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PubMed2006

Cardiac output and muscle blood flow during rest-associated apneas of elephant seals.

In order to evaluate hemodynamics and blood flow during rest-associated apnea in young elephant seals (Mirounga angustirostris), cardiac outputs (CO, thermodilution), heart rates (HR), and muscle blood flow (MBF, laser Doppler flowmetry) were measured. Mean apneic COs and HRs of three seals were 46% and 39% less than eupneic values, respectively (2.1+/-0.3 vs. 4.0+/-0.1 mL kg(-1) s(-1), and 54+/-6 vs. 89+/-14 beats min(-1)). The mean apneic stroke volume (SV) was not significantly different from the eupneic value (2.3+/-0.2 vs. 2.7+/-0.5 mL kg(-1)). Mean apneic MBF of three seals was 51% of the eupneic value. The decline in MBF during apnea was gradual, and variable in both rate and magnitude. In contrast to values previously documented in seals during forced submersions (FS), CO and SV during rest-associated apneas were maintained at levels characteristic of previously published values in similarly-sized terrestrial mammals at rest. Apneic COs of such magnitude and incomplete muscle ischemia during the apnea suggest that (1) most organs are not ischemic during rest-associated apneas, (2) the blood O(2) depletion rate is greater during rest-associated apneas than during FS, and (3) the blood O(2) store is not completely isolated from muscle during rest-associated apneas.

Animals↗
PubMed2006

Respiratory water loss during rest and flight in European Starlings (Sturnus vulgaris).

Respiratory water loss in Starlings (Sturnus vulgaris) at rest and during flight at ambient temperatures (T(amb)) between 6 and 25 degrees C was calculated from respiratory airflow and exhaled air temperature. At rest, breathing frequency f (1.4+/-0.3 Hz) and tidal volume Vt (1.9+/-0.4 ml) were independent of T(amb), but negatively correlated with each other. Mean ventilation at rest was 156+/-28 ml min(-1) at all T(amb). Exhaled air temperature (T(exh)) at rest increased with T(amb) (T(exh) = 0.92.T(amb)+12.45). Respiratory water loss at rest averaged 0.18+/-0.09 ml h(-1) irrespective of T(amb). In flying Starlings f was 4.0+/-0.4 Hz and independent of T(amb). Vt during flight averaged 3.6+/-0.4 ml and increased with T(amb) (Vt = 0.06.T(amb)+2.83) as, correspondingly, did ventilation. T(exh) during flight increased with T(amb) (T(exh) = 0.85.T(amb)+17.29). Respiratory water loss during flight (average REWL(f) = 0.74+/-0.22 ml h(-1)) was significantly higher than at rest and increased with T(amb). Our measurements suggest that respiratory evaporation accounts for most water loss in flying Starlings and increases more than cutaneous evaporation with rising ambient temperature.

Animals↗
PubMed2006

Resting state oscillatory brain dynamics in Parkinson's disease: an MEG study.

OBJECTIVE: The pathophysiological mechanisms of cognitive dysfunction and dementia in Parkinson's disease (PD) are still poorly understood. Altered resting state oscillatory brain activity may reflect underlying neuropathological changes. The present study using magneto encephalography (MEG) was set up to study differences in the pattern of resting state oscillatory brain activity in groups of demented and non-demented PD patients and healthy, elderly controls. METHODS: The pattern of MEG background oscillatory activity was studied in 13 demented PD patients, 13 non-demented PD patients and 13 healthy controls. Whole head MEG recordings were obtained in the morning in an eyes closed and an eyes open, resting state condition. Relative spectral power was calculated using Fast Fourier Transformation in delta, theta, alpha, beta and gamma frequency bands. RESULTS: In the non-demented PD patients, relative theta power was diffusely increased and beta power concomitantly decreased relative to controls. gamma Power was decreased in central and parietal channels. In the demented PD patients, a diffuse increase in relative delta and to lesser extent theta power and a decrease in relative alpha, beta and to lesser extent gamma power were found in comparison to the non-demented PD group. In addition, reactivity to eye opening was much reduced in the demented PD group. CONCLUSIONS: Parkinson's disease is characterized by a slowing of resting state brain activity involving theta, beta and gamma frequency bands. Dementia in PD is associated with a further slowing of resting state brain activity, additionally involving delta and alpha bands, as well as a reduction in reactivity to eye-opening. SIGNIFICANCE: The differential patterns of slowing of resting state brain activity in demented and non-demented PD patients suggests that, in conjunction with a progression of the pathological changes already present in non-demented patients, additional mechanisms are involved in the development of dementia in PD.

