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The study of sugar metabolism in the kidney has been the subject of many previous investigations. Many attempts have been made to understand the nature of the carrier system(s) for sugar transport, to localize the transport site and also to study the possibility of the presence of a variety of pathways for sugar transport.
The kinetic data, the competitive inhibition studies and different degrees of sensitivity to inhibitor (e.g. Phlorizin) strongly suggest the presence of several pathways for sugar transport which may, or may not, be shared partly or completely by other sugars. These possibilities have been previously suggested by in vitro(A.Kleinzeller,197O A) and in vivo(23) (M.Silverman et al,1970’experiments.
Since the clearance experiments show the vector of transport in vivo, These experiments can be employed to study the 1:ransepithelial transport of sugars in kidney cells in vivo. In vivo studies can be undertaken to examine Tran epithelial transport and cellular accumulation simultaneously. To establish the pathway(s) involved in the transport of a sugar, one may combine the observations obtained from clearance experiments with those obtained from determination of tissue/plasma ratio in vivo. Assume that the sugar is found to be transported into the cell at the luminal face and is also accumulated in the cell, then an active transport at the luminal site can be established. This assumes that the site of reabsorption and accumulation is the same.
Employing clearance technique and T/P ratio determination is a good approach to study the mechanism(s) of sugar transport in vivo, that is to study the pathways involved in the transport, tie localization of pathways and their nature. It has been previously notice (A.Kleinzeller, 1970A) that there is a good correlation between the active accumulation of sugars in kidney slices (in vitro) and the reabsorption of sugar in vivo.
?- Methyl-D-glucoside, which has the known structural requirements for an active, Na+-dependent transport(l) is used in the present studies. This glucoside has been found to be accumulated very actively in kidney cortex slices in vitro. Both the ?S?i /?s? o value and it’s V max (65µ moles/g cell water per h) are high( A.Kleinzeller,l97OA) .No glucosidase activity is detected in the tissue; therefore, there will not be a ?S?i /?s? o decrease due to rapid intracellular metabolism.
Because of the above reasons ?MDG was chosen to start this series of experiments which is hoped to yield more information about the properties of the sugar transport system. The study of this glucoside can be followed by extensive studies on different other sugars including galactose ,glucose, and their 2- dioxy derivatives. Clearance of the sugars, their T/P ratio, competitive behavior, saturation and phlorizin. sensitivity can also be studied.