The renal proximal tubule (original) (raw)

I. INTRODUCTION Methodologic as well as conceptual progress during the past decade has made it possible for renal physiologists to "peek" inside the epithelial. 'black box" of renal tubular function with a greater degree of confidence than ever before. Among the more important developments have been: (I) evolution of the fluid mosaic model of plasma membrane structure (Singer and Nicolson, 1972), (2) emergence of a role for the cytoskeleton as a regulator of membrane function (Nicolson and Poste, 1976), (3) maturation of the concept that electrochemical potential gradients can provide the driving force for transport systems, i.e., Na+ gradient, chemiosmotic hypotheses (Crane, 1977; Mitchell, 1976) without being coupled directly to metabolic intermediates, (4) application of sophisticated electrophysiologic measurements to the elucidation of renal transport processes at opposing membrane surfaces (Gottschalk and Lassiter, 1973), (5) ill I'itro perfusion of isolated tubule segments (Burg and Orloff, 1973), (6) biochemical separation of epithelial cellular organelles, especially isolation and separation of clean membrane fractions from luminal (brush border) and antiluminal (basolateral) membrane surfaces (Heidrich et al., 1972), and (7) ill vivo characterization of substrate interactions with luminal as distinct from antiluminal nephron surfaces (Silverman et al., 1971kl,b).