Aged↗
PubMed2006

Differences in left ventricular ejection fraction and volumes measured at rest and poststress by gated sestamibi SPECT.

BACKGROUND: Some studies suggested that the poststress left ventricle ejection fraction (LV EF) is lower than rest LV EF in patients with stress-induced ischemia. METHODS AND RESULTS: By using a 2-day protocol and 30 mCi Tc-99m sestamibi, LV EF, end-systolic volume (ESV), and end-diastolic volume (EDV) were measured with gated SPECT. Of 99 eligible patients, 91 had technically adequate studies. Poststress LV EF minus rest LV EF was defined as DeltaLV EF. DeltaEDV and DeltaESV were similarly defined. Rest and poststress LV EF (r = 0.89), EDV (r = 0.78), and ESV (r = 0.93) were highly correlated (P <.001). Rest LV EF, EDV, and ESV were not significantly different between patients with and without stress-induced ischemia. DeltaLV EF was significantly lower in patients with stress-induced ischemia (-3.5% +/- 4.5% vs -1.1% +/- 4.7%, P = .02). Mean LV EF poststress in ischemic patients was 55.0% +/- 10.5% vs 61.2% +/- 10.0% in nonischemic patients (P = .008). However, only 1 patient (3%) with ischemia had DeltaLV EF that exceeded the 95% confidence limit of DeltaLV EF for normal patients. Ischemia was significantly associated with increased DeltaEDV and DeltaESV (P < .01). CONCLUSIONS: Stress-induced ischemia is associated with poststress reduction in LV EF and increased poststress EDV and ESV. However, the effect of ischemia on the difference between poststress and rest EF measurements is modest and rarely exceeds the confidence limits in normal patients undergoing 2-day protocols. In most patients, poststress LV EF is an accurate reflection of rest LV EF.

Aged↗
PubMed2003

Validation of several established equations for resting metabolic rate in obese and nonobese people.

OBJECTIVE: To evaluate several equations for predicting resting metabolic rate against measured values in obese and nonobese people. DESIGN: Resting metabolic rate was measured with indirect calorimetry. Four calculation standards using various combinations of weight, height, and age were used to predict resting metabolic rate: a) Harris-Benedict equation, b) Harris-Benedict equation using adjusted body weight in obese individuals, c) Owen, and d) Mifflin. Main outcome was percentage of subjects whose calculated metabolic rate was outside a +/-10% limit from measured values. Subjects/Setting 130 nonhospitalized adult volunteers grouped by degree of obesity (range of body mass index, 18.8 to 96.8). Statistical Analysis Performed Analysis of proportions was used to determine differences in the percentage of subjects estimated accurately by each equation; alpha was set at 0.05. RESULTS: Calculated resting metabolic rate was more than 10% different from measured in 22% of subjects using the Mifflin equation, 33% using the Harris-Benedict equation (P=.05 vs Mifflin), and 35% using the Owen equation (P<.05 vs Mifflin). The error rate using Harris-Benedict with adjusted weight in obesity was 74% (vs 36% in obese subjects using actual weight in the standard Harris-Benedict equation). APPLICATIONS/CONCLUSION: Of the calculation standards tested, the Mifflin standard provided an accurate estimate of actual resting metabolic rate in the largest percentage of nonobese and obese individuals and therefore deserves consideration as the standard for calculating resting metabolic rate in obese and nonobese adults. Use of adjusted body weight in the Harris-Benedict equation led to less overestimation by that equation in obese people at the expense of increased incidence of underestimation.

Adolescent↗
PubMed1983

Rest and exercise ventricular function in adults with congenital ventricular septal defects.

