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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Influx and efflux of sodium at the outer surface of frog skin (1975)
    Springer
    The journal of membrane biology 22 (1975), S. 183-196 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The unidirectional Na influx,j 12, and Na efflux,j 21, at the epithelial surface of the frog skin were determined under various experimental conditions. Thej 21 was taken as the difference betweenj 12 and the simultaneously measured shortcircuit current (SCC). Errors inj 12 determination originating from various transport rates within the skin were kept to a minimum using a normalization procedure. Under control conditions,j 12 (1.20 μEquiv/cm2·hr) was found to be only slightly larger than the SCC (1.10 μEquiv/cm2·hr). After inhibition of the transepithelial Na transport by amiloride, ouabain, low temperature and low Na concentration, the reduction ofj 12 and SCC was almost identical, indicating that the entrance of Na into the epithelium is rate limiting for the transepithelial transport. Compared to the control,j 21 remained unchanged after amiloride and ouabain, but was insignificantly reduced at low temperature and significantly reduced at low Na concentration. These data are consistent with the assumption that the Na efflux follows mainly an extracellular pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868170
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of lithium upon the intracellular potential of frog skin epithelium (1977)
    Springer
    The journal of membrane biology 37 (1977), S. 347-359 
    Details
    ISSN: 1432-1424
    Keywords: Frog skin ; intracellular potential ; lithium ; sodium transport ; amiloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effect of Li upon the intracellular potential of frog skin (Rana esculenta) was investigated. In the range between 1 and 25mm Li in the epithelial bathing solution, a semilogarithmic linear relationship between [Li] and intracellular potential under short circuit conditions was obtained. The intracellular potential at all [Li] is quantitatively sufficient to explain the previously reported accumulation of Li in the intracellular space of the frog skin epithelium (Leblanc, G. 1972.Pfluegers Arch. 337:1) on the basis of a passive entrance step at the outer border. A reduction of the intracellular potential by Li is also observed in the presence of 6mm Na in the epithelial bathing solution. Consequences regarding the mechanism of uptake of Na across the outer border of the frog skin are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01940939
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Implications of an anomalous intracellular electrical response in bullfrog corneal epithelium (1985)
    Springer
    The journal of membrane biology 87 (1985), S. 201-209 
    Details
    ISSN: 1432-1424
    Keywords: corneal epithelium ; frog ; chloride transport ; potassium conductance ; apical and basolateral membranes ; barium ; ouabain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The ionic dependencies of the transepithelial and intracellular electrical parameters were measured in the isolated frog cornea. In NaCl Ringer's the intracellular potential differenceV sc measured under short-circuit conditions depolarized by nearly the same amount after either increasing the stromal-side KCl concentration from 2.5 to 25mm or exposure to 2mm BaCl2 (K+ channel blocker). With Ba2+ the depolarization of theV sc by 25mm K+ was reduced to one-quarter of the control change. If the Cl-permselective apical membrane resistanceR o remained unchanged, the relative basolateral membrane resistanceR i, which includes the lateral intercellular space, increased at the most by less than twofold after Ba2+. These effects in conjunction with the depolarization of theV sc by 62 mV after increasing the stromal-side K+ from 2.5 to 100mm in Cl-free Ringer's as well as the increase of the apparent ratio of membrane resistances (a=R o/Ri) from 13 to 32 are all indicative of an appreciable basolateral membrane K+ conductance. This ratio decreased significantly after exposure to either 25mm K+ or Ba2+. The decline ofR o/Ri with 25mm K+ appears to be anomalous since this decrease is not consistent with just an increase of basolateral membrane conductance by 25mm K+, but rather perhaps a larger decrease ofR o thanR iAlso an increase of lateral space resistance may offset the effect of decreasingR i with 25mm K+. In contrast,R o/Ri did transiently increase during voltage clamping of the apical membrane potential differenceV o and exposure to 25mm K+ on the stromal side. This increase and subsequent decrease ofR o/Ri supports the idea that increases in stromal K+ concentration may produce secondary membrane resistance changes. These effects onR o/Ri show that the presence of asymmetric ionic conductance properties in the apical and basolateral membranes can limit the interpretative value of this parameter. The complete substitution of Na+ withn-methyl-glucamine in Cl-free Ringer's on the stromal side hyperpolarized theV sc by 6 mV whereas 10−4 m ouabain depolarized theV sc by 7 mV. Thus the basolateral membrane contains K+, Na+ and perhaps Cl− pathways in parallel with the Na/K pump component.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871219
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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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  • 7
    Electronic Resource
    Electronic Resource
    Effects of antidiuretic hormone upon electrical potential and resistance of apical and basolateral membranes of frog skin (1978)
    Springer
    The journal of membrane biology 42 (1978), S. 99-122 
    Details
    ISSN: 1432-1424
    Keywords: Frog skin ; Na transport ; ADH ; outer border effective emf ; transcellular resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary 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 ofRana 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 +20 mV 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01885366
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Effect of Loop Diuretics on Bullfrog Cornea Epithelium (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 574 (1989), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1989.tb25185.x
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  • 10
    Electronic Resource
    Electronic Resource
    Intercellular junctions of frog skin epithelial cells (1976)
    [s.l.] : Nature Publishing Group
    Nature 264 (1976), S. 469-471 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Abdominal skins of R. temporaria and R. esculenta were punctured from the epithelial side perpendicular to the surface. The epithelium was properly attached to a copper grid at the corial side by a negative pressure of 30cm H2O. Trans-epithelial potential difference (PDtr) and short circuit ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/264469a0
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