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Biomedical subjects

R Casteels

Publications and source records attributed to R Casteels.

At least 217 records · Page 12Linked to original sources
PubMed1971

The distribution of chloride ions in the smooth muscle cells of the guinea-pig's taenia coli.

1. The intracellular Cl concentration of taenia coli cells, determined by an analytical procedure and by an extrapolation procedure, has a value between 60 and 73 m-mole/l. cell water.2. This concentration is too high to be explained by a passive distribution. The discrepancy could be due to a binding of Cl in the intracellular or extracellular compartment or to an active uptake of Cl by the cells.3. Determination of the activity coefficient for Cl in homogenates of smooth muscle did not support the hypothesis of binding of Cl ions.4. The efflux of (36)Cl from taenia coli cells was not affected by foreign anions. After 1 hr exposure to a Cl-free solution, the tissues contained less than 1 m-mole of Cl/kg wet wt., even if Cl had been replaced by a slowly penetrating anion. Because the intracellular cation concentration remained constant, it has to be assumed that new anionic groups can be formed in the cells.5. The intracellular Cl concentration decreases during exposure to ouabain or to K-free solution. The uptake seems therefore to be linked to the uptake of K through the Na pump.6. Exposure to K-free solution increases the K permeability of the membrane. Under the same experimental conditions the Cl permeability of the membrane increases as long as K is leaking out of the cells.7. The anions in the external solution exert an important influence on the K permeability of the membrane. NO(3) and I cause a small increase of the permeability and large anions such as benzenesulphonate, propionate or pyroglutamate cause a pronounced decrease of this permeability.

Animals↗
PubMed1971

Membrane potential of smooth muscle cells in K-free solution.

1. The changes of the ion content, the membrane potential and of the membrane permeability of taenia coli cells have been studied during exposure to K-free solutions. The relative value of the total membrane conductance was determined by measuring the electrotonic potential during constant current pulses with an intracellular electrode. The P(K) values were calculated from (42)K-efflux in K-free solutions.2. In solutions containing penetrating anions the cells initially depolarize. Thereafter they hyperpolarize to about - 85 mV and again depolarize after 90 min to - 5 mV. These potential changes are much smaller if large anions are used as chloride substitutes. Moreover, the final depolarization is only reached after 4-5 hr. This hyperpolarization is not inhibited by 10(-5)M ouabain.3. These potential changes are accompanied by a progressive exchange of intracellular K by Na. In solutions containing chloride or nitrate the relative value of the total membrane conductance increases to a maximal value, corresponding to the peak value of the calculated P(K). Such changes of the membrane conductance and of P(K) do not occur in K-free solutions containing large anions.4. It is proposed that the initial depolarization is probably caused by an inhibition of an electrogenic Na pump. In chloride or nitrate solution the hyperpolarization is due to an increase of the [K](i)/[K](o) ratio and to an increase of the K permeability. In the presence of large anions the hyperpolarization remains small because this increase of P(K) does not occur.

Animals↗
PubMed1971

Electrogenic sodium pump in smooth muscle cells of the guinea-pig's taenia coli.

1. The changes of the membrane potential, of the K equilibrium potential, and of the membrane conductance during K accumulation by K-depleted tissues have been studied. Three subsequent characteristic periods can be described.2. Readmission of 5.9 mM-K after complete depletion results in a rapid extrusion of Na and uptake of K, and in a rapid hyperpolarization of the cells. Initially the time course of the K equilibrium potential and the membrane potential are similar except in propionate solution. This initial period is characterized by a high membrane conductance. No change of membrane potential occurs if 10(-5)M ouabain is present.3. After 5-7 min the membrane potential becomes more negative than the K equilibrium potential. The difference between both values is larger in solutions containing propionate or in hypertonic solutions. This second phase of the recovery period is characterized by a progressive decrease of the membrane conductance.4. In a third phase both the membrane potential and the membrane resistance return to their steady-state value.5. If the external K concentration in the recovery solution is increased, the maximal hyperpolarization is less and has a shorter duration. A decrease of the temperature of the recovery solution results in a slower initial rate of repolarization and in a decrease of the maximal value of the hyperpolarization.6. These observations demonstrate the existence of an electrogenic sodium pump in smooth muscle cells during stimulation of the Na pump. An analysis of the experimental data obtained under steady-state conditions in normal Krebs solution suggests that also under these conditions an electrogenic Na pump might take part in the maintenance of the resting potential.

