In vivo PTH provokes apical NHE3 and NaPi2 redistribution and Na-K-ATPase inhibition.

The aim of this study was to test the hypothesis that in vivo administration of parathyroid hormone (PTH) provokes diuresis/natriuresis through redistribution of proximal tubule apical sodium cotransporters (NHE3 and NaPi2) to internal stores and inhibition of basolateral Na-K-ATPase activity and to determine whether the same cellular signals drive the changes in apical and basolateral transporters. PTH-(1-34) (20 U), which couples to adenylate cyclase (AC), phospholipase C (PLC), and phospholipase A2 (PLA2), or [Nle8,18,Tyr34]PTH-(3-34) (10 U), which couples to PLC and PLA2 but not AC, were given to anesthetized rats as an intravenous bolus followed by low-dose infusion (1 U. kg-1. min-1 for 1 h). Renal cortex membranes were fractionated on sorbitol density gradients. PTH-(1-34) increased urinary cAMP excretion 3-fold, urine output (V) 2.0 +/- 0.1-fold, and lithium clearance (CLi) 2.8 +/- 0.3-fold. With this diuresis/natriuresis, 25% of NHE3 and 18% of NaPi2 immunoreactivity redistributed from apical membranes to higher density fractions containing intracellular membrane markers, and basolateral Na-K-ATPase activity decreased 25%. [Nle8,18,Tyr34]PTH-(3-34) failed to increase V or CLi or to provoke redistribution of NHE3 or NaPi2, but it did inhibit Na-K-ATPase activity 25%. We conclude that in vivo PTH stimulates natriuresis/diuresis associated with internalization of apical NHE3 and NaPi2 and inhibition of Na-K-ATPase activity, that cAMP-protein kinase A stimulation is necessary for the natriuresis/diuresis and NHE3 and NaPi2 internalization, and that Na-K-ATPase inhibition is not secondary to depressed apical Na+ transport.

Reversible effects of acute hypertension on proximal tubule sodium transporters.

Acute hypertension provokes a rapid decrease in proximal tubule sodium reabsorption with a decrease in basolateral membrane sodium-potassium-ATPase activity and an increase in the density of membranes containing apical membrane sodium/hydrogen exchangers (NHE3) [Y. Zhang, A. K. Mircheff, C. B. Hensley, C. E. Magyar, D. G. Warnock, R. Chambrey, K.-P. Yip, D. J. Marsh, N.-H. Holstein-Rathlou, and A. A. McDonough. Am. J. Physiol. 270 (Renal Fluid Electrolyte Physiol. 39): F1004-F1014, 1996]. To determine the reversibility and specificity of these responses, rats were subjected to 1) elevation of blood pressure (BP) of 50 mmHg for 5 min, 2) restoration of normotension after the first protocol, or 3) sham operation. Systolic hypertension increased urine output and endogenous lithium clearance three- to fivefold within 5 min, but these returned to basal levels only 15 min after BP was restored. Renal cortex lysate was fractionated on sorbitol gradients. Basolateral membrane sodium-potassium-ATPase activity (but not subunit immunoreactivity) decreased one-third to one-half after BP was elevated and recovered after BP was normalized. After BP was elevated, 55% of the apical NHE3 immunoreactivity, smaller fractions of sodium-phosphate cotransporter immunoreactivity, and apical alkaline phosphatase and dipeptidyl-peptidase redistributed to membranes of higher density enriched in markers of the intermicrovillar cleft (megalin) and endosomes (Rab 4 and Rab 5), whereas density distributions of the apical cytoskeleton protein villin were unaltered. After 20 min of normalized BP, all the NHE3 and smaller fractions of the other apical membrane proteins returned to their original distributions. These findings suggest that the dynamic regulation of proximal tubule sodium transport by acute changes in BP may be mediated by rapid reversible regulation of sodium pump activity and relocation of apical sodium transporters.

Na-K-ATPase in lacrimal gland acinar cell endosomal system: correcting a case of mistaken identity.

Na-K-ATPase is associated with a variety of membrane populations in lacrimal acinar cells. Acinus-like structures formed by rabbit acinar cells in primary culture were incubated with horseradish peroxidase (HRP) to label basolateral and endosomal membranes and then analyzed by electron microscopy cytochemistry with the 3-3'-diaminobenzidine reaction or by fractionation and measurement of marker catalytic activities or immunoreactivities. HRP adsorbed to basolateral membranes at 4 degrees C. Fractionation showed it associated with low-density membranes enriched in acid phosphatase and TGN38 but containing only minor amounts of Na-K-ATPase. Cells internalized HRP to cytoplasmic vesicles, Golgi structures, and lysosomes at 37 degrees C. The major endosomal compartment revealed by fractionation coincided with major peaks of Na-K-ATPase and Rab6 and secondary peaks of galactosyltransferase and gamma-adaptin. Carbachol (10 microM) increased lysosomal and Golgi labeling. Thus most of the Na-K-ATPase is located in the basolateral membrane-oriented endosomal system, concentrated in a compartment possibly related to the trans-Golgi network. Constitutive and stimulation-accelerated traffic to and from this compartment may serve several exocrine cell functions.

Evaluation of a pneumonia practice guideline in an interventional trial.

There are few available data to define the medically necessary duration of stay for patients hospitalized with pneumonia. Therefore, we investigated the safety and effectiveness of a practice guideline that provided information about switching patients from parenteral to oral antimicrobials and early hospital discharge. The study was a prospective controlled study with an alternate month design. The practice guideline was studied in 146 "low-risk" pneumonia patients hospitalized during a 22-month period. Medical care consistent with the practice guideline occurred in 64% and 76% of patients during control and intervention periods, respectively (p=0.15). There were no differences in patient outcomes in the control and intervention groups when measured 1 mo after hospital discharge, including hospital readmission rates, health-related quality of life, and patient satisfaction. Explicit and implicit review revealed that 98.6% (95% confidence interval [CI]: 95.1%, 99.8%) of low-risk patients would not have benefited from continued hospitalization after the fourth hospital day. The 30-d survival rate of the low-risk pneumonia patients was 99.3% (95% CI: 96.2%, 100%) and patient outcomes appeared to be favorable compared with previously published values. We conclude that duration of hospital stay was frequently consistent with the practice guideline in both study groups, and patient outcomes remained unchanged. The guideline will require additional testing before it can be recommended for use.