Na+ and K+ cell concentrations in collagenase-treated rat kidney tubules incubated at various temperatures.

Na+ and K+ cell contents were measured in single pieces of tubule (0.4-0.8 mm/sample) micro-dissected from the outer medulla of collagenase-treated rat kidney tissue. Extracellular cations were washed out by rinsing the tubules in ice-cold choline-chloride solution. Na+ and K+ cell contents were measured by emission flame microphotometry after appropriate treatment of the samples. Tubular volumes were calculated from photographic pictures taken before (at 4 degrees C) and after incubation of the samples. Medullary collecting tubules (MCT) and medullary thick ascending limbs of Henle (MAL) were used in this study. When kept at 4 degrees C for 2 h or more, Na+ and K+ concentrations (meq/l cell volume) were 86.3 and 30.6, respectively, in MCT and 16.2 and 94.3, respectively, in MAL. After about 5 min of incubation at 30 degrees C, MCT samples inverted their cation contents up to new steady-state concentrations (Na+ 17.4 and K+ 97.5). During incubation, the volume of MCT samples decreased slowly and in an exponential way, the rate of which was highly temperature dependent. Na+ and K+ cell concentrations in such incubated MCT samples, however, remained fairly constant between 20 and 37 degrees C. In contrast, when MAL samples were incubated at 30 degrees C, Na+ and K+ concentrations (15.9 and 90.4, respectively) remained equal to those measured at 4 degrees C and no change in volume was observed in MAL samples.