The Nephropathy of Experimental Potassium Deficiency. An Electron Microscopic Study

Abstract

The most prominent abnormality in renal function in potassium depletion in man and in experimental animals is a defect in concentrating power. Although it has been suggested that in rats this may be due to lesions in the collecting tubules, the virtual absence of these histological abnormalities in human material and in dogs is paradoxical. In the experiments reported here, mild potassium depletion has been induced in rats by dietary restriction and the kidneys of these animals examined by the electron microscope. The most obvious early and constant abnormality was found in the basement membrane of the thin segment of the loop of Henle. The width of this membrane is increased to 3–5 times normal and it becomes fibrillar in appearance. This thickening and fibrillation involves also the pars recta of the proximal tubule, but does not extend into the thick ascending segment of the loop of Henle, the convoluted tubules or the collecting tubules. In the later stages of potassium depletion electron microscopy confirmed the abnormalities already reported in light microscopic studies— i.e. granulation, hyperplasia and degeneration of the cells of the collecting tubules. The relationship between the basement membrane abnormality and the known effect of potassium depletion on renal concentrating power is discussed in the light of the counter‐current hypothesis. It is suggested that the physical state of the ground substance of the basement membrane may have an important influence on the movement of water and electrolytes within the medullary region of the kidney and may be responsible for the renal defect in water conservation which occurs in potassium depletion.

The Electron Microscopic Appearance of the Kidney in Hydrated and Dehydrated Rats

“…While firm conclusions cannot be drawn regarding the functional significance of these changes, the alteration in tubular basement membrane which can be induced by hydration is almost certainly associated with changes in permeability which are likely to effect the counter-current mechanism. Similar but less marked changes in the basement membrane of some of the thin segments of the loop of Henle have recently been reported in rats undergoing saline diuresis and in potassium-depleted animals [Lapp and Nolte, 1962;MacDonald et al, 1962]. Electron microscopy of medulla from dehydrated animals did not reveal any structures in the collecting ducts corresponding to the "pores" described by Ginetsinsky.…”

Immunohistochemical localization of atrial natriuretic peptide in the developing and adult mammalian kidney

“…ANP has been shown to induce significant kaliuresis along with natriuresis (DeBold et al, 1981;Seymour et al, 1985). This effect may involve intercalated cells because several studies have demonstrated hypertrophy and increased numbers of intercalated cells in the outer medullary collecting ducts of hypokalemic or waterdeprived rats (Oliver et al, 1957;MacDonald et al, 1962;Hancox and Komender, 1963;Kennedy and Parker, 1963). The hypertrophic response included a transfer of membrane from apical vesicles to the luminal surface ofthe cell (Stetson et al, 1980;Brown et al, 1987) and was correlated with decreased urine-concentrating ability in K + -deficient animals.…”

A Correlated Study of Kidney Function and Ultrastructure in Potassium-Depleted Rats

“…A significant proportion of them, how ever, tended to sequester cytoplasmic components and appeared to be cytosegrosomes [27], One of the conspicuous constituents of these cytosegrosomes were ribosome-like particles. We could not ascertain whether some of the droplets were of mitochondrial origin [28], However, an elaborate membrane system was the sole constituent of several droplets. Many droplets appeared to be in the process of enlargement not only by fusing with each other, but also by incorporating cytoplasmic material through a gap in the discontinuous limiting membrane.…”