Selected aspects of cell volume control in renal cortical and medullary tissue

Abstract

Under normal physiological conditions, demands placed on mammalian renal cortical cells are quite different from those in the medulla. Cortical proximal tubule cells exist in an isotonic environment, but must resorb vast amounts of filtered fluid and solute, and also adjust to solute generated from cellular metabolism. In addition, cortical cells must also adjust to occasional pathological derangements in blood osmolality. By contrast, human medullary cells have a smaller solute resorptive load, but exist in a milieu where osmolality varies from 40 to more than 1200 mosmol/kg H2O, depending on water intake. Remarkably, the cells maintain a near normal size despite these stresses. Under isosmotic conditions, the primary regulator of cell volume is Na-K ATPase. In its absence, factors such as external protein, extracellular matrix and basement membrane, cytoskeleton, and perhaps formation of cytoplasmic vesicular-like structures help prevent cells from swelling massively. Under anisosmotic conditions, a variety of transport processes operating across basolateral and apical membranes either remove solute from or add solute (and water) to cells to minimize changes in their size. Medullary cells have the additional ability to accumulate organic, non-toxic, osmolytes that offset external hypertonicity and allow cells to maintain normal size without increasing cellular inorganic ion concentrations.

Tonicity-independent regulation of the osmosensitive transcription factor TonEBP (NFAT5)

“…It is without question that hypertonic stress plays a definitive role in the normal biological functions of the kidney, as daily NaCl osmolality levels can easily reach 1,000 -1,200 mosmol/kg in the kidney medulla during antidiuresis (38,74). Other slightly hypertonic tissues have been identified, such as the thymus, spleen, and liver (roughly 330 -335 mosmol/kg compared with blood osmolality at 300 mosmol/kg) (18).…”

Ultrasonographic findings in the kidney and urinary tract in children with vesicoureteral reflux

“…Smellie, reconoció la importancia patológica del reflujo y sugirió la posibilidad de que fuera uno de los mecanismos que permitan que la infección alcance el riñón (12) . Existe una amplia correlación entre el grado de reflujo y la cicatriz renal, a reflujo más severo mayor riesgo de cicatriz, lo que se observa en nuestro estudio; no obstante, Smellie y otros, hallaron que el 30% de los riñones en que aparecían nuevas cicatrices el reflujo era mínimo o estaba ausente (32,37) .…”

“…En ocasiones hay RVU severo sin cicatriz (3,6,32,37) . Se considera que los riñones con RVU de alto grado tiene un riesgo de hasta 3 veces superior de desarrollar cicatrices renales que los que tiene un RVU leve, porque en ellos la posibilidad de reflujo intrarrenal es mayor, así como los episodios de infección del tracto urinario recurrente (6) .…”

6. Fluid and Electrolytes (Na, Cl and K)

“…Total body water is divided into two compartments: intracellular fluid (ICF) and extracellular fluid (ECF). Potassium (K+) is the major ion of the ICF, and its intracellular concentration depends on the Na/K‐ATPase activity which is impaired at insufficient supplies of oxygen and energy (7). Premature infants are vulnerable to imbalances between intra‐ and extracellular compartments.…”