Rest and exercise right and left ventricular function were compared using equilibrium gated radionuclide angiography in 19 normal sedentary control subjects (mean age 28 years, range 22 to 34) and 34 patients with hemodynamically documented congenital ventricular septal defect (VSD) (mean age 27 years, range 20 to 40). The 34 patients with VSD were divided into 3 groups: those in Group 1 (17 patients) had pulmonary to systemic blood flow ratios of less than 2 to 1; those in Group 2 (12 patients) had prior surgical closure of VSD (mean interval from surgery 17 years, range 9 to 22), and those in Group 3 (5 patients) had Eisenmenger's complex. Gated radionuclide angiography was performed at rest and during each level of graded supine bicycle exercise to fatigue. Heart rate, blood pressure, maximal work load achieved, and right and left ventricular ejection fractions were assessed. The control subjects demonstrated an increase in both the left and right ventricular ejection fractions with exercise (0.70 +/- 0.07 to 0.79 +/- 0.05 and 0.46 +/- 0.06 to 0.57 +/- 0.04; p less than 0.001 for left and right ventricles, respectively). All study groups failed to demonstrate an increase in ejection fraction in either ventricle with exercise. Furthermore, resting left ventricular ejection fraction in Groups 2 and 3 was lower than that in the control subjects (0.59 +/- 0.09 and 0.54 +/- 0.06 versus 0.70 +/- 0.07; p less than 0.001) and resting right ventricular ejection fraction was lower in Group 3 versus control subjects (0.30 +/- 0.07 versus 0.46 +/- 0.06; p less than 0.001). Thus (1) left and right ventricular function on exercise were abnormal in patients with residual VSD as compared with control subjects; (2) rest and exercise left ventricular ejection fractions remained abnormal despite surgical closure of VSD in the remote past; (3) resting left and right ventricular function was abnormal in patients with Eisenmenger's complex; (4) lifelong volume overload may be detrimental to myocardial function.

Adult↗
PubMed1997

Shoulder-arm muscle load and performance during control operation in forestry machines. Effects of changing to a new arm rest, lever and boom control system.

Three work station design studies in forestry machines were carried out with regard to shoulder/arm muscle load. (1) In an arm rest study, a movable (in the sagittal plane) arm rest was compared with a fixed one; (2) in a lever study, a mini lever with a small deflection was compared with an ordinary hand lever; (3) in a boom control study, a computer controlled boom system was compared with an ordinary boom system. In the arm rest study eight male subjects carried out lever operations in the laboratory. In the lever and boom studies, 15 male forestry students operated forwarders. Muscle load, cycle time, skill, perceived exertion, heart rate and preferred set up were recorded. The muscle loads on the upper trapezius, infraspinatus, extensor carpi ulnaris and flexor carpi radialis were recorded by electromyography. With mini lever and movable arm rest the upper trapezius load was reduced with preserved or decreased cycle time, although the grand mean of the 'static' load level was only about 2% of maximal voluntary contraction (MVC) and the effects of the new designs were small (about 0.7% MVC). The subjects preferred the lever/arm rest also giving the lowest muscle load. No differences between levers or arm rests were found in skill, perceived exertion or heart rate. It was not possible to draw any definitive conclusions regarding effects of the boom control system, due to technical problems. According to the literature, the duration of lever operation has increased considerably in forestry during recent years as part of a rationalization process. Partly due to this, it is suggested that the investigated work station improvements may not be sufficient to eliminate the risk for shoulder-neck disorders.

Arm↗
PubMed1989

Uptake and subcellular distribution of cadmium in resting and mitogen-activated lymphocytes and its relationship to a metallothionein-like protein.

The effects of cadmium on the immune system have been extensively studied, although relatively little is known about the nature of the interaction between cadmium and lymphocytes. We describe studies that examine the uptake and subcellular distribution of cadmium in resting and mitogen-activated mouse splenic lymphocytes exposed to cadmium in vitro. Mitogen activation was associated with an increased uptake and altered subcellular distribution of cadmium, compared to resting (nonmitogen-activated) lymphocytes. In both resting and mitogen-activated lymphocytes the total uptake of cadmium was concentration-dependent. However, compared to resting lymphocytes, in mitogen-activated lymphocytes, cadmium tended to distribute out of the nuclear and into the cytoplasmic fraction. The Sephadex G-75 exclusion chromatography profile revealed the presence of a cadmium-binding protein eluting identically to metallothionein in mitogen-activated, but not in resting, lymphocytes. The presence of this protein in mitogen-activated lymphocytes is consistent with the differences in subcellular distribution of cadmium reported. Further, the difference between resting and mitogen-activated lymphocytes in the production of this protein, and the known genetic differences in the metallothionein inducibility, may explain some of the reported variability in the effects of cadmium on the immune system.

Animals↗
PubMed1987

Characterization of isolated ventricular myocytes: two levels of resting potential.

