activity plays a modulatory role in the expression of total KCC2 mRNA and protein in the immature brain. As general anaesthetics are powerful modulators of neuronal activity, the purpose of this study was to explore how these drugs affect KCC2 expression during the brain growth spurt. METHODS: Wistar rat pups were exposed to either a single dose or 6 h of midazolam, propofol, or ketamine anaesthesia at postnatal days 0, 5, 10, or 15. KCC2 expression was assessed using immunoblotting, immunohistochemistry, or quantitative polymerase chain reaction analysis up to 3 days post-exposure in the medial prefrontal cortex. RESULTS: There was a progressive and steep increase in the expression of KCC2 between birth and 2 weeks of age. Exposure to midazolam, propofol, or ketamine up to 6 h at any investigated stages of the brain growth spurt did not influence the expression of this cotransporter protein. CONCLUSION: I.V. general anaesthetics do not seem to influence developmental expression of KCC2 during the brain growth spurt.

Relationship between neuronal vulnerability and potassium-chloride cotransporter 2 immunoreactivity in hippocampus following transient forebrain ischemia.

Cation chloride cotransporters have been reported to be expressed in neurons in the hippocampus and to regulate intracellular Cl(-) concentration. The neuron-specific K-Cl cotransporter 2 (KCC2) is necessary for maintaining the low intracellular chloride concentration required for the hyperpolarizing actions of GABA. In this study we examined the vulnerability of KCC2-containing neurons as well as the changes in the pattern of KCC2 distribution in the rat hippocampus following 15 min ischemia induced by four-vessel occlusion. Immunostaining for the 72 kDa heat shock protein (HSP-72) was used to investigate the extent of damage in neuronal populations previously shown to be vulnerable to ischemia. At 6-24 h after ischemia, when the pyramidal cells in the CA1 (subfield of cornu Ammonis) region showed no morphological signs of damage, a small rise of KCC2 immunoreactivity was already observed. After 2 days, when the CA1 pyramidal cells started to degenerate, a progressive downregulation of the KCC2 protein was visible. Interestingly, in the same areas, the parvalbumin containing interneurons showed no signs of ischemic damage, and KCC2 immunoreactivity was retained on their membrane surface. In CA1 pyramidal cells, the reduction in KCC2 expression may lead to an elevation of intracellular Cl(-) concentration, which causes a shift in equilibrium potential toward more positive levels. Consequently, the reduction of the inhibitory action of GABA through downregulation of KCC2 function may be involved in the pathomechanisms of delayed neuronal death in the CA1 subfield.

Muscle fiber type I influences lipid oxidation during low-intensity exercise in moderately active middle-aged men.

The simultaneous effects of body composition, cardiorespiratory fitness, physical activity, and muscle fiber characteristics on lipid oxidation at basal state and during exercise were studied in a population-based group (n = 70) of middle-aged men. Body composition, oxygen uptake, and lipid oxidation were determined in a volitional maximal exercise test, physical activity with a questionnaire, muscle fiber characteristics with muscle biopsy, and resting metabolic rate and lipid oxidation at basal state with indirect calorimetry. In regression analysis, type I muscle fibers contributed significantly to lipid oxidation at basal state (r = 0.30, r2 = 0.07, P<0.05) and during low-intensity exercise (r = 0.35, r2 = 0.10, P<0.05). ANOVA revealed 7.7% (P = 0.268) lower lipid oxidation at basal state, 14% (P<0.05) lower lipid oxidation in low-intensity exercise, and 10.5% (P = 0.088) lower lipid oxidation in moderate-intensity exercise in muscle fiber tertile I (type I muscle fiber count 28.8%) compared with muscle fiber tertile III (type I muscle fiber count 71.4%). In conclusion, the muscle fiber distribution contributed significantly to lipid oxidation during low-intensity exercise in moderately active middle-aged men.

Evaluation of commercially available electrodes and gels for recording of slow EEG potentials.

