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Biomedical subjects

W Nagel

Publications and source records attributed to W Nagel.

At least 109 records · Page 6Linked to original sources
PubMed1981

Intracellular ionic activities in frog skin.

Intracellular Na+, K+, and Cl- activities (aiNa, aiK, aiCl) and transapical membrane potentials (V0) were measured with liquid ion-exchanger and open-tip microelectrodes in isolated short-circuited frog skins (R. pipiens) incubated at 23 degrees C in normal amphibian Ringer's solution. Under control conditions aiNa = 14 +/- 3 mM, aiK = 132 +/- 10 mM and aiCl = 18 +/- 3 mM (SD). The value of aiCl is 4.4 times the value corresponding to electrochemical equilibrium for this ion. Thus, Cl- is actively accumulated by epithelial cells of the frog skin. Shortly after addition of amiloride (2--5 microM) to the apical bathing medium, aiK, aiNa, and aiCl were essentially unchanged although V0 had hyperpolarized by about 30--40 mV. During long-term exposure to amiloride aiK and aiCl did not change significantly, V0 depolarized by about 16 mV from the maximal value and aiNa decreased to 8 +/- 3 mM. Immediately after exposure to amiloride the transmembrane driving force for Na+ increased from 124 to 154 mV. During further exposure to amiloride, despite changes in both V0 and aiNa, this driving force remained virtually constant. Since Isc during this period was close to zero, it is suggested that the observed driving force for Na+ under these condition approximates the maximal driving force generated by the Na+--K+ ATP-ase pump in the basolateral cell membrane.

Amiloride↗
PubMed1980

Electrophysiologic changes associated with potassium depletion of frog skin.

Skins from the frog Rana pipiens pipiens were studied under short-circuited conditions during the course of removing and replacing potassium in the inner bathing media in 14 experiments. The intracellular potential (Vsc), fractional resistance (FR), short-circuit current (Isc) and total tissue conductance (gr) were constantly monitored during impalements of the epithelial cells. The mean value (+/- SE) for Vsc was --79 (+/- 3) mV under baseline conditions. Removal of potassium from the inner bathing solution transiently stimulated the short-circuit current and hyperpolarized the basolateral membrane; with sufficiently long incubations, the basolateral membrane was eventually depolarized. Restoration of potassium to the inner solution within 43 min after initiating the perfusion with K+-free solution depolarized the basolateral membrane. However, restoration of potassium after at least 1 1/2 hr of incubation hyperpolarized the membrane. Ouabain consistently depolarized the basolateral membrane, even after extended periods of potassium depletion as long as 320 min. In the presence of ouabain, restoration of potassium depolarized the basolateral membrane. The data provide further evidence for the concept that the Na--K exchange pump of frog skin is rheogenic. Furthermore, the results suggest that the pump continues to be active even during prolonged periods of potassium depletion, reaccumulating potassium which has leaked out of the epithelial cells.

Animals↗
PubMed1980

Mechanism of action of aldosterone on active sodium transport across toad skin.

Epithelium of the abdominal skin of the toad, Bufo marinus, has been studied by microelectrode impalement. Using an electrical equivalent circuit model, effective EMF's and specific conductances of the apical and basolateral membrane could be calculated. The skin was divided into 2 fragments for incubation in the presence, or not, of aldosterone (greater than or equal to 0.1 microM). After incubation overnight, sodium transport by the hormone-treated piece was increased 2.7-fold on average, compared to the untreated control. Concomitantly, conductance of the apical border increased more than 3-fold. Furthermore, mean conductance and electromotive force at the basolateral border increased by 80% and by 10%, respectively. Whether the latter changes merely represent delayed adaptation to increased apical conductance, cannot be settled from the data available.

Aldosterone↗
PubMed1980

K+-permeability of the outer border of the frog skin (R. temporaria).

Skins from Rana temporaria, investigated with microelectrode techniques in the absence of Na uptake across the outer border (Na-free epithelial solution or amiloride), were found to be permeable to K+ at the apical membrane in 10-20% of the experiments. Full development of the K+-permeable state requires the absence of Na+ uptake for certain periods of time, which suggests that the K+-permeability of the apical membrane is higher at lower intracellular [Na]. The addition of Ba++ reduces the K+-permeability of the apical membrane. These skins may provide a model for the study of transcellular K+ movements.

Amiloride↗
PubMed1980

Time course of pump inhibition by ouabain in amphibian epithelia.

Inhibition by ouabain of rheogenic Na+ transport across the basolateral membranes of frog skin is found to be manifest within 3-4 min. This rate of pump inhibition is not different from the rate of diffusion through extracellular tissue layers between the serosal bath and the actual site of action, i.e., the epithelial cell layers. It is concluded that the well-known slow time course of decrease in transepithelial current flow is due to ionic redistribution and conductance changes of the epithelial membranes secondary to pump inhibition.

Animals↗
PubMed1980

Rheogenic sodium transport in a tight epithelium, the amphibian skin.

