Effects of reduced PO2 on rapid-drive-induced hyperpolarization of diastolic transmembrane potential in feline cardiac Purkinje strands

1982 ◽  
Vol 60 (12) ◽  
pp. 1519-1525
Author(s):  
David G. Benditt ◽  
Melvin M. Scheinman ◽  
Thomas R. Snow ◽  
Harold C. Strauss
Keyword(s):  
Steady State ◽  
Time Course ◽  
Transmembrane Potential ◽  
Control Period ◽  
Frequency Dependent ◽  
Control Value ◽  
Final Steady State ◽  
Dependent Potential ◽  
The Difference ◽  
Function Time

Using standard microelectrode techniques, we evaluated effects of diminished oxygen tension on the magnitude and time course of frequency dependent changes in maximum diastolic transmembrane potential (MDP) and on alteration of action potential duration (APD) in feline Purkinje fibers. MDP was recorded continuously during a control period (cycle length (CL) = 1000 ms), during a 5-min period of rapid drive (CL = 400 ms) and following return to pacing CL = 1000 ms. Rapid drive resulted in hyperpolarization of MDP from control value; and after return to pacing CL = 1000 ms, MDP gradually depolarized, eventually attaining a steady state value within ± 0.5 mV of the control value. The difference between hyperpolarized MDP value and final steady-state value was designated VH, and the decline of MDP towards steady-state value approximated an exponential function (time constant = τVH). Exposure to reduced [Formula: see text] (75 ± 2.1 mmHg vs. control 473 ± 39.1 mmHg) (1 mmHg = 133.322 Pa) resulted in reduction in the magnitude of VH (6.2 ± 3.43 mV vs. 7.8 ± 2.73 mV, mean ± SD, p < 0.005) and shortening of APD within 0–24 min, while measurable prolongation of τVH (75 ± 18.5 vs. 54 ± 9.0 s, p < 0.005) began at 25–49 min following onset of reduced [Formula: see text]. These observations suggest that rate-related changes of MDP in cardiac tisues are oxygen dependent, and they support previously reported analagous observations in nerve which suggested that frequency dependent potential changes may in part reflect alterations of electrogenic Na-K pump activity.

Effects of myocardial hypertrophy on transient outward current

1994 ◽  
Vol 266 (5) ◽  
pp. H1738-H1745 ◽  
Author(s):  
Q. Li ◽  
E. C. Keung
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Action Potential Duration ◽  
Time Course ◽  
Myocardial Hypertrophy ◽  
Pressure Overload ◽  
Reversal Potential ◽  
Outward Current ◽  
Transient Outward Current ◽  
The Difference

In the one-clip, two-kidney model of hypertensive rat, a gradual chronic pressure overload is imposed on the heart. Myocardial hypertrophy resulting from such pressure overload is associated with an increased but slower inactivating L-type calcium current and prolongation of action potential duration. Voltage clamp experiments in a variety of excitable tissues indicate that a 4-aminopyridine-sensitive transient outward current (Ito) plays an important role in regulating the action potential duration. Accordingly, we studied Ito in single adult cardiac myocytes enzymatically isolated from hypertrophied left ventricles of the renovascular hypertensive (HBP) rat hearts using the whole cell patch-clamp method. The current densities (normalized to cell capacitative surface area) measured at the early transient peak Ito, at the steady state, and as the difference between the transient peak and the steady state were larger in HBP cells (n = 23) than in control (Ctrl) cells (n = 20) (P < 0.05). There was no difference in the Ito reversal potential between Ctrl (-60.9 +/- 1.9 mV, mean +/- SE; n = 16) and HBP (-63.7 +/- 2.6 mV; n = 19) cells. The observed increase in Ito amplitude was not due to an increase in the number of channels available for activation or in the fraction of channels activated because there were no statistical differences in the membrane potential at which one-half of the Ito channels are activated (V0.5) for the steady-state activation and inactivation curves between Ctrl and HBP cells. The time course of inactivation of Ito was described by a double-exponential function.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient responses to CO2 breathing of human subjects awake and asleep

1963 ◽  
Vol 18 (2) ◽  
pp. 289-294 ◽  
Author(s):  
F. J. D. Fuleihan ◽  
T. Nakada ◽  
J. T. Suero ◽  
E. S. Merrifield ◽  
R. E. Dutton ◽  
...  
Keyword(s):  
Steady State ◽  
Ventilatory Response ◽  
Human Subjects ◽  
Control Period ◽  
Sodium Pentobarbital ◽  
Transient Responses ◽  
Control Value ◽  
Oxygen Breathing ◽  
Significant Difference ◽  
End Tidal

