Total body potassium in normal children

Transient early-childhood hyperkalaemia without salt wasting, pathophysiological approach of three cases

Two types of early childhood hyperkalemia had been recognized, according to the presence or absence of urinary salt wasting. This condition was attributed to a maturation disorder of aldosterone receptors and is characterized by sustained hyperkalemia, hyperchloremic metabolic acidosis (MA) due to reduced ammonium urinary excretion and bicarbonate loss, and normal creatinine with growth delay. We present 3 patients of the type without salt wasting, which we will call transient early-childhood hyperkalemia (TECHH) without salt wasting, and discuss its physiopathology according to new insights into sodium and potassium handling by the aldosterone in distal nephron. In 3 children from 30 to 120-day-old admitted with bronchiolitis and growth delay hyperkalemia was found in routine laboratory. Further studies revealed a normal creatinine with inappropriately normal or low fractional excretion (FE) of potassium, accompanied by inadequately normal serum aldosterone and plasma renin activity for their higher plasma potassium levels, but without urine salt wasting. They also presented hyperchloremic MA with FE of bicarbonate 0.58%-2.2%, positive urinary anion gap during MA and normal ability to acidify the urine. Based on these findings a diagnosis of TECHH without salt wasting was made and they were treated sodium bicarbonate and hydrochlorothiazide with favorable response. The condition was transient in all cases leading to treatment discontinuation. Given that TECCH without salt wasting is a tubular disorder of transient nature with mild symptoms; it must be keep in mind in the differential diagnosis of hyperkalemia in young children.

Transient early-childhood hyperkalemia without salt wasting, physiopathological approach of three cases

Two types of early-childhood hyperkalemia had been recognized, according to the presence or absence of urinary salt wasting. This condition was attributed to a maturation disorder of aldosterone receptors and is characterized by sustained hyperkalemia, hyperchloremic metabolic acidosis due to reduced ammonium urinary excretion and bicarbonate loss, and normal creatinine with growth delay. We present three patients of the type without salt wasting, which we will call transient early-childhood hyperkalemia without salt wasting, and discuss its physiopathology according to new insights into sodium and potassium handling by the aldosterone in distal nephron. In three children from 30 to 120-day-old admitted with bronchiolitis and growth delay hyperkalemia was found in routine laboratory. Further studies revealed a normal creatinine with inappropriately normal or low fractional excretion of potassium, accompanied by inadequately normal serum aldosterone and plasma renin activity for their higher plasma potassium levels, but without urine salt wasting. They also presented hyperchloremic metabolic acidosis with fractional excretion of bicarbonate 0.58-2.2%, positive urinary anion gap during metabolic acidosis and normal ability to acidify the urine. Based on these findings a diagnosis of transient early-childhood hyperkalemia without salt wasting was made and they were treated sodium bicarbonate and hydrochlorothiazide with favorable response. The condition was transient in all cases leading to treatment discontinuation. Given that transient early-childhood hyperkalemia without salt wasting is a tubular disorder of transient nature with mild symptoms; it must be keep in mind in the differential diagnosis of hyperkalemia in young children.

An unexpected journey: conceptual evolution of mechanoregulated potassium transport in the distal nephron

Flow-induced K secretion (FIKS) in the aldosterone-sensitive distal nephron (ASDN) is mediated by large-conductance, Ca(2+)/stretch-activated BK channels composed of pore-forming α-subunits (BKα) and accessory β-subunits. This channel also plays a critical role in the renal adaptation to dietary K loading. Within the ASDN, the cortical collecting duct (CCD) is a major site for the final renal regulation of K homeostasis. Principal cells in the ASDN possess a single apical cilium whereas the surfaces of adjacent intercalated cells, devoid of cilia, are decorated with abundant microvilli and microplicae. Increases in tubular (urinary) flow rate, induced by volume expansion, diuretics, or a high K diet, subject CCD cells to hydrodynamic forces (fluid shear stress, circumferential stretch, and drag/torque on apical cilia and presumably microvilli/microplicae) that are transduced into increases in principal (PC) and intercalated (IC) cell cytoplasmic Ca(2+) concentration that activate apical voltage-, stretch- and Ca(2+)-activated BK channels, which mediate FIKS. This review summarizes studies by ourselves and others that have led to the evolving picture that the BK channel is localized in a macromolecular complex at the apical membrane, composed of mechanosensitive apical Ca(2+) channels and a variety of kinases/phosphatases as well as other signaling molecules anchored to the cytoskeleton, and that an increase in tubular fluid flow rate leads to IC- and PC-specific responses determined, in large part, by the cell-specific composition of the BK channels.

Potassium transport in the maturing kidney

The distal nephron and colon are the primary sites of regulation of potassium (K(+)) homeostasis, responsible for maintaining a zero balance in adults and net positive balance in growing infants and children. Distal nephron segments can either secrete or reabsorb K(+) depending on the metabolic needs of the organism. In the healthy adult kidney, K(+) secretion predominates over K(+) absorption. Baseline K(+) secretion occurs via the apical low-conductance secretory K(+) (SK) channel, whereas the maxi-K channel mediates flow-stimulated net urinary K(+) secretion. The K(+) retention characteristic of the neonatal kidney appears to be due not only to the absence of apical secretory K(+) channels in the distal nephron but also to a predominance of apical H-K-adenosine triphosphatase (ATPase), which presumably mediates K(+) absorption. Both luminal and peritubular factors regulate the balance between K(+) secretion and absorption. Perturbation in any of these factors can lead to K(+) imbalance. In turn, these factors may serve as effective targets for the treatment of both hyper-and hypokalemia. The purpose of this review is to present an overview of recent advances in our understanding of mechanisms of K(+) transport in the maturing kidney.

