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  • 1
    Electronic Resource
    Electronic Resource
    Mechanism of action of aldosterone on active sodium transport across toad skin (1980)
    Springer
    Pflügers Archiv 385 (1980), S. 181-187 
    Details
    ISSN: 1432-2013
    Keywords: Sodium transport ; Aldosterone ; Intracellular measurements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 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 (≥0.1 μM). 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647455
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  • 2
    Electronic Resource
    Electronic Resource
    Contribution of junctional conductance to the cellular voltage-divider ratio in frog skins (1983)
    Springer
    Pflügers Archiv 399 (1983), S. 336-341 
    Details
    ISSN: 1432-2013
    Keywords: Frog skin ; Junctional conductance ; Voltagedivider ratio ; Paracellular conductance ; Membrane conductances
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It has been suggested that distribution of lateral interspace resistance in association with a highly conductive junction can significantly affect the measurement of outer membrane(o)/epithelial(t) voltage divider ratios (F o=δV o/δV t), thereby leading to erroneous inferences regarding the outer membrane fractional resistance [fR o=R o/R c=R o/(R o+R i)], whereR o andR i are the outer and inner cell membrane resistance respectively andR c is the total cell membrane resistance. We present here experimental evidence for this point of view. During seasons when frog skins were highly permeable to Cl, transepithelial conductanceg t often exceeded 2 mS/cm2. High concentrations of external amiloride rapidly blocked cellular transport, butg t initially remained high andF o remained appreciably less than 1.0. These values ofF o were found here to result from low junctional resistanceR j: increase ofR j, either gradually following the administration of amiloride, or abruptly with external replacement of Cl by other anions, was associated with increase ofF o to near unity, without effect on the membrane potential or significant change in the short-circuit current. Experimental results following amiloride validated a simple equivalent circuit model predicting near-linear increase inF o with progressive decrease ing t and led to plausible values ofR j and lateral space resistanceR l. The possible influence of the paracellular resistance pattern on the evaluation of cell membrane resistances from voltage divider ratios is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00652761
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  • 3
    Electronic Resource
    Electronic Resource
    K+-permeability of the outer border of the frog skin (R. temporaria) (1980)
    Springer
    The journal of membrane biology 52 (1980), S. 107-113 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Skins fromRana 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869115
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanism of stimulation by epinephrine of active transepithelial Cl transport in isolated frog cornea (1980)
    Springer
    The journal of membrane biology 56 (1980), S. 73-79 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In the isolated frog cornea, the effects of 0.1mm epinephrine were measured on both the transepithelial and intracellular electrical parameters. Epinephrine increased the short-circuit current (I sc) and transepithelial electrical conductance (g t) by 176 and 96%, respectively. The effective electromotive driving force for active transepithelial Cl transport (E Cl) was 45 mV and agrees with the value forE Cl calculated by a different technique in the isolated rabbit corneal epithelium (Klyce, S.D., Wong, R.K.S., 1977,J. Physiol. (London) 266: 777). With respect to the tear-side bathing solution, epinephrine caused the intracellular potential difference of shortcircuited frog corneas to decrease from −54 to −50 mV (P〉0.05). The fractional resistance of the apical membrane {F(R o)=(Ro/Ro+Ri)} whereR o andR i represent the resistances of the apical and basolateral membranes, respectively, decreased from 0.38±0.06 to 0.23±0.03. Using these values ofF(R o) and the cellular conductances, the calculated Cl resistances ofR o andR i decreased 4.3- and 2.3-fold, respectively. However, the value forE Cl calculated from the intracellular electrical measurements (48 mV) did not appear to change since this value was in close agreement with the value forE Cl calculated from the effects of epinephrine on the transepithelial electrical parameters. Thus, the effects of epinephrine onI sc andg t can be accounted for by increases in the Cl conductance of both the apical and basolateral membranes. Epinephrine caused the potential difference across the basolateral membrane to hyperpolarize by 9 mV. All of these results are consistent with the notion that the steps in transepithelial Cl transport include uphill movement into the cell across the basolateral membrane followed by downhill movement across the apical membrane into the tear-side bathing solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869354
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  • 5
    Electronic Resource
    Electronic Resource
    Electrophysiologic changes associated with potassium depletion of frog skin (1980)
    Springer
    The journal of membrane biology 57 (1980), S. 235-241 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Skins from the frogRana 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 (V SC), fractional resistance (FR), short-circuit current (I SC) and total tissue conductance (g T) were constantly monitored during impalements of the epithelial cells. The mean value (±se) forV SC 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 11/2 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869591
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  • 6
    Electronic Resource
    Electronic Resource
    Relationship of transepithelial electrical potential to membrane potentials and conductance ratios in frog skin (1982)
    Springer
    The journal of membrane biology 69 (1982), S. 125-136 
    Details
    ISSN: 1432-1424
    Keywords: membrane potentials ; membrane conductances ; frog skin ; constant field equation ; sodium conductances
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Previous studies in anuran epithelia have shown that, after clamping the transepithelial voltage in symmetrical sequences for 4–6 min there is near-constancy of the rate of active Na transport and the associated oxidative metabolism, with a near-linear potential dependence of both. Here we have investigated in frog skin the cellular electrophysiological events associated with voltage clamping (V t =inside-outside potential). Increase and decrease ofV t produced converse effects, related directly to the magnitude ofV t . Hyperpolarization resulted in prompt decrease in inward transepithelial currentI t and increase in fractional outer membrane resistancefR 0 (as evaluated from small transient voltage perturbations) and in outer membrane potentialV 0. Overshoot ofV 0 was followed by relaxation to a quasi-steady state in minutes. Changes infR 0 were progressive, with half times of some 1–5 sec. Changes in transepithelial slope conductanceg t were more variable, usually preventing precise evaluation of the outer and inner cell membrane conductancesg 0 andg i . Nevertheless, it was shown thatg 0 is related inversely toV t andV 0. Presuming insensitivity ofV i toV t , the dependence ofg 0 onV 0 in the steady state much exceeds that predicted by the constant field equation. Apparent inconsistencies with earlier results of others may be attributable to differences in protocol and the complex dependence ofg 0 onV 0 and/or cellular current. In contrast to previous findings in tight epithelia at open circuit, differences inV t were associated with substantial differences infR 0 and inner membrane potentialV i . Hyperpolarization ofV t over ranges commonly employed in studies of active transport and metabolism appears to increase significantly the electrochemical work per Na ion transported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01872272
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