Secondary CO2 diffusion following HCO3- shift across the red blood cell membrane.

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To describe the overall gas exchange rates in red blood cells (RBC), a computer program for solving the diffusion equations for 02, C02, and HC03 -that accompany the chemical reactions of Bohr-and Haldane-effects was developed. Three diffusion equations were solved alternatively and repeatedly in an increment time of 2 ms. After solving the diffusion equations the Poz, 02 saturation (S02), P02, pH, and HCO3 content were corrected by using the Henderson-Hasselbalch equation, where the buffer value was newly derived from the C02 dissociation curve. In computing the Haldane effect, the buffer value was taken to be 44 mmol l(RBC) -1 pH~ -1, so that the change in intracellular dissolved C02 caused by the Soz change was fully compensated by the subsequent C02 diffusion. The oxygenation and deoxygenation rate factors of hemoglobin were assumed to be 2.09(1 • -S)2'02 and 0.3 s -• Torr 1, respectively. The Poz change due to the Bohr-shift was computed from Hill's equation, in which the K value was given by a function of the intracellular pH. When the parameter values thus far measured were used, the computed Bohr-and Haldane-effects coincided well with the experimental data, supporting the validity of the equations. The overall gas exchange profiles calculated in the pulmonary capillary model showed that the C02 equilibration time was significantly longer than the oxygenation time.Key words ; diffusion in red blood cell, Bohr effect, Haldane effect, overall gas exchange rate.Under physiological conditions in the pulmonary and peripheral capillaries, the 02 and C02 diffusions into and out of the red blood cells (RBC) are mutually influenced by the Bohr-and Haldane-effects. To estimate the overall gas exchange rate, the oxygenation and deoxygenation rates as well as the C02 and HC03 -diffusion rates in the RBC must be solved simultaneously. However, because of

Section: Of Parameter Valuesmentioning

confidence: 99%

Numerical solution of partial differential equations describing the simultaneous O2 and CO2 diffusions in the red blood cell.

Mochizuki

Kagawa

1986

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“…02 and C02 at the RBC membrane, which were both equal to 2.5 x 10-6cm•s-1 •Torr-1 [9,10,16,23,24]. Setting k = 6.58 x 10-3cm•s-' •Atm-1 together with the measured rj value into Eq.…”

Section: Evaluation Of the K And S Values For 02 Co And Co2mentioning

confidence: 99%

mentioning

confidence: 91%

“…UCHIDA et al [31] measured the C02 diffusion rate in a thin layer of hemoglobin solution, and found that the inward and outward diffusions were equally retarded at the gas-liquid interface. NIIZEKI et al [23,24] measured the C02 diffusion rate in the RBC under lowered convective conditions and found that the value of tj for C02, being 2.5 x 10-6 cm • s-1 • Torr-1, was identical to that for 02 [9,10,16].Oxygenation and deoxygenation reactions of hemoglobin are very fast [20] and hydration and dehydration reactions of C02 are also highly accelerated by carbonic anhydrase in RBC [23]. Thus, the rates of 02 and C02 reactions with RBC are limited by the transfer rates of these gases and HC03 -ion across the RBC interface as well as by the intracellular diffusion rate.…”

mentioning

confidence: 99%

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Relationship between the transfer rate and the gap in partial pressure of gas molecules at a heterogeneous interface.

