ISSN:
1432-1424
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Relative permeability coefficients (P's) for Li+, Na+, K+, Rb+, Cs+, NH 4 + and Tl+ have been measured in gallbladders of several animal species. Small differences are observed among individual animals of the same species in theP values for a given ion. Individual variations inP values of different ions are closely correlated, permitting construction of so-called selectivity isotherms. Exposure to pH 4 reversibly shiftsP values along the same isotherms as those defined by individual variation. Changes in partial conductances with pH indicate that cation conductance is controlled by acidic sites with an apparent pK a value near 4.5, anion conductance by basic sites with an apparent pK a value below 3. Isotherms for rabbit gallbladder and bullfrog gallbladder are quite similar, and the small differences between them are probably attributable to a narrower permeation channel in rabbit in bullfrog. Permeability ratios for eight other epithelia with leaky “tight junctions” fall close to the isotherms for rabbit and bullfrog gallbladders. The observed isotherms, sequences, and pH-dependence of alkali cation permeability are strikingly consistent with Eisenman's interpretation that selectivity is controlled by site field strength. Variation inP Tl andP NH4 is also correlated with variation in site field strength. Comparison with isotherms or “selectivity fingerprints” for glass electrodes and macrocyclic carriers suggests that the permeation channel in gallbladder tight junctions is highly hydrated; and that sites in the gallbladder may possess net charge and may not be in a precisely regular spatial array.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870092
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