Function of distal convoluted and connecting tubules studied by isolated nephron fragments

Abstract

Functions of the DCT (distal convoluted tubule) and the CNT (connecting tubule) were reviewed briefly with respect to anatomical, biochemical, and physiological aspects. Anatomical and biochemical aspects are mentioned briefly to provide information relevant to understanding the physiological aspects. It is clear that the DCT and the CNT, at least in rabbit kidneys, are distinct segments with respect to these three features. The functional distinctions are especially evident when hormonal responses are considered. The DCT is responsive to calcitonin, whereas the CNT responds to PTH, AVP, and isoproterenol. The multiplicity of the responses of the CNT may reflect the anatomical multiplicity. Although it is possible that different types of cells may be effecting different functions, definite evidence for such intrasegmental heterogeneity is still lacking. There are a few common characteristics between the DCT and the CNT. Both segments are impermeable to water and probably have high capacity for active sodium transport. The basolateral membrane of both segments may have a common physicochemical property allowing specific bindings of agents with membrane stabilizing action. The rabbit is thus far the only mammalian species in which we can examine the function of the DCT and CNT by the in vitro microperfusion technique. The possibility of interspecies differences must be taken into consideration before generalizing the findings from the rabbit nephron.