Atrial natriuretic peptide inhibits a cation channel in renal inner medullary collecting duct cells.

The patch-clamp technique was used to examine the effects of atrial natriuretic peptide (ANP) and its second messenger guanosine 3',5'-monophosphate (cGMP) on an amiloride-sensitive cation channel in the apical membrane of renal inner medullary collecting duct cells. Both ANP (10(-11) M) and dibutyryl guanosine 3',5'-monophosphate (10(-4) M) inhibited the channel in cell-attached patches, and cGMP (10(-5) M) inhibited the channel in inside-out patches. The inner medullary collecting duct is the first tissue in which ANP, via its second messenger cGMP, has been shown to regulate single ion channels. The results suggest that the natriuretic action of ANP is related in part to cGMP-mediated inhibition of electrogenic Na+ absorption by the inner medullary collecting duct.

Regulation by adrenal corticosteroids of sodium and potassium transport in loop of Henle and distal tubule of rat kidney.

Studies were conducted to examine the effects of adrenalectomy (ADX) and selective, physiological adrenal corticosteroid replacement on sodium and potassium transport by the superficial loop of Henle and distal tubule of rat kidney in vivo. In the loop of Henle, ADX inhibited sodium reabsorption by 33%. Whereas dexamethasone had no effect on reabsorption, aldosterone increased sodium transport to control levels. Thus, physiological levels of mineralocorticoids, but not glucocorticoids, control a fraction of sodium reabsorption in the loop of Henle. ADX also inhibited potassium reabsorption in the loop of Henle. Both dexamethasone and aldosterone reversed the inhibition, although only aldosterone increased reabsorption to control levels. In the distal tubule, ADX reduced sodium reabsorption by 44%. Both aldosterone and dexamethasone stimulated reabsorption: however, only aldosterone increased transport to control. Potassium secretion by the distal tubule was also reduced 34% by ADX. Aldosterone, but not dexamethasone, stimulated secretion. Thus, physiological levels of aldosterone regulate a fraction of sodium reabsorption and potassium secretion in the distal tubule.

Guanine nucleotide-binding protein, alpha i-3, directly activates a cation channel in rat renal inner medullary collecting duct cells.

We examined whether GTP binding proteins (G proteins) regulate sodium conducting channels in the apical membrane of renal inner medullary collecting duct (IMCD) cells and thereby modulate sodium absorption. Patch clamp studies were conducted on inside-out patches of the apical membrane of IMCD cells grown in primary culture. Guanosine 5'-triphosphate (GTP) and the nonhydrolyzable GTP analogue, GTP gamma S, which activate G proteins, increased the open probability of the cation channel. In contrast, the nonhydrolyzable GDP analogue, GDP beta S, which decreases G protein activity, inhibited the channel. Pertussis toxin also reduced the open probability of the channel. Addition of the alpha *i-3 subunit of Gi to the solution bathing the cytoplasmic surface of the membrane increased the open probability in a dose-dependent manner (2-200 pM). The threshold concentration for activation by alpha *i-3 was 2 pM. Activation of the cation channel by alpha *i-3 was not mediated via a protein kinase. The IMCD is the first polarized epithelium in which an ion channel has been shown to be directly regulated by a G protein. Thus, G proteins are important elements in regulating sodium absorption by the IMCD.

Differential acute effects of aldosterone, dexamethasone, and hyperkalemia on distal tubular potassium secretion in the rat kidney.

To determine the specific effects on renal potassium transport of acute elevations in plasma aldosterone, dexamethasone, and potassium concentrations, we studied adrenalectomized rats prepared such that each factor could be varied independently. Clearance data alone could not be used to deduce the