1. Intracellular potentials from frog and toad skins were measured to identify rheogenic components of active Na transport across the basolateral membrane. Transcellular current flow and associated R . I-drops were blocked with amiloride or Na-free mucosal solution. 2. The potential difference across the basolateral membrane was found to be hyperpolarized by 18 . 5 +/- 1 . 6 mV above the steady-state value immediately after blockage of apical membrane Na conductance. The hyperpolarization disappeared within 15--25 min. 3. The final steady-state value of 93 . 1 +/- 2 . 5 mV was slightly less than reasonable estimates of the K equilibrium potential. 4. The hyperpolarization could not be observed 3--5 min after addition of ouabain (10(-4) M). 5. Both the magnitude and duration of the hyperpolarization correlate directly with the amount of Na accumulated in the intracellular space. 6. A fraction of the intracellular potential was missing when Na transport was re-established after long term blockage of apical membrane Na entry. It reappeared within 10--20 min. 7. It is suggested that the hyperpolarization is due to rheogenic Na transport across the basolateral membranes. This transport mechanism may contribute some 30--50% of the electrical gradient for passive Na entry across the mucosal membrane. 8. A coupling ratio between pumped fluxes of Na and K of about 2:1 is calculated from the data.

Animals↗
PubMed1979

Inhibition of potassium conductance by barium in frog skin epithelium.

The effect of Ba2+ (0.5 mM, corial side) upon the transport characteristics of the frog skin epithelium was investigated. It was observed that Ba2+ decreased the conductance of the preferably K+-permeable basolateral border to less than 30% of its control value. Furthermore, Ba2+ abolished the K+ electrode-like behaviour, existing at the basolateral membrane under conditions of zero transcellular current flow, for [K+] below 10--15 mM. Effects upon other parameters of transepithelial transport (electromotive forces and resistance of outer or basolateral border and shunt pathway, respectively) were small and might represent secondary events. It is concluded that Ba2+ inhibits passive fluxes of K+ across basolateral membranes of tight, Na+ transporting epithelia, similar to its influence upon membranes of nonpolar cells.

Amiloride↗
PubMed1979

Ouabain on active transepithelial sodium transport in frog skin: studies with microelectrodes.

Studies were done with isolated frog skin to determine the effects of 10(-4) M ouabain on the electrophysiological parameters of outer and inner barriers of the Na-transporting cells. Microelectrodes were used to impale the skins from the outer surface to determine the intracellular voltages (Vsco) under conditions of short-circuiting and under conditions where a voltage clamp was used to vary the transepithelial voltage, VT. From this, the electrical resistances of outer (Rfo) and inner (RI) barriers were estimated. In addition, the driving force for active transepithelial Na transport (ENa = E'1) was estimated from the values of VT when the Vo = 0 mV (Helman and Fisher. 1977. J. Gen. Physiol. 69: 571-604). Studies were done with skins bathed with the usual 2.4 meq/liter [K]i in the inner solution as well as with reduced [K]i of 0.5 and 0 meq/liter. Characteristically, the responses to ouabain could be described by an initial rapid phase (5-10 min) during which time the Ri was increased markedly and the E'1 was decreased from control values. Thereafter, during the slow phases of the response, the resistances of both outer and inner barriers increased continuously and markedly with time leading ultimately to essentially complete inhibition of the short-circuit current. Similar studies were done with skins exposed to 10(-4) M amiloride in the outer solution. Although estimates of Ri could not be obtained under these conditions, the effects on the Vsco and E'1 were similar to those observed for the Na-transporting skins. However, the magnitudes of the effects were less and relatively slower than observed for the Na-transporting skins. The results of these studies were analyzed within the context of a proposed electrical model that takes into account the observation that the magnitude of the voltage at the inner barrier appears to exceed the equilibrium potential for K especially when transepithelial Na transport is inhibited at the apical barrier of the cells.

Action Potentials↗
PubMed1978

Effects of antidiuretic hormone upon electrical potential and resistance of apical and basolateral membranes of frog skin.

The effect of ADH upon the intracellular potential and the resistance of inner and outer borders of the transport pathway was investigated on isolated skins of Rana temporaria. Within 40 min after ADH (100--300 mU/ml), the intracellular potential under short-circuit conditions decreased to about 40% of the control value (--79 +/- 4 mV), concomitant with an increase in the short-circuit current to about 160% of the control value. Amiloride, applied when steady values under ADH had been reached, caused an immediate rise of the intracellular potential to values typical for control conditions. This confirms (i) the intracellular location of the microelectrode and the absence of impalement artifacts, and (ii) the ineffectiveness of ADH upon the electromotive forces of the inner border. ADH had no effect upon the intracellular potential after blockage of the Na entry by Amiloride. The equilibrium potential of the outer border was estimated to be about +20mV under the influence of ADH. As this value is considerably less positive than might be expected for the chemical potential of Na, a significant contribution of ions other than Na to the outer border conductance and equilibrium potential is implicated. The resistance of the outer border was more significantly decreased than that of the active transcellular pathway after ADH due to an increase in the inner border resistance, which exceeded that of the outer border after ADH. The effect of ADH upon the outer membrane characteristics would be underestimated by a factor of two, if the alterations of the electrical potential difference were not taken into consideration.

Amiloride↗