title: Fluctuation analysis of short-circuit current in a warm-blooded sodium-retaining epithelium: site current, density, and interaction with triamterene.
abstract: Density and conductance of the Na-site in hen coprodeum were studied by employing fluctuation analysis of short-circuit current at sodium concentrations from 26 to 130 mM. Fluctuations of current in the frequency range 2-800 Hz were induced by triamterene, a reversible blocker of conducting epithelial Na-sites. At 130 mM Na the site density was 5.8 +/- 1.0 micrometer-2 and the site conductance was 4 pS. This conductance is equal to that of the frog skin (W. Van Driessche and B. Lindemann, 1979, Nature (London) 282:519-520). Extrapolation of site density to zero sodium renders a total of 38 +/- 28 sites micrometer-2, which is compared with other estimates for the coprodeum. The site-triamterene association and dissociation constants were 9.5 +/- 0.4 rad sec-1 micrometer-1 and 255 +/- 20 rad sec-1 and they were independent of external sodium concentration. An analysis of the affinity constant for triamterene based on the DC-short-circuit current was found to be unrelated to the external sodium concentration and identical to that obtained from fluctuation analysis indicating a noncompetitive interaction between sodium and triamterene. Due to the oxygen demand of the epithelium we have developed an experimental method using short data processing times. A new analytical approach using integration of the power density spectrum proved necessary because of low signal-to-noise ratios.
mesh_terms: D000818:Animals; D002645:Chickens; D004848:Epithelium / Q000378:metabolism*; D005260:Female; D007422:Intestines / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D012964:Sodium / Q000378:metabolism*; D014223:Triamterene / Q000494:pharmacology*
chemical_list: D007473:Ion Channels; D012964:Sodium; D014223:Triamterene