Mochizuki¹

1988

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The partial pressure of a gas corresponds to the kinetic energy per unit volume. At equilibrium, the kinetic energy in the gas phase, or the partial pressure of the gas, must be equal to that in the liquid phase. On the other hand, the number of gas molecules dissolved in a unit volume of solution is usually smaller than the number of molecules in the same volume of gas. Consequently, the kinetic energy of a gas molecule in solution must be higher than that in the gas phase. Thus, in order for the gas molecule to cross a heterogeneous interface, it must undergo a rise of fall in kinetic energy. To counter the change in energy transfer rate across the interface, a gap in partial pressure appears essential.We [18] introduced a term, transfer coefficient, to evaluate the relationship between the magnitude of the gap in partial pressure and the transfer rate across the red blood cell (RBC) membrane. The transfer coefficient (ii) was obtained by dividing the diffusion flux by the size of the gap in partial pressure. Thus, the dimensions are similar to those of permeability. However, , is concerned with the discontinuity in partial pressure at heterogeneous interface caused by the difference in kinetic energy, while permeability is related to the diffusibility within a thin layer such as is found in artificial and some biological membranes. UCHIDA et al. [31] measured the C02 diffusion rate in a thin layer of hemoglobin solution, and found that the inward and outward diffusions were equally retarded at the gas-liquid interface. NIIZEKI et al. [23,24] measured the C02 diffusion rate in the RBC under lowered convective conditions and found that the value of tj for C02, being 2.5 x 10-6 cm • s-1 • Torr-1, was identical to that for 02 [9,10,16].Oxygenation and deoxygenation reactions of hemoglobin are very fast [20] and hydration and dehydration reactions of C02 are also highly accelerated by carbonic anhydrase in RBC [23]. Thus, the rates of 02 and C02 reactions with RBC are limited by the transfer rates of these gases and HC03 -ion across the RBC interface as well as by the intracellular diffusion rate. Therefore, estimation of the i values of the RBC and alveolar membranes is a key problem for the kinetic studies in the

“…Thus, we first attempted to obtain the i1(C02) and the HC03-permeability, i2(HC03-), simultaneously from the two experimental data on the C02 diffusion and HC03-shift through the trial-and-error method. NIIZEKI et al (1984) measured the rate of the HC03-shift in a closed RBC suspension and clarified that the intracellular HC03-change caused the P02 change, and subsequently a secondary C02 diffusion. Recently, SHIMOUCHI et al (1984) found that the intracellular Pco, change following the HC03-shift could be determined by using both the modified Henderson-Hasselbalch equation and the relation between the changes in buffer base and intracellular pH.…”

mentioning

confidence: 99%

Numerical solution of partial differential equations for CO2 diffusion accompanying HCO3- shift in red blood cells.

Kagawa¹,

Mochizuki²

1984

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A computer program for a numerical solution of the C02 diffusion in the red blood cell including the HC03-shift was developed. Comparing the calculated extracellular Pco 2 curve with the experimental data on the primary and secondary C02 diffusions, the permeabilities of C02 and HC03-across the red cell membrane, i2(C02) and i(HC03-), were determined as i2(C02)=2.5 x 10-6 cm/(sec . Torr), Inward i(HC03-) =5 x 10-4 cm/sec , Outward ~(HC03-)=7 x 10-4 cm/sec. The dependencies of the C02 diffusion rate on the hematocrit and initial intraand extracellular HC03-concentrations were examined using the above permeabilities. The half-time of the extracellular PC02 change in a closed RBC suspension was obviously reduced as the hematocrit and initial extracellular HC03-increased, while the effect of the initial intracellular HC03-was not significant. The C02 diffusion in vivo was simulated using pulmonary and tissue capillary models. The half-time of the extracellular HC03-change was about 0.15 sec, while that of the intracellular HC03-change ranged from 40 to 60 msec. Despite the considerable interest in the interaction of CO2 and 02 diffusions into and out of the red blood cells (RBC), the C02 diffusion process into the RBC has not been explained theoretically. Insofar as the two compartment model (HILL et al., 1973;FORSTER and CRANDALL, 1975) was used, the above interaction cannot be calculated. KERNOHAN et al. (1963) reported that the C02 hydration and dehydration reactions occur so fast in the RBC that the chemical equilibrium is established within 1 msec. Therefore, because the intracellular Pco2 change is mainly limited by the C02 and HC03-diffusions, we attempted to solve the differential equations for the diffusion numerically in a disc RBC model. In an effort to obtain a numerical solution, NIIZEKI et al. (1983) measured the diffusion rate of C02 in the RBC in a closed RBC suspension. In their experiment on the