Cyst function in polycystic kidney disease: nongradient cysts

Previous studies from this laboratory have demonstrated active sodium transport by cyst epithelia obtained from human polycystic kidneys. Cysts which maintained a steep sodium gradient between cyst fluid and plasma (gradient cysts) exhibited conductive amiloride sensitive sodium transport. Cysts which failed to maintain a sodium gradient between cyst fluid and plasma (nongradient cysts) were insufficiently characterized. In the present study, we report flux and electrical parameters of 23 nongradient cysts studied in vitro. Nongradient cysts exhibit low PD, low Isc, and high conductance. Unidirectional fluxes of sodium and chloride varied from approximately 14.4 to greater than 250 microEq.h-1.cm-2 and net flux was not significantly different from zero. There was no apparent effect on flux or electrical parameters of amiloride, ouabain, acetazolamide, or bumetanide. There was a very high correlation between unidirectional flux of sodium and chloride in individual cysts which was similar to the predicted relationship for diffusional fluxes. This correlation suggested that movement of sodium and chloride across cyst membranes was passive via an aqueous channel. Estimates of ionic permeability exceeded those determined for proximal nephron by almost one order of magnitude. We conclude that nongradient cysts are nonfunctional and, regardless of their origin, do not function analogously to the proximal nephron.