| Abstrakt: |
Summary The operation of the multicompartmental frog skin epidermal model 10E described in the preceding paper was tested to find out by computer simulation whether it responds to changes in [Na+] in the same manner as frog skin. In the range from 5 to 115mm [Na+]0, the rate of net Na+ flux across skin is known to increase. The results can be fitted to Michaelis-Menten's law of reaction kinetics, or, alternately, to Hoshiko's linear function, plotting fluxvs. log [Na+]0. Model 10E simulated the laboratory results on skin, provided that the rate coefficients at the site of entry of Na+ into the system were varied in exactly the same manner as they actually were found to vary in skin. In model studies, Na+ backflux (outflux) decreased with increasing [Na+]0, contrary to observations on skin. This discrepancy may be related to adaptive reactions in skins (decrease in permeability) when [Na+]0 is lowered, a feature that has not been modeled. It is known that the skin p.d. changes, mostly, by approximately 35 mV per decade change in [Na+]0. Model 10E gave very nearly the same result when the rate coefficients for entry of Na+ were changed as mentioned above (i.e., varied exactly as they were found to vary in skin). Skin and model 10E behaved similarly in that, at [Na+]0=[Na+]i=115mm, the extent to which labeling with Na* from the outside (12%) and from the inside (88%) is possible was the same. Model data are presented which show in which way the Na+ pools, [Na+] in the individual compartments, and intercompartmental fluxes changed with changing [Na+]0. Because of lack of experimental data on skin for comparison, these calculated results are purely hypothetical, but they are not unreasonable. |
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