2--7--bis(carboxyethyl)-5(6)-carboxyfluorescein and Acute-Disease

We previously showed that acute arterial hypertension induces an inhibition of fluid and NaCl reabsorption in proximal tubules of Sprague-Dawley rats, which is associated with a rapid reversible internalization of apical Na(+)/H(+) exchanger in brush border. To determine whether there is a corresponding inhibition of apical Na(+)/H(+) exchanger activity in proximal tubules to account for the reduced tubular reabsorption, an instrument capable of measuring intracellular pH (pH(i)) ratiometrically and repeatedly on the surface of kidney with high temporal resolution is required. We report the design and validation of such a fluorimetric system based on two ultraviolet nitrogen-pulsed lasers and a photomultiplier. pH(i) of proximal tubules in situ was measured with pH-sensitive fluorescence dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein at 5 Hz. Using the initial rate of change of pH(i) (dpH(i)/dt) during luminal Na(+) removal as an index of apical Na(+)/H(+) exchanger activity, the exchanger activity was found to be reduced by 52 +/- 11% (n = 14, P < 0.05) compared with the baseline after 20 min of induced acute hypertension. The inhibition of Na(+)/H(+) exchange activity was alleviated when the blood pressure was returned to prehypertensive level. These observations indicate that acute changes in arterial pressure can reversibly inhibit apical Na(+)/H(+) exchanger activity, which might contribute to pressure natriuresis in proximal tubule.

Topics: Acute Disease; Ammonium Chloride; Animals; Fluoresceins; Fluorescent Dyes; Hydrogen-Ion Concentration; Hypertension; Kidney Tubules, Proximal; Kinetics; Male; Microvilli; Rats; Rats, Sprague-Dawley; Sodium-Hydrogen Exchangers; Software

Magnesium deficiency (MgD) has been associated with production of reactive oxygen species, cytokines, and eicosanoids, as well as vascular compromise in vivo. Although MgD-induced inflammatory change occurs during "chronic" MgD in vivo, acute MgD may also affect the vasculature and consequently, predispose endothelial cells (EC) to perturbations associated with chronic MgD. As oxyradical production is a significant component of chronic MgD, we examined the effect of acute MgD on EC oxidant production in vitro. In addition we determined EC; pH, mitochondrial function, lysosomal integrity and general cellular antioxidant capacity. Decreasing Mg2+ (< or = 250microM) significantlyincreased EC oxidant production relative to control Mg2+ (1000microM). MgD-induced oxidant production, occurring within 30min, was attenuated by EC treatment with oxyradical scavengers and inhibitors of eicosanoid biosynthesis. Coincident with increased oxidant production were reductions in intracellular glutathione (GSH) and corresponding EC alkalinization. These data suggest that acute MgD is sufficient for induction of EC oxidant production, the extent of which may determine, at least in part, the extent of EC dysfunction/injury associated with chronic MgD.

Topics: Acute Disease; Animals; Aorta; Catalase; Cattle; Cell Survival; Cells, Cultured; Coloring Agents; Eicosanoids; Endothelium, Vascular; Fluoresceins; Fluorescence; Fluorescent Dyes; Glutathione; Hydrogen-Ion Concentration; Lysosomes; Magnesium Deficiency; Mitochondria; Neutral Red; Oxidation-Reduction; Reactive Oxygen Species; Rhodamine 123; Rhodamines; Superoxide Dismutase

The effect of acid-base disturbances on sodium/proton (Na+/H+) exchange has been examined in animal models; however, few data are available from human studies. To test the effect of metabolic acidosis on Na+/H+ exchange in man, as well as to examine the relationship between Na+/H+ exchange and cytosolic calcium ([Ca2+]i), we measured both variables in patients with decreased renal function with mild metabolic acidosis (pH 7.34 +/- 0.06), in normal control subjects (pH 7.41 +/- 0.02), and in subjects before (pH 7.40 +/- 0.01), and after (pH 7.26 +/- 0.04) ammonium chloride (NH4Cl) 15 g for 5 d. Lymphocytes and platelets were loaded with the cytosolic pH (pHi) indicator 2'-7'-bis(carboxyethyl)-5,6-carboxyfluorescein and acidified to pH approximately 6.6 with propionic acid. To quantitate Na+/H+ exchange, dpHi/dt was determined at 1 min. [Ca2+]i was measured with fura-2. Na+/H+ exchange was significantly increased only in lymphocytes of patients with renal insufficiency. Neither intracellular pH (pHi) nor [Ca2+]i was different from controls. NH4Cl resulted in a significant increase in Na+/H+ exchange in lymphocytes, but not in platelets of normal subjects. Values of pHi and [Ca2+]i in either cell type remained unaffected. Since metabolic acidosis influenced Na+/H+ only in lymphocytes, but not in platelets, it is possible that protein synthesis may be involved in increasing Na+/H+ exchange.

Topics: Acidosis; Acidosis, Renal Tubular; Acute Disease; Blood Platelets; Carbon Dioxide; Carrier Proteins; Chronic Disease; Electrolytes; Fluoresceins; Fluorescent Dyes; Humans; Hydrogen-Ion Concentration; In Vitro Techniques; Kinetics; Lymphocytes; Male; Sodium; Sodium-Hydrogen Exchangers