TRANSPORT CHARACTERISTICS IN SPECIFIC RENAL CELL TYPES

I propose to study the molecular mechanisms of transport of organic
substrates in specific renal cell types. Na-dependent transport systems in
proximal tubular cells represent the dominant pathways for reabsorption in
the kidney, yet the mechanism(s) for this type of 'coupled'-transport
remains to be elucidated for any class of substrates. Such information is
necessary to understand basic questions concerning the movement of
molecules across cell membranes. The proposed approach involves measuring
transport in three systems: intact, isolated cells, ATP-depleted cell
'models', and apical (brush border) membrane vesicles. Each system offers
unique advantages in characterizing transport in the kidney. In particular
I propose to study the transport of four different subtrates: D-glucose,
L-lactate, L-proline, and succinate. Each is a model substrate for a
separate Na-dependent pathway, and each represents an important class of
compounds in renal metabolism. I will examine the effect of membrane
potential and ionic composition on the kinetics of transport of these
compounds, and determine the effects on transport of various classes of
inhibitors. Basal-lateral transport processes will be examined by
comparing transport of each substrate in both brush border membrane
vesicles and in intact, isolated cells under similar expermental
conditions. The data gained from these studies will be used to develop
models describing the qualitative and quantitative characteristics of
transport of each class of test substrates. Long term goals include the
preparation of purified distal tubular cells and the separation of proximal
cells into enriched populations of S1 and S2 cells. These procedures will
permit the characterization of transport processes in each cell type, and
will provide systems for biochemical and tissue culture studies.