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Tubular organization and vascular-tubular relations were studied by double injection in canine kidneys. Blood vessels were injected via the artery after perfusion fixation. Tubules were injected by micropipettes inserted into the urinary spaces of selected glomeruli in cleared slices. One hundred proximal convoluted tubules, 16 Henle loops, and 5 distal convoluted tubules were defined. Only subcapsular proximal convolutions were perfused by efferent vessels arising from the same glomerulus (43 of 55). In midcortex, proximal convolutions were generally perfused over less than half their length by the parent efferent (21 of 31). Here tubules entirely perfused by the parent efferent were rare (2 of 31). No inner cortical proximal convolutions were perfused by the efferent from the same glomerulus (0 of 14). Henle's loops were found to be perfused by the efferents of many glomeruli regardless of the cortical position of the parent glomerulus. Distal convolutions shared the perfusion of proximal convolutions of the same glomerulus. Thus, each nephron is apparently functionally dependent on efferent blood from glomeruli of many other nephrons. New synoptic diagrams of canine renal organization are presented.

The electrolyte and water content of cellular and interstitial compartments in the renal papilla of the rat was determined by x-ray microanalysis of frozen-hydrated tissue sections . Papillae from rats on ad libitum water were rapidly frozen in a slush of Freon 12, and sectioned in a cryomicrotome at -30 to -40°C . Frozen 0.5-,um sections were mounted on carbon-coated nylon film over a Be grid, transferred cold to the scanning microscope, and maintained at -175°C during analysis . The scanning transmission mode was used for imaging. Structural preservation was of good quality and allowed identification of tissue compartments . Tissue mass (solutes + water) was determined by continuum radiation from regions of interest . After drying in the SEM, elemental composition of morphologically defined compartments (solutes) was determined by analysis of specific x-rays, and total dry mass by continuum. Na, K, CI, and H2O contents in collecting-duct cells (CDC), papillary epithelial cells (PEC), and interstitial cells (IC) and space were measured . Cells had lower water content (mean 58 .7%) than interstitium (77.5%) . Intracellular K concentrations (millimoles per kilogram wet weight) were unremarkable (79-156 mm/kg wet weight) ; P was markedly higher in cells than in interstitium . S was the same in all compartments . Intracellular Na levels were extremely high (CDC, 344 ± 127 SD mm/kg wet weight ; PEC, 287 ± 105; IC, 898 ± 194) . Mean interstitial Na was 590 ± 119 mm/Kg wet weight . CI values paralleled those for Na . If this Na is unbound, then these data suggest that renal papillary interstitial cells adapt to their hyperosmotic environment by a Na-uptake process.Cells of the rat renal papilla are exposed to wide changes in the ionic and osmotic composition of their environment . The papillary epithelium of the rat is exposed to urine whose osmolality ranges from <100 to >3,000 mosmol/kg H2O. Tubular and interstitial cells within the papilla live in the hypertonic environment associated with the urine-concentrating mechanism. Because few mammalian cell types are exposed to such environmental conditions, the mechanism by which these cells adapt to the high salt and urea content of their environment is of great interest to cell biologists. and Morgan (20), using in vitro centrifugation or incubation techniques, have reported that the Na content of papillary cells increases with increasing osmolality and reaches more than 400 mM. However, until recently no method existed for the 274 definition of chemical composition of defined cell types within the papilla. The development of techniques for direct x-ray microanalysis of frozen-hydrated tissue sections (19,22,23) now makes such analysis possible. MATERIALS AND METHODSSix male Long-Evans rats (bred in our colony), weighing 125-200 g, were housed individually in metabolic cages for 2 dor more before the experiment . They were given Purina Rat Chow (0.29% Na, 0.46% K; Ralston Purina Co., St. Louis, Mo.) and water ad libitum. An overnight urine sample was collecte...

X-ray microanalysis of frozen-hydrated tissue sections permits direct quantitative analysis of diffusible elements in defined cellular compartments . Because the sections are hydrated, elemental concentrations can be defined as wet-weight mass fractions . Use of these techniques should also permit determination of water fraction in cellular compartments . Reliable preparative techniques provide flat, smooth, 0.5 p,m-thick sections with little elemental and morphological disruption . The specimen support and transfer system described permits hydrated sections to be transferred to the scanning electron microscope cold stage for examination and analysis without contamination or water loss and without introduction of extraneous x-ray radiation .X-ray microanalysis of frozen-hydrated tissue sections is potentially an ideal method for analyzing diffusible elements in tissues. This paper describes a practical method of specimen handling for quantitative x-ray analysis of fully frozen-hydrated tissue sections in scanning electron microscopes (SEM) fitted with energy dispersive x-ray detectors. The success of the method is based on advances in two areas. First, reliable preparative techniques were developed to provide flat, smooth, 0 .5-Lm-thick sections with little elemental redistribution and morphologic disruption . Second, a specimen support and transfersystem was developed that allowed sections to be transferred to the SEM cold stage for examination and analysis without contamination or loss of water and without introducing extraneous x-ray radiation sources. The cryochamber (Fig . 1) was constructed of foam polystyrene sheets (2.5 cm thick), and attached to the microtome knife stage so that chamber and knife moved together in the horizontal plane. The chamber was cooled by a continuous flow of dry Ns gas at constant low temperature, which entered the chamber beneath a secondary floor 10 mm above the main chamber floor . The cold Nz gas was produced by boiling Liquid nitrogen (LN2) in a pressurized 25-Liter Dewar flask with an electrical immersion heater . Heat input, and hence gas flow rate, was adjusted by an autotransformer. Gas leaving the Dewar flask was reheated to the desired temperature by passing through an insulated resistor (Ohmite, 100 S2,225 W, #0904) connected to a separate autotransformer. Specimen temperature was estimated by using a thermistor mounted on the chuck assembly . All "cutting temperatures" were measured at this point .Sections were cut with a single-edge razor blade (Plus Platinum; Schick, Inc ., Westport, Conn.), mounted in a brass vise, which clamped the razor blade with 2-3 mm of the edge extended, and which incorporated an antiroll device consisting of a microscope slide held (in a movable mounting) with its edge parallel to the upper surface of the blade (Fig . 2) . The angle and spacing of the antiroll plate was set before cooling the chamber and final adjustment was made just before sectioning. All sections were cut with the microtome advance set for 0.5-lm section thickn...