OBJECTIVE: To test the applicability of different types of commercially available electrodes and electrode gels or pastes for recording of slow EEG potentials. METHODS: Experiments were carried out on six types of reusable electrodes (silver, tin and gold cup electrodes, sintered silver-silver chloride (Ag|AgCl), platinum, stainless steel), six disposable Ag|AgCl electrode models, and nine gels or pastes. We studied the parameters, which are critical in slow-potential recording, such as polarization, initial and long-term stability and low-frequency noise. RESULTS: The best results were obtained with the reusable sintered Ag|AgCl electrodes. The six disposable Ag|AgCl electrode models also proved to have appropriate electrical properties. Other types of reusable electrodes suffered from diverse degrees of polarization, baseline drift, low-frequency noise, high resistance, and changes in properties due to wear and tear. Seven out of nine gels or pastes contained a significant amount of chloride, which is a prerequisite for DC stability of Ag|AgCl electrodes, whereas the absolute concentration of chloride had little effect. CONCLUSIONS: Direct current (DC) coupled recording of EEG is critically dependent on the choice of electrode and gel. SIGNIFICANCE: Our results provide rigorous criteria for choosing DC-stable electrodes and gels for DC-coupled or long time-constant AC-coupled recordings of slow EEG potentials.

Organic matter balance in ECF kraft mill fiberline.

Organic matter balances of an ECF kraft mill fiberline were studied in three different operational conditions of the oxygen delignification stage by implementing mill measurements, collecting routine mill data and combining them in a modified PROCELL steady state model. Dissolved volatile solids was the basic measurement for organic matter in liquid streams. Normal operation of the O2D0E(O)D1E(OP)D2 fiberline was described successfully. It was also possible to describe exceptional operating situations in the oxygen delignification stage and their effects on other parts of the production process reasonably well in order to focus studies on aspects requiring further attention. The existence of organic matter lost through complete degradation and volatile organic compounds in unit processes as well as its sensitivity to yield and operational situations is shown. The different perspectives of pulp production and wastewater treatment can be brought closer to each other using the approach in this study. The variation in the fractions discharged to wastewater treatment, although a relatively small share of the overall organic matter balance, will continue to become more important also for pulp production when effluent streams are increasingly turned back to the production line through further closure. Studies like the one presented here, can contribute to the evaluation of this development.

Degradation of EDTA and DTPA in chlorine dioxide bleaching conditions.

The decomposition of EDTA and DTPA was studied in simulated chlorine dioxide bleaching conditions. Under the investigated conditions EDTA and DTPA decomposed readily. Accordingly, feeding the chelating agents to the first chlorine dioxide stages (D0) should be reconsidered, when successful metal removal is desired. On the other hand, chlorine dioxide water may be utilized to degrade the chelating agents.

Infraslow oscillations modulate excitability and interictal epileptic activity in the human cortex during sleep.

Human cortical activity has been intensively examined at frequencies ranging from 0.5 Hz to several hundred Hz. Recent studies have, however, reported also infraslow fluctuations in neuronal population activity, magnitude of electroencephalographic oscillations, discrete sleep events, as well as in the occurrence of interictal events. Here we use direct current electroencephalography to demonstrate large-scale infraslow oscillations in the human cortex at frequencies ranging from 0.02 to 0.2 Hz. These oscillations, which are not detectable in conventional electroencephalography because of its limited recording bandwidth (typical lower limit 0.5 Hz), were observed in widespread cortical regions. Notably, the infraslow oscillations were strongly synchronized with faster activities, as well as with the interictal epileptic events and K complexes. Our findings suggest that the infraslow oscillations represent a slow, cyclic modulation of cortical gross excitability, providing also a putative mechanism for the as yet enigmatic aggravation of epileptic activity during sleep.

Scalp-recorded slow EEG responses generated in response to hemodynamic changes in the human brain.

