Time dependent and other possible changes of the intracellular D-glucose and Na+ concentration in the cortical tissue of rabbit kidney perfused "in vitro".

The mean intracellular D-glucose concentration (Gi), the ratio between Gi and the serosal extracellular concentration (Gi/Ge) and the cell Na+ (Nai+) were calculated on cortex slices at increasing times after their excision from two groups of kidneys perfused with blood containing 18.1 +/- 0.4 and 23.1 +/- 2.0 mmol.l-1 plasma glucose concentration. The distribution ratios Gi/Ge, always lower than 1, were substantially unchanged up to at least 50s after removal of the tissue from the organ. Between these time limits the calculated Gi and Gi/Ge does not seem to be affected by a rapid glucose breakdown in the isolated tissue. Neither such low values depend on a degrading of the intraextracellular Na+ concentration gradient, since this gradient seems to remain unchanged throughout the same time. In another group of experiments, in which phloretin was added to the perfusing blood (mean 0.6 X 10(-3) mol.l-1) at different glucose levels, the mean values of Gi/Ge in the cortical tissue were higher (in many cases greater than 1) than those obtained in a group of control kidneys perfused in absence of phloretin. According to the presented data, the mean Gi and Gi/Ge values, as calculated by us, seem to correspond to those existing in the functioning tissue just before its excision. The already suggested view that the low values of Gi and Gi/Ge could depend on the possible existence of a mechanism actively extruding glucose from the basolateral membrane of tubular cells seems to be reinforced.