Ventilation and end-tidal Pco2 were studied in six subjects awake and asleep (following the ingestion of 200–300 mg sodium pentobarbital) during oxygen breathing and the administration and withdrawal of 4% CO2 in oxygen. During the control period as well as steady-state CO2 breathing, ventilation was significantly lower in asleep than in awake subjects. There was no significant difference between sleep and wakefulness in end-tidal Pco2 or in the slope of the ventilatory response to 4% CO2. The transient responses of ventilation and end-tidal Pco2 of the group as a whole were similar in sleep and wakefulness. Ventilation changed more slowly than did end-tidal Pco2. End-tidal Pco2 overshot beyond the steady-state CO2 breathing value at the onset of CO2 breathing; and undershot below the control value during recovery. The magnitudes of both the overshoot and undershoot of end-tidal Pco2 were correlated significantly to the slope of the ventilatory response to 4% CO2, in the whole group awake and asleep. Submitted on October 4, 1962

Luminal and peritubular ionic substitutions and intracellular potential of the rabbit proximal convoluted tubule

1984 ◽  
Vol 247 (2) ◽  
pp. F352-F364 ◽  
Author(s):  
J. Cardinal ◽  
J. Y. Lapointe ◽  
R. Laprade
Keyword(s):  
Time Course ◽  
Control Period ◽  
Complete Recovery ◽  
Control Solution ◽  
Similar Time ◽  
Control Value ◽  
Transient Nature ◽  
The Mean ◽  
Convoluted Tubules

Transepithelial (psi T) and basolateral (psi BL) potential difference was measured in rabbit proximal convoluted tubules perfused in vitro. In control solution without protein, the mean psi BL was -54 +/- 2.2 mV (n = 57). Luminal substitution of K by Na had no effect. Complete luminal substitution of glucose and alanine, 110 mM substitution of Na or NaCl produced transient hyperpolarizations of psi BL of 14, 10, and 13 mV, respectively, with a return close to the control value within 4-8 min in all cases. Returning to control solution produced similar time-course transient depolarizations of psi BL of 17, 11, and 16 mV, respectively, again with a return to the control value in 4-10 min. Omission of glucose and alanine in the perfusate produced a decrease in cell volume of 14% that was maximal in 4 min with a complete recovery in the post-control period. A 110 mM luminal or peritubular substitution of Cl by cyclamate produced no significant effect on psi BL after taking into account the large psi T generated by the diffusion of Cl across the paracellular pathway. On the other hand, complete peritubular substitution of K by Na and 110 mM substitution of Na or NaCl produced sustained but reversible depolarizations of psi BL of 37.5, 10.2, and 20.4 mV, respectively. The transient nature of the hyperpolarization following luminal substitution of glucose, alanine, or Na can be interpreted in terms of changes in the intracellular sodium activity that would affect the Na-K-ATPase pump. Similarly, the sustained depolarization seen after a peritubular substitution of K and Na would also be compatible with a decrease in the basolateral ionic pump activity.

Erythropoietin under real and simulated microgravity conditions in humans

1996 ◽  
Vol 81 (2) ◽  
pp. 761-773 ◽  
Author(s):  
H. C. Gunga ◽  
K. Kirsch ◽  
F. Baartz ◽  
A. Maillet ◽  
C. Gharib ◽  
...  
Keyword(s):  
Time Course ◽  
Venous Pressure ◽  
Recovery Period ◽  
Control Period ◽  
Control Level ◽  
Bed Rest ◽  
Control Value ◽  
Real Microgravity ◽  
Microgravity Conditions