OBJECTIVE: To study whether hemodynamic changes in human brain generate scalp-EEG responses. METHODS: Direct current EEG (DC-EEG) was recorded from 12 subjects during 5 non-invasive manipulations that affect intracranial hemodynamics by different mechanisms: bilateral jugular vein compression (JVC), head-up tilt (HUT), head-down tilt (HDT), Valsalva maneuver (VM), and Mueller maneuver (MM). DC shifts were compared to changes in cerebral blood volume (CBV) measured by near-infrared spectroscopy (NIRS). RESULTS: DC shifts were observed during all manipulations with highest amplitudes (up to 250 microV) at the midline electrodes, and the most pronounced changes (up to 15 microV/cm) in the DC voltage gradient around vertex. In spite of inter-individual variation in both amplitude and polarity, the DC shifts were consistent and reproducible for each subject and they showed a clear temporal correlation with changes in CBV. CONCLUSIONS: Our results indicate that hemodynamic changes in human brain are associated with marked DC shifts that cannot be accounted for by intracortical neuronal or glial currents. Instead, the data are consistent with a non-neuronal generator mechanism that is associated with the blood-brain barrier. SIGNIFICANCE: These findings have direct implications for mechanistic interpretation of slow EEG responses in various experimental paradigms.

The role of organic matter lost in kraft pulping material balances .

Efficiency improvement in a pulp mill includes minimisation of environmental discharges simultaneously with the development of pulp quality and production economy. Material balances in production processes, including fate of sidestreams, are key in proceeding these matters. Different approaches of determining the material balances increase understanding of process behaviour. We have focused on measuring sidestream (carryovers, washing water, filtrate) dissolved organic matter (DOM) in fibreline unit process blocks of softwood ECF bleached kraft production. The DOM was analysed by traditional wastewater methods (volatile solids, organic carbon, chemical oxygen demand). The measured data was combined with primarily simulated water balances and routine operational mill data in a simulation model. From this balance, yield estimate included, lost organic matter through complete degradation (CD) and volatile organic compounds (VOC) can be calculated throughout the fibreline. The sensitivity of this considerable amount (23-35 kgDVS/adt in total) to various factors is discussed in this paper.

Very slow EEG responses lateralize temporal lobe seizures: an evaluation of non-invasive DC-EEG.

BACKGROUND: This study tested the idea that very slow EEG responses (direct current [DC] potential shifts) could be detected noninvasively during temporal lobe (TL) seizures, and that these shifts give lateralizing information consistent with that obtained by other methods. METHODS: Seven patients with TL epilepsy (TLE) were recorded with scalp DC-EEG technique at bedside. All recordings were performed simultaneously with conventional EEG (scalp in five, and intracranially in two; two patients with scalp recordings were recorded intracranially later). Seizures in five patients originated in the mesial TL. Ictal DC shifts were evaluated by comparing them to the temporal evolution of ictal discharges, and by comparing the laterality of these shifts to the side of seizure onset defined by routine EEG and other presurgical diagnostic tests. RESULTS: All seizures (35/35) were associated with negative DC shifts at temporal derivations (30 to 150 micro V relative to vertex), beginning at the electrical seizure onset, and lasting for the whole seizure. In eight seizures (five patients) with documented mesial TL onset, the polarity of the DC shift was initially positive followed by a negative one after lateral spread of seizure activity. In all cases, the side of the EEG shift agreed with other diagnostic tests, and, at times, was more clearly lateralized than the conventional scalp EEG. CONCLUSIONS: DC-EEG recordings are practical and achievable at the bedside. Ictal DC shifts are consistently observed in scalp recordings in TL seizures, and reliably lateralize them. This method may hold promise in reducing the need for invasive monitoring in patients with TLE where other noninvasive tests are equivocal.

DC-EEG discloses prominent, very slow activity patterns during sleep in preterm infants.