Standard microelectrode and whole cell patch clamp techniques were used to characterize the resting properties of ventricular myocytes obtained by enzymatic dispersion from rabbit hearts. In 37 cells studied under current clamp using intracellular microelectrodes, three distinct group of cells can be recognized. The first group (23 cells) is constituted by permanently depolarized cells (RP = -24 +/- 5 mV; Rm = 8.1 +/- 3.4 K omega cm2; Cm = 2.4 +/- 1.2 microF/cm2). A second group (13 cells) is constituted by cells able to be in two distinct states: D state (RP = -28 +/- 11 mV; Rm = 15.2 +/- 9.1 k omega cm2; Cm = 3.8 +/- 0.8 microF/cm2) and H state (RP = -74 +/- 8 mV; Rm = 3.2 +/- 2.3 K omega cm2 and Cm = 2.9 +/- 2.3 microF/cm2). Some of these cells were able to switch between the two states. The third group is represented by one cell and had only one resting potential in the H state range. Resting potential of permanently depolarized cells and cells in D state did not depend on extracellular potassium concentration. In H state however, it varied with extracellular potassium for concentrations above 2.5 mM as expected for a potassium electrode; for lower concentrations a strong deviation was observed. Accordingly, the steady state current voltage plot obtained under whole cell voltage clamp conditions showed either one zero current potential with positive slope conductance at the D state resting range; two zero current voltages corresponding to D and H state resting levels or only one zero current potential at H state resting level.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

Laterality of tail resting posture in three species of New World primates.

A variety of mammalian species including prosimian and simian primates wrap their tails around their bodies as a means of thermoregulation and for reasons of comfort during resting or sleep. Adopting such a resting posture requires an animal to move its tail either to the right or to the left of the midline of its body, and thus to perform a lateralized behavior. The purpose of this study was to assess the occurrence of lateral biases in tail resting posture in three species of New World primates. Twenty squirrel monkeys, spider monkeys, and howler monkeys, respectively, were observed and data on tail resting posture were collected and analyzed. The results demonstrate (1) that individual squirrel monkeys and spider monkeys exhibit highly significant lateral biases in tail resting posture; (2) a lack of a lateral bias at the group level; (3) that howler monkeys fail to show side preferences in tail wrapping; (4) a lack of sex differences in this behavior in all three species; and (5) a lack of significant correlations between preferred side of tail resting posture and preferred side of hand use in simple reaching tasks which had been assessed with a subset of animals in previous studies. Thus, the present study provides evidence for a behavioral asymmetry which is well-known to occur in rats but has not been described so far in nonhuman primates, and which might offer an additional approach to the investigation of the mechanisms underlying functional cerebral asymmetries.

Alouatta↗
PubMed2001

Effect of lithium and sodium valproate ions on resting membrane potentials in neurons: an hypothesis.

In an attempt to understand the therapeutic effects of lithium and sodium valproate in stabilizing the moods in manic depressive illness, the well-known Goldman-Hodgkin-Katz (G-H-K) equation is modified to include a fourth ion, such as a lithium ion or a sodium ion. The modified G-H-K equation is used to calculate the resting membrane potential in neurons. These calculations show that the resting membrane potential is depolarized depending upon the relative concentration of the lithium ion and upon its relative permeability. These calculations suggest that the resting membrane potential may be hyperpolarized in bipolar patients before treatment, and that the lithium ion perhaps depolarizes the resting membrane potential back to the normal level. They further support the prevailing hypothesis that manic-depressive illness may be caused by the hyperpolarization of the resting membrane potential, which, in turn, may be caused by the changes in ionic conductance (permeability) of the membranes. Sodium ions in sodium valproate do not significantly affect the resting membrane potential since they do not significantly change in the serum.

Bipolar Disorder↗
PubMed1997

Chinrest pressure in violin playing: type of music, chin rest, and shoulder pad as possible mediators.

