AJP - Renal Physiology, Vol 249, Issue 3 424-F431, Copyright © 1985 by American Physiological Society
Active transport and exchange diffusion of Cl across the isolated skin of Rana pipiens
K. Drewnowska and T. U. Biber
Transepithelial Cl influx and efflux were measured in pairs of frog skin
(Rana pipiens) matched according to short-circuit current, tissue
conductance, and transepithelial potential (TEP). The skins were bathed
symmetrically in NaCl Ringer and voltage clamped at TEP values ranging from
-60 to +60 mV. At 0 TEP, Cl influx and net inward Cl movement (in neq X h-1
X cm-2) were, respectively, 961 +/- 116 and 463 +/- 68 in NaCl Ringer, 509
+/- 52 and 202 +/- 53 in amiloride-treated skins, 4,168 +/- 777 and 1,444
+/- 447 in theophylline-treated skins, and 587 +/- 38 and 97 +/- 44 in
Na-free Ringer. A correlation was discovered between short-circuit current
and Cl fluxes corresponding to a 2:6:1 relationship between changes in
active Na transport and active Cl transport. Deviations from the predicted
Cl flux ratio indicate the presence of exchange diffusion in the range of
spontaneously occurring TEPs, in contrast to observations on R. temporaria
and R. esculenta. The experiments indicate that a substantial portion of
transepithelial Cl movement proceeds transcellularly 1) via active Cl
transport that is Na dependent, amiloride sensitive, stimulated by
theophylline, and apparently correlated with active Na transport, and 2) by
means of exchange diffusion that not only occurs under short-circuit
conditions but also at positive TEPs. It is possible to explain both the
exchange diffusion and the properties of active Cl transport by a Cl-HCO3
exchange system at the apical side of the transporting cell that interacts
with a Na-H exchange mechanism, a notion consistent with the recent
observation of an amiloride-induced decrease in intracellular pH.