OBJECTIVES: The objective of this study is to test the hypothesis that the immature human brain exhibits slow electrical activity that is not detected by conventional (i.e. high-pass filtered) electroencephalography (EEG). METHODS: Six healthy preterm infants (conceptional age 33-37 weeks) were recorded bedside with direct current (DC) EEG during sleep. Epochs with quiet sleep were selected to study the delta frequency bursts during discontinuous EEG patterns (trace discontinu or trace alternant), and we compared the waveforms obtained without filtering (i.e. genuine DC-EEG) to those seen after high pass filtering of the same traces. RESULTS: In all infants, DC-EEG demonstrated that the typical delta frequency bursts are consistently embedded in very large amplitude (200-700 microV) and long lasting (1-5s) occipitally negative transients, which are not seen in conventional EEG. CONCLUSIONS AND SIGNIFICANCE: Our study demonstrates that (i) the most prominent spontaneous EEG activity of a sleeping preterm infant consists of very slow, large amplitude transients, and (ii) the most salient features of these transients are not seen in conventional EEG. Proper recording of this type of brain activity by DC-EEG provides a novel way for non-invasive assessment of neonatal brain function.

Post-insult activity is a major cause of delayed neuronal death in organotypic hippocampal slices exposed to glutamate.

We investigated the pathophysiological mechanisms of glutamate-induced delayed neuronal damage in rat hippocampal slice cultures [Stoppini et al. (1991) J. Neurosci. Methods 37, 173-182], with propidium iodide as a marker of cell death. Exposure of the cultures to growth medium containing 10 mM glutamate for 30 min resulted in a slowly developing degeneration of hippocampal principal cells, starting from the medial end of the CA1 region and reaching the dentate gyrus by 48 h. By 24 h, most pyramidal cells in CA1 were damaged. An acute phase of degeneration preceded the delayed damage at 2-6 h, affecting cells in a spatially diffuse manner. When tetrodotoxin (0.5 microM) was present during the glutamate insult, a marked protection (mean 57%, P<0.001) of the CA1 damage was observed. Rather strikingly, when tetrodotoxin was applied immediately following or even with a delay of 30 min after the insult, a similar amount of protection was achieved. In field recordings carried out after the insult, the glutamate-treated slices exhibited spontaneously occurring negative shifts with a duration of 1-10 s and an amplitude of up to 400 microV in the CA3 region, whereas the control slices were always quiescent. Taken together, the results suggest that post-insult neuronal network activity, rather than the direct action of exogenous glutamate, is a major cause of delayed CA1 pyramidal cell death in the organotypic slices. These observations may have implications in the design of neuroprotective strategies for the treatment of brain traumas which are accompanied by delayed and/or distal neuronal damage.

The KCl cotransporter, KCC2, is highly expressed in the vicinity of excitatory synapses in the rat hippocampus.

Immunocytochemical visualization of the neuron-specific K+/Cl- cotransporter, KCC2, at the cellular and subcellular level revealed an area- and layer-specific diffuse labelling, and a discrete staining outlining the somata and dendrites of some interneurons in all areas of the rat hippocampus. KCC2 was highly expressed in parvalbumin-containing interneurons, as well as in subsets of calbindin, calretinin and metabotropic glutamate receptor 1a-immunoreactive interneurons. During the first 2 postnatal weeks, an increase of KCC2 staining was observed in the molecular layer of the dentate gyrus, correlating temporally with the arrival of entorhinal cortical inputs. Subcellular localization demonstrated KCC2 in the plasma membranes. Immunoreactivity in principal cells was responsible for the diffuse staining found in the neuropil. In these cells, KCC2 was detected primarily in dendritic spine heads, at the origin of spines and, at a much lower level on the somata and dendritic shafts. KCC2 expression was considerably higher in the somata and dendrites of interneurons, most notably of parvalbumin-containing cells, as well as in the thorny excrescences of CA3 pyramidal cells and in the spines of spiny hilar and stratum lucidum interneurons. The data indicate that KCC2 is highly expressed in the vicinity of excitatory inputs in the hippocampus, perhaps in close association with extrasynaptic GABAA receptors. A high level of excitation is known to lead to a simultaneous net influx of Na+ and Cl-, as evidenced by dendritic swelling. KCC2 located in the same microenvironment may provide a Cl- extrusion mechanism to deal with both ion and water homeostasis in addition to its role in setting the driving force of Cl- currents involved in fast postsynaptic inhibition.