Molecular regulation and physiology of the H+,K+ -ATPases in kidney

Two H(+), K(+)-adenosine triphosphatase (ATPase) proteins participate in K(+) absorption and H(+) secretion in the renal medulla. Both the gastric (HKalpha(1)) and colonic (HKalpha(2)) H(+),K(+)-ATPases have been localized and characterized by a number of techniques, and are known to be highly regulated in response to acid-base and electrolyte disturbances. Both ATPases are dimers of composition alpha/beta that localize to the apical membrane and both interact with the tetraspanin protein CD63. Although CD63 interacts with the carboxy-terminus of the alpha-subunit of the colonic H(+),K(+)-ATPase, it interacts with the beta-subunit of the gastric H(+),K(+)-ATPase. Pharmacologically, both ATPases are distinct; for example, the gastric H(+),K(+)-ATPase is inhibited by Sch-28080, but the colonic H(+),K(+)-ATPase is inhibited by ouabain (a classic inhibitor of the Na(+)-pump) and is completely insensitive to Sch-28080. The alpha-subunit of the colonic H(+),K(+)-ATPase is the only subunit of the X(+),K(+)-ATPase superfamily that has 3 different splice variants that emerge by deletion or elongation of the amino-terminus. The messenger RNA and protein of one of these splice variants (HKalpha(2C)) is specifically up-regulated in newborn rats and becomes undetectable in adult rats. Therefore, HKalpha(2), in addition to its role in potassium and acid-base homeostasis, appears to play a significant role in early growth and development. Finally, because chronic hypokalemia appears to be the most potent stimulus for upregulation of HKalpha(2), we propose that the HKalpha(2) participates importantly in the maintenance of chronic metabolic alkalosis.

Renal potassium handling in healthy and sick newborns

Growing infants must maintain a state of positive K+ balance, a task accomplished, in large part, by the kidney. The distal nephron is uniquely adapted to retain total body K+ early in life. The magnitude and direction of net K+ transport in the cortical collecting duct (CCD), the segment responsible for the final renal regulation of K+ balance in the adult, reflect the balance of opposing fluxes of K+ secretion and K+ absorption. Evidence now indicates that the low capacity of the neonatal CCD for K+ secretion is due, at least in part, to a relative paucity of conducting K+ channels in the urinary membrane. A relative excess of K+ absorption in this nephron segment may further reduce net urinary K+ secretion. Under conditions prevailing in vivo, the balance of fluxes in the CCD likely contributes to the relative K+ retention characteristic of the neonatal kidney.

Body compartment changes in sick children

Our studies showed that there are important changes in body composition in children in response to dieting and refeeding. Similarly, we showed changes in body composition in response to renal transplantation, which would be expected to restore more normal homeostasis, but in its early phases changes in body composition are complicated by the use of high doses of drugs, notably steroid. Some of the changes in body composition can be predicted from changes in weight but the majority cannot. Relatively simple measurements like the four skinfolds as a means of determining body fat are surprisingly accurate, except in extremely obese subjects. Similarly, the measurements of fat free body mass are useful. However, this measurement does not discriminate changes within fat free body mass in the proportions of body cell mass versus extracellular mass. Similarly, none of these measurements provide any information regarding the composition of body cell mass with regard to its potassium and protein content (as reflected by total body nitrogen). The main drawback with total body nitrogen measurements is the radiation exposure. Thus, we have had to limit the inclusion of total body nitrogen measurements. It has been estimated that two total body nitrogen measurements provide a gonadal dose of radiation roughly equivalent to that experienced by an individual living in a large North American city, that means 30 to 50 mREM per each total body nitrogen measurement. It becomes ethically possible then to carry out nitrogen measurements where it can be argued that their measurement is essential in monitoring the safety and well being of the subject; or alternatively if the subject's life expectancy is limited.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of anthropometric dimensions to lean body mass in children

This study is designed to compare the predictability of lean body mass, as measured by whole-body 40K spectrometry, from skinfolds, circumferences and skeletal widths in children 7 to 12 years of age. The specific skinfold sites were back, upper arm, side, waist, abdomen, and calf; the circumference sites were forearm, upper arm (flexed), wrist, thigh, calf, and chest (deflated); skeletal widths included wrist, knee, ankle, elbow, shoulder and hip. In a group of 163 boys, three skinfolds and body weight accounted for 89.7% of the variation in LBM, two circumferences and height and weight accounted for 87.2% of the variation in LBM, and two skeletal widths and height and weight accounted for 87.4% of the variation in LBM. Combining all measurement variables into one analysis resulted in five significant variables: weight, side skinfold, abdomen skinfold, forearm circumference and chest circumference with the coefficient of determination 90.6%, only slightly higher than with weight and three skinfolds. The significant variables from the combined analysis were then used to predict LBM in five separate age groups of boys and a sample of 44 girls. In general, weight, forearm and chest circumference contributed positively to LBM and side and abdomen skinfolds contributed negatively. The regression coefficients for each site were not significantly different among age groups. LBM in children can be estimated from skinfolds, circumferences or skeletal widths with considerable success, as has been shown to be the case in college-age adults.