Electrophysiologic changes associated with potassium depletion of frog skin

Abstract

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.

Voltage dependence of current through the Na,K-exchange pump ofRana oocytes

“…Depending on the parallel membrane conductance, increased turnover of the pump can certainly hyperpolarize some cells significantly (e.g., Nagel et al, 1980), thereby activating or inactivating parallel voltage-dependent processes. Perhaps more importantly, the voltage sensitivity may permit the pump to respond rapidly to changes in the external environment, which would otherwise be detected much more slowly and indirectly through changes in the intracellular activities of Na + and K +.…”

Microelectrode study of K+ accumulation by tight epithelia: I. Baseline values of split frog skin and toad urinary bladder

“…This problem was solved by transiently superfusing the inner surface with depolarizing agents, whose mechanism of action is known. Both strophanthidin and ouabain act by inhibiting the electrogenic or rheogenic Na § K + exchange pump at the basolateral membrane (Helman, Nagel & Fisher, 1979;Nagel, 1980;Nagel et al, 1980); however, in contrast to the prolonged duration of action of the cardiac glycoside, the effect of the aglycone on the basolateral membrane potential is rapidly reversible (Fig. 3).…”

Transepithelial Na+ transport and the intracellular fluids: A computer study

“…Electron microprobe measurements of intracellular chloride concentration in toad bladder (Rick et al, 1978b;Civan et al, 1980) and frog skin (Rick, DiSrge, Arnim & Thurau, 1978a), electrometric determinations of intracellular chloride activity in frog skin (NageI, Garcia-Diaz & Armstrong, in press), and intracellular measurements of membrane potential in frog skin (Nagel, 1976(Nagel, , 1980Helman & Fisher, 1977;Helman, Nagel & Fisher, 1979;Nagel, Pope, Peterson & Civan, 1980) suggest that these tight epithelia accumulate intracellular C1-against an electrochemical gradient. In principle, such accumulation could proceed by coupling directly to a source of metabolic energy or indirectly through a symport or antiport mechanism to flows of other diffusible moieties.…”

“…Another set of initial baseline values was entered for the second set of parameters: It, V" and V bz (e.g., Nagel, 1976;Fr6mter & Gebler, 1977;Helman & Fisher, 1977;Nagel et al, 1980) andcK, ..... eN~ , c~, % andv c (Macknight, DiBona, Leaf &Civan, 1971;Macknight, Civan & Leaf, 1975a, b;Rick etal., 1978b;Civan et al, 1980). All of these parameters were subject to change in response to the experimental perturbations introduced during later periods of the computer simulation.…”