Enhanced temporal stability of cholinergic hippocampal gamma oscillations following respiratory alkalosis in vitro.

The decrease in brain CO(2) partial pressure (pCO(2)) that takes place both during voluntary and during pathological hyperventilation is known to induce gross alterations in cortical functions that lead to subjective sensations and altered states of consciousness. The mechanisms that mediate the effects of the decrease in pCO(2) at the neuronal network level are largely unexplored. In the present work, the modulation of gamma oscillations by hypocapnia was studied in rat hippocampal slices. Field potential oscillations were induced by the cholinergic agonist carbachol under an N-methyl-D-aspartate (NMDA)-receptor blockade and were recorded in the dendritic layer of the CA3 region with parallel measurements of changes in interstitial and intraneuronal pH (pH(o) and pH(i), respectively). Hypocapnia from 5 to 1% CO(2) led to a stable monophasic increase of 0.5 and 0.2 units in pH(o) and pH(i), respectively. The mean oscillation frequency increased slightly but significantly from 32 to 34 Hz and the mean gamma-band amplitude (20 to 80 Hz) decreased by 20%. Hypocapnia induced a dramatic enhancement of the temporal stability of the oscillations, as was indicated by a two-fold increase in the exponential decay time constant fitted to the autocorrelogram. A rise in pH(i) evoked by the weak base trimethylamine (TriMA) was associated with a slight increase in oscillation frequency (37 to 39 Hz) and a decrease in amplitude (30%). Temporal stability, on the other hand, was decreased by TriMA, which suggests that its enhancement in 1% CO(2) was related to the rise in pH(o). In 1% CO(2), the decay-time constant of the evoked monosynaptic pyramidal inhibitory postsynaptic current (IPSC) was unaltered but its amplitude was enhanced. This increase in IPSC amplitude seems to significantly contribute to the enhancement of temporal stability because the enhancement was almost fully reversed by a low concentration of bicuculline. These results suggest that changes in brain pCO(2) can have a strong influence on the temporal modulation of gamma rhythms.

Extracellular carbonic anhydrase activity facilitates lactic acid transport in rat skeletal muscle fibres.