INTRODUCTION:: This study was conducted to determine if there are differences in pressure on a violin chin rest during performance due to changes in shoulder pads, chin rests, or pieces of music performed. It was also hypothesized that these differences would correlate with anthropometric measurements made of the subjects' necks and shoulders. METHODS::: A Novel EMED pad was used over the chin rest, containing 120 sensors, each one centimetre squared. The sampling rate was 50 Hz. A total of ten subjects, all professional violinists, performed excerpts from a Bruch violin concerto and a Handel sonata. Anthropometric measurements were made of the subjects' necks and shoulders. Each subject began by using his own violin with his usual shoulder pad and chin rest set-up, and then with the author's violin. Two different shoulder pads and three different chin rests were placed on the violin, in all possible combinations, for both pieces of music. This resulted in a total of fourteen conditions given in randomized order for each subject. Subjects were asked to give verbal feedback regarding the comfort and ease of playing of each shoulder pad and chin rest. Data was collected for three trials of each condition, and a mean for the three trials was obtained for each dependent variable. The five dependent variables were: peak pressure, maximum force, pressure/time integral and force/time integral, and total contact area. Intraclass coefficients of reliability were calculated for the dependent variables. Pearson's correlation coefficients were computed to determine if there were significant relationships between the five dependent variables and violin height, shoulder width, and neck length. RESULTS:: Pressure/time integral achieved the highest reliability with a coefficient of 0.9310, followed by peak pressure at 0.9152, force/time integral at 0.8817, maximum force at 0.8685, and total area at 0.8571. Multivariate analysis of variance detected significant differences in levels of pressure and force for the different conditions. Subsequent one-way ANOVAS andt -tests determined significantly less pressure on the Wolf chinrest as compared to the other chinrests. There were also reliable differences in pressure between the two pieces of music, with the Handel sonata excerpt showing significantly less pressure. There were no differences detected between the two shoulder pads. Significant relationships between neck length and shoulder width, and peak pressure, pressure/time integral, maximum force, force/time integral, and total contact area were found. A discussion of these results, and conclusions and implications for further study, are currently in progress.

Journal Article↗
PubMed1999

The effects of long-term bed rest on H-reflex and motor evoked potential in the human soleus muscle during standing.

H-reflex and motor evoked potential (MEP) induced by transcranial magnetic stimulation (TMS) in soleus muscle of five normal subjects were investigated before and after 20 days 6 degree head-down bed rest (BR). Soleus H-reflex during standing following bed rest decreased in all five subjects. The size of the maximum H-reflex (Hmax), expressed as a percentage of the maximum M-response (Mmax), decreased from 63.3+/-23.3% before BR to 26.7+/-12.5% after BR. However, there were no significant differences between MEPs before and after bed rest. Moreover, MEP/Hmax after bed rest was larger than before bed rest in all subjects. These results indicate a strong inhibition of H-reflex and no adaptation of MEP in soleus muscle during standing following bed rest.

Electromyography↗
PubMed2001

Chemical hypoxia in hippocampal pyramidal cells affects membrane potential differentially depending on resting potential.

The aim of the present study was to analyze the effect of chemical hypoxia (cyanide) on the membrane potential of hippocampal CA1 neurons and to elucidate the reason for previously found differences in the reaction to hypoxia in these cells. Recordings were performed in brain slices from 8-19-day-old rats with whole-cell patch clamp on cells identified with near-infrared video microscopy. Cyanide (0.1-2.0 mM) caused different responses depending on the resting potential of the cells: hyperpolarization (or an initial depolarization followed by hyperpolarization) was generally seen in cells with less negative resting potential (-56+/-6.1 mV), and depolarization in cells with more negative resting potential (-62+/-3.4 mV). After 10 min in cyanide the membrane potential in all cells had reached approximately the same level (-62+/-5.8 mV), the direction and size of the voltage response having an inverse linear relation to the resting potential (k=-0.98, r=0.71). The direction of the cyanide response was not reversed by current injection (depolarization by 12 mV) in cells with more negative resting potential (-60+/-2.8 mV). Wash out of cyanide caused hyperpolarization in 70% of the cells. Presence of ouabain (2 microM) resulted in pronounced depolarization during cyanide perfusion, and potentiated the hyperpolarization during wash out indicating that this part of the effect is not dependent on a reactivation of the Na/K pump. In conclusion, chemical hypoxia with cyanide changes the membrane potential in CA1 cells in size and direction depending on the original resting potential of the cells. The present findings suggested that cyanide activated not only K+ channels but in addition increased a Na+ current which has a more positive equilibrium potential.

Animals↗
PubMed2002

REST mRNA expression in normal and regenerating avian auditory epithelium.

Hair cells (HCs) and supporting cells (SCs) in the auditory epithelium initially arise from a sheet of undifferentiated cells. Although much has been learned about the initial steps leading to the fate determination of HCs and SCs, respectively, little is known about what molecular events 'finalize' cell fate determination. We investigated the role of repressor element-1 (RE-1) silencing transcription factor (REST), whose inactivation is known to be a requirement for a cell to assume a neuronal identity. Here we show by in situ hybridization (ISH) that SCs express REST messenger RNA (mRNA) but sensory HCs lack detectable expression. Using a more sensitive reverse transcription-polymerase chain reaction assay, however, we detected the presence of a neuron-specific splice variant in the epithelium, suggesting that HCs express REST mRNA at levels too low to be detectable by ISH. In regenerating auditory epithelium, we found that REST mRNA was expressed and upregulated in all remaining cells in the damaged region of the epithelium, consistent with its expression pattern during development prior to neurogenesis. Surprisingly, REST mRNA was also upregulated in SCs in the apical, undamaged region of the epithelium, and readily detectable by ISH in the HCs in this region. This finding suggests that the grossly undamaged region of the epithelium is in fact biochemically altered towards a 'less developed' state. Our results indicate that REST inactivation is an important step in finalizing HC fate in the chick inner ear.