Animals↗
PubMed1969

Calculation of the membrane potential in smooth muscle cells of the guinea-pig's taenia coli by the Goldman equation.

1. The intracellular K(+), Cl(-) and Na(+) concentrations in the taenia coli cells of the guinea-pig have been estimated from the total ion content or the extrapolated intracellular tracer content, the sorbitol space and the dry wt./wet wt. ratio.2. The exchange of K(+), Cl(-) and Na(+) was studied by following the uptake and the efflux of these ions with radioactive isotopes. The following efflux values have been calculated: m(K), 4 p-mole.cm(-2).sec(-1); m(Cl), 8.4 p-mole.cm(-2).sec(-1) and m(Na), 7.2 p-mole.cm(-2).sec(-1). These flux values agree well with the influx values, obtained under the same experimental conditions.3. The slowness of diffusion in the extracellular space reduces the Na flux by about 2.5% and the K flux by about 30%. A correction factor of 1.3 has to be introduced to obtain the true K flux.4. The values for the permeability constants calculated by the constant field assumptions are for P(K), 11 x 10(-8) cm/sec; P(Cl), 6.7 x 10(-8) cm/sec and for P(Na), 1.8 x 10(-8) cm/sec. The introduction of these values and of the ion concentrations in the Goldman equation gives a resting potential of -37 mV.5. One of the possible explanations for the discrepancy between the measured resting potential and the calculated one, is that the resting potential of these smooth muscle cells is partly a diffusion potential and partly due to the operation of an electrogenic Na pump.

Animals↗
PubMed1968

Membrane potential and ion content in cat and guinea-pig myometrium and the response to adrenaline and noradrenaline.

1. Cats, virgin and 17 days pregnant, and guinea-pigs, virgin and 14-60 days pregnant, or treated for 1-8 days with oestradiol+progesterone, were used. The response of the uterus to adrenaline and noradrenaline was observed and, in pieces from the same tissues, the resting and active membrane potentials were recorded and the ionic content was determined.2. Adrenaline and noradrenaline relaxed the virgin cat uterus, adrenaline being 20-100 times more potent in vivo and about 10 times or less in vitro.3. Adrenaline and noradrenaline caused contraction of the early pregnant cat uterus, the ratio of potency being about 1.4. Adrenaline and noradrenaline had a biphasic effect on the guinea-pig uterus in all conditions. The ratio of potency was about 1.5. The mean membrane potential was 48 mV in virgin cat uterus and 64 mV on the seventeenth day of pregnancy.6. In guinea-pigs the average membrane potential increased from 38 mV in the virgin uterus to 58 mV on the thirtieth day of pregnancy. A similar increase was produced by eight daily injections of 5 mug oestradiol and, on the last 4 days, additional 1.5 mg progesterone.7. In the cat, no significant change in K and Na content was observed during pregnancy. The intracellular chloride content, however, rose from 51.5 m-moles/1. fibre water in the virgin uterus to 89 m-moles in the early pregnant uterus. As a result, the calculated chloride equilibrium potential changed from - 25 mV in virgin uterus to - 11 mV in pregnant uterus.8. In the guinea-pig no significant change in ion content was observed and the calculated potassium and chloride equilibrium potentials remained both unaltered during pregnancy.9. In contrast to guinea-pig uterus in all conditions, and to virgin cat uterus, early pregnant cat uterus was not spontaneously active and excess calcium caused no hyperpolarization.10. The reversal of the uterine response to adrenaline as a result of pregnancy is discussed in relation to the increase of the intracellular chloride content which was only observed in the cat.

Action Potentials↗