1. In skeletal muscle an extracellular sarcolemmal carbonic anhydrase (CA) has been demonstrated. We speculate that this CA accelerates the interstitial CO2/HCO3- buffer system so that H+ ions can be rapidly delivered or buffered in the interstitial fluid. Because > 80 % of the lactate which crosses the sarcolemmal membrane is transported by the H+-lactate cotransporter, we examined the contributions of extracellular and intracellular CA to lactic acid transport, using ion-selective microelectrodes for measurements of intracellular pH (pHi) and fibre surface pH (pHs) in rat extensor digitorum longus (EDL) and soleus fibres. 2. Muscle fibres were exposed to 20 mM sodium lactate in the absence and presence of the CA inhibitors benzolamide (BZ), acetazolamide (AZ), chlorzolamide (CZ) and ethoxzolamide (EZ). The initial slopes (dpHs/dt, dpHi/dt) and the amplitudes (DeltapHs, DeltapHi) of pH changes were quantified. From dpHi/dt, DeltapHi and the total buffer factor (BFtot) the lactate fluxes (mM min-1) and intracellular lactate concentrations ([lactate]i) were estimated. 3. BFtot was obtained as the sum of the non-HCO3- buffer factor (BFnon-HCO3) and the HCO3- buffer factor (BFHCO3). BFnon-HCO3 was 35 +/- 4 mM pH-1 for the EDL (n = 14) and 86 /- 16 mM pH-1 for the soleus (n = 14). 4. In soleus, 10 mM cinnamate inhibited lactate influx by 44 % and efflux by 30 %; in EDL, it inhibited lactate influx by 37 % and efflux by 20 %. Cinnamate decreased [lactate]i, in soleus by 36 % and in EDL by 45 %. In soleus, 1 mM DIDS reduced lactate influx by 18 % and efflux by 16 %. In EDL, DIDS lowered the influx by 27 % but had almost no effect on efflux. DIDS reduced [lactate]i by 20 % in soleus and by 26 % in EDL. 5. BZ (0.01 mM) and AZ (0.1 mM), which inhibit only the extracellular sarcolemmal CA, led to a significant increase in dpHs/dt and pHs by about 40 %-150 % in soleus and EDL. BZ and AZ inhibited the influx and efflux of lactate by 25 %-50 % and reduced [lactate]i by about 40 %. The membrane-permeable CA inhibitors CZ (0.5 mM) and EZ (0.1 mM), which inhibit the extracellular as well as the intracellular CAs, exerted no greater effects than the poorly permeable inhibitors BZ and AZ did. 6. In soleus, 10 mM cinnamate inhibited the lactate influx by 47 %. Addition of 0.01 mM BZ led to a further inhibition by only 10 %. BZ alone reduced the influx by 37 %. 7. BZ (0.01 mM) had no influence on the Km value of the lactate transport, but led to a decrease in maximal transport rate (Vmax). In EDL, BZ reduced Vmax by 50 % and in soleus by about 25 %. 8. We conclude that the extracellular sarcolemmal CA plays an important role in lactic acid transport, while internal CA has no effect, a difference most likely attributable to the high internal vs. low extracellular BF(non-HCO3). The fact that the effects of cinnamate and BZ are not additive indicates that the two inhibitors act at distinct sites on the same transport pathway for lactic acid.

Different sensitivities of human and rat rho(1) GABA receptors to extracellular pH.

We have examined the sensitivity of human and rat homo-oligomeric rho(1) GABA receptors to variations in extracellular pH (pH(o)) using the whole-cell patch clamp technique. The GABA-induced conductance mediated by the rat rho(1) receptor (rho(1)-R) decreased with a decrease in pH(o) between 9.0 to 5.4. Below pH(o) 7.4 the effect of protons on the GABA-induced conductance was apparently competitive, but above pH(o) 7.4 the inhibitory effect of extracellular protons was almost independent on the GABA concentration. Titration of the GABA-induced conductance at 3 microM GABA revealed two protonation sites on rat rho(1)-R with pKa 6.4 and pKa 8.2. At 10 microM GABA the low pKa (6.4) was shifted to a clearly lower value (5.6), but the high pKa was only slightly decreased (from 8.2 to 7.9). Zn(2+) ions were capable of relieving the proton inhibition at low pH(o) indicating that Zn(2+) interacts with the low pKa site. Unlike the rat rho(1)-R, the human rho(1)-R was sensitive only to changes in pH(o) at acidic levels. Proton inhibition of human rho(1)-R was apparently competitive, as observed on rat-rho(1) at acidic pH(o). Titration of the human rho(1)-R gave a single H(+) binding site with a pKa of 6.3, similar to the value for the low pKa on rat rho(1)-R. The pKa value of human rho(1)-R was not dependent on the GABA concentration. A chimeric receptor, consisting of the N-terminal part of the rat rho(1)-R and C-terminal part of the human rho(1)-R, displayed pH(o) sensitivity similar to that observed for rat rho(1)-R. This indicates that the high pKa of rat rho(1)-R is attributable to the 11 amino acid differences between the rat and human rho(1)-R extracellular domains.