The aim of this study was to analyze the time course of erythropoietin (EPO) during Earth-bound microgravity simulations such as bed rest, isolation and confinement (IC), head-down tilt (HDT; -6 degrees), and immersion to evaluate which factors could contribute to alterations in EPO under real microgravity conditions during and after short- (< 10 days) and long-term (> 6 mo) spaceflights. During bed rest (24h), no significant changes in EPO could be observed. Subjects confined in a diving chamber facility for 60 days showed a decrease in EPO. In the recovery period a slight increase was observed, but EPO concentrations did not reach the pre-IC control level. In the control period before HDT, subjects showed normal resting values for EPO, but on day 2 of HDT the EPO concentrations were decreased (P < 0.01). Later the EPO levels remained below the control value and were increased after HDT (P < 0.05). After immersion (24 h) increased EPO concentrations could be determined (P < 0.05). During a short-term spaceflight the astronauts showed in-flight (day 4) decreased and unchanged EPO concentrations. During a long-term spaceflight, 24 h after recovery, the cosmonaut showed slightly elevated EPO concentration, which increased markedly during the following days. It is concluded that 1) HDT (-6 degrees) causes a rapid decrease in EPO in humans, 2) IC per se leads to diminished EPO concentrations, 3) EPO regulation in humans during short- and long-term spaceflights might be different, 4) changes in central blood volume, i.e., central venous pressure, seem to be involved in the modulation of EPO production and release under simulated and real microgravity conditions, and 5) the HDT (-6 degrees) Earth-bound simulation reflects mostly the changes in EPO production and release observed under real microgravity conditions in humans.

Destruction of Actin Filaments by Osmium Tetroxide

1977 ◽  
Vol 35 ◽  
pp. 466-467
Author(s):  
P. Maupin-Szamier ◽  
T. D. Pollard
Keyword(s):  
Actin Filaments ◽  
Time Course ◽  
Osmium Tetroxide ◽  
Rabbit Muscle ◽  
Muscle Actin ◽  
Sodium Phosphate Buffer ◽  
Transmission Electron ◽  
The Difference ◽  
Rates Of Decay ◽  
Short Time

We have studied the destruction of rabbit muscle actin filaments by osmium tetroxide (OSO4) to develop methods which will preserve the structure of actin filaments during preparation for transmission electron microscopy.Negatively stained F-actin, which appears as smooth, gently curved filaments in control samples (Fig. 1a), acquire an angular, distorted profile and break into progressively shorter pieces after exposure to OSO4 (Fig. 1b,c). We followed the time course of the reaction with viscometry since it is a simple, quantitative method to assess filament integrity. The difference in rates of decay in viscosity of polymerized actin solutions after the addition of four concentrations of OSO4 is illustrated in Fig. 2. Viscometry indicated that the rate of actin filament destruction is also dependent upon temperature, buffer type, buffer concentration, and pH, and requires the continued presence of OSO4. The conditions most favorable to filament preservation are fixation in a low concentration of OSO4 for a short time at 0°C in 100mM sodium phosphate buffer, pH 6.0.

scholarly journals Effects of Genotypes and Treatment on Oxygenscan Parameters in Sickle Cell Disease

Cells ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 811
Author(s):  
Camille Boisson ◽  
Minke A. E. Rab ◽  
Elie Nader ◽  
Céline Renoux ◽  
Celeste Kanne ◽  
...  
Keyword(s):  
Steady State ◽  
Sickle Cell Disease ◽  
Blood Cell ◽  
Sickle Cell ◽  
Red Blood Cell ◽  
Cell Disease ◽  
Oxygen Gradient ◽  
Acute Complication ◽  
Adults And Children ◽  
The Difference

(1) Background: The aim of the present study was to compare oxygen gradient ektacytometry parameters between sickle cell patients of different genotypes (SS, SC, and S/β+) or under different treatments (hydroxyurea or chronic red blood cell exchange). (2) Methods: Oxygen gradient ektacytometry was performed in 167 adults and children at steady state. In addition, five SS patients had oxygenscan measurements at steady state and during an acute complication requiring hospitalization. (3) Results: Red blood cell (RBC) deformability upon deoxygenation (EImin) and in normoxia (EImax) was increased, and the susceptibility of RBC to sickle upon deoxygenation was decreased in SC patients when compared to untreated SS patients older than 5 years old. SS patients under chronic red blood cell exchange had higher EImin and EImax and lower susceptibility of RBC to sickle upon deoxygenation compared to untreated SS patients, SS patients younger than 5 years old, and hydroxyurea-treated SS and SC patients. The susceptibility of RBC to sickle upon deoxygenation was increased in the five SS patients during acute complication compared to steady state, although the difference between steady state and acute complication was variable from one patient to another. (4) Conclusions: The present study demonstrates that oxygen gradient ektacytometry parameters are affected by sickle cell disease (SCD) genotype and treatment.