Animals↗
PubMed1998

A 10-year follow-up of patients presenting with ischaemic rest pain of the lower limbs.

OBJECTIVES: To determine the 10-year outcome of patients presenting with rest pain. METHODS: One hundred and three consecutive patients presenting with ischaemic rest pain in 1987 were followed up after 10 years. Hospital notes, death certificates and telephone interviews with patients were used to determine outcome. RESULTS: Follow-up data is available for 97 (94%) patients. Thirteen patients are alive (13.7%) after 10 years, 12 presented with rest pain alone and one had ulceration. Three of these had amputation. The commonest cause of death was myocardial infarction (n = 21, 25%). In those who had died, the median age of onset of symptoms was 72 years (49-93) for rest pain, 74 years (56-87) for ulceration and 71.5 years (45-85) for gangrene. Their survival after admission was a mean of 39 months with rest pain, 33 months with ulceration and 42 months with gangrene. The overall 5-year survival was 31% and the 10-year survival 13%. CONCLUSION: Patients presenting with ischaemic rest pain have a poor prognosis. The presence or absence of ulceration or gangrene does not influence the outcome. Most patients die from smoking-related diseases.

Adult↗
PubMed2000

Absolute value of the difference of Tl-201 uptake between redistribution and rest is a specific marker of myocardial viability.

Although Tl-201 rest redistribution SPECT is widely used to assess myocardial viability, there is no agreement on the best prognostic marker of left ventricle contraction improvement after revascularization. More recent data suggest that not only rest or redistribution uptake but also reverse redistribution patterns may serve to indicate the viability of myocardium. The aim of this study was to define criteria (which include reversibility and reverse redistribution) for viability testing and prediction of functional outcome in Tl-201 rest redistribution SPECT. Twenty-five patients with left ventricle dyssynergy were studied before and after revascularization with Tl-201 SPECT and echocardiography. Perfusion and contractility was assessed in a 16-segment model of the left ventricle. Out of 400 left ventricular segments, contraction disturbances of various degree of intensity (hypokinesis, akinesis and dyskinesis) were found by echocardiography in 107 segments. Revascularization was performed in 97 segments. In 57% of the segments, improvement of contraction was observed after PTCA or CABG. Perfusion was analysed in the segments between segments with and without contraction improvement. In discriminant analysis, only the modulus of difference between rest and redistribution study > or = 10% was the common parameter for hypo-, a- and dyskinetic segments to predict the functional recovery of left ventricle (LV) with the specificity of 93% and sensitivity of 78%. The modulus of segmental quantitative difference between redistribution and rest image is a new parameter adding specificity to Tl-201 rest redistribution SPECT in prediction of recovery of left ventricle function.

Adult↗
PubMed1999

The relation between the action potential duration, the increase in resting tension, and ATP content during metabolic inhibition in guinea pig ventricular muscles.

To investigate whether the action potential duration (APD) or resting tension was dependent on global ATP content, and whether they were preferentially dependent on glycolytic ATP, APD and resting tension were measured under various metabolic inhibition with corresponding measurement of ATP content in guinea pig ventricular muscles. Oxidative phosphorylation was inhibited by either hypoxic perfusion, the perfusion of sodium cyanide, or 2,4-dinitrophenol. Glycolysis was blocked by the perfusion of iodoacetic acid, and hypoxia with variable glycolytic activities was achieved by hypoxic perfusion in the presence of glucose (5, 10, and 50 mM). APD began to decrease when ATP content decreased to less than 3 mM/kg w.w. from the control level of 4.35 mM/kg w.w. APD shortened significantly and resting tension increased steeply, when ATP content decreased below 1 mM/kg w.w. The dependence of APD and the increase in resting tension on ATP content was not affected by the mode of metabolic block, that is, the inhibition of glycolysis and/or oxidative phosphorylation. Though other factors can affect APD and resting tension, we found no evidence of functional ATP compartmentation, with respect to APD and the increase in resting tension during metabolic inhibition.

2,4-Dinitrophenol↗