Inhibition of cardiac vagal component of baroreflex by group III and IV afferents

1991 ◽  
Vol 260 (3) ◽  
pp. H730-H734 ◽  
Author(s):  
P. N. McWilliam ◽  
T. Yang
Keyword(s):  
Peroneal Nerve ◽  
Baroreceptor Reflex ◽  
Interval Prolongation ◽  
Group Iii ◽  
Control Value ◽  
Pressure Elevation ◽  
Group I ◽  
Afferent Fibers ◽  
The Difference ◽  
The Right

The action of electrically evoked activity in somatic afferent fibers on the sensitivity of the baroreceptor reflex was examined in decerebrate cats. The sensitivity of the reflex was expressed as the difference between the maximum prolongation of R-R interval in response to carotid sinus pressure elevation and the mean of 10 R-R intervals immediately before pressure elevation. The control value of R-R interval prolongation was 192 +/- 50 ms. Stimulation (10 Hz) of group I and II fibers of the right peroneal nerve (evoked volleys recorded from the sciatic nerve) had no effect on R-R interval prolongation (171 +/- 45 ms). Recruitment of group III fibers (10 Hz) conducting at 23.6 +/- 0.65 m/s reduced the prolongation of R-R interval to 52 +/- 14 ms. Recruitment of group IV fibers (10 Hz) conducting less than 2.5 m/s further reduced the prolongation of R-R interval to 1.0 +/- 8.0 ms. It is concluded that the inhibition of the cardiac vagal component of the baroreceptor reflex produced by electrical stimulation of the peroneal nerve is mediated by afferent fibers of groups III and IV.

Inward rectification in rat nucleus accumbens neurons

1989 ◽  
Vol 62 (6) ◽  
pp. 1280-1286 ◽  
Author(s):  
N. Uchimura ◽  
E. Cherubini ◽  
R. A. North
Keyword(s):  
Steady State ◽  
Nucleus Accumbens ◽  
Time Course ◽  
Potassium Conductance ◽  
Resting Potential ◽  
Inward Rectification ◽  
Resting Membrane Potential ◽  
Potential Range ◽  
Inward Current ◽  
Rat Nucleus Accumbens

1. Intracellular recordings were made from neurons in slices cut from the rat nucleus accumbens septi. Membrane currents were measured with a single-electrode voltage-clamp amplifier in the potential range -50 to -140 mV. 2. In control conditions (2.5 mM potassium), the resting membrane potential of the neurons was -83.4 +/- 1.1 (SE) mV (n = 157). Steady state membrane conductance was voltage dependent, being 34.8 +/- 1.7 nS (n = 25) at -100 mV and 8.0 +/- 0.7 nS (n = 25) at -60 mV. 3. Barium (1 microM) markedly reduced the inward rectification and caused a small inward current (40.6 +/- 8.7 pA, n = 8) at the resting potential. These effects became larger with higher barium concentrations, and, in 100 microM barium, the current-voltage relation was straight. 4. The block of the inward current by barium (at -130 mV) occurred with an exponential time course; the time constant was approximately 1 s at 1 microM barium and less than 90 ms with 100 microM. Strontium had effects similar to those of barium, but 1000-fold higher concentrations were required. Cesium chloride (2 mM) and rubidium chloride (2 mM) also blocked the inward rectification; their action reached steady state within 50 ms. 5. It is concluded that the nucleus accumbens neurons have a potassium conductance with many features of a typical inward rectifier and that this contributes to the potassium conductance at the resting potential.

On the steady-state solution of the M/G/2 queue

1979 ◽  
Vol 11 (01) ◽  
pp. 240-255 ◽  
Author(s):  
Per Hokstad
Keyword(s):  
Steady State ◽  
General Solution ◽  
Laplace Transform ◽  
Queue Length ◽  
Joint Distribution ◽  
Length Distribution ◽  
Steady State Solution ◽  
Queue Length Distribution ◽  
The Difference ◽  
Number Of Customers

The asymptotic behaviour of the M/G/2 queue is studied. The difference-differential equations for the joint distribution of the number of customers present and of the remaining holding times for services in progress were obtained in Hokstad (1978a) (for M/G/m). In the present paper it is found that the general solution of these equations involves an arbitrary function. In order to decide which of the possible solutions is the answer to the queueing problem one has to consider the singularities of the Laplace transforms involved. When the service time has a rational Laplace transform, a method of obtaining the queue length distribution is outlined. For a couple of examples the explicit form of the generating function of the queue length is obtained.

Sign in / Sign up

Export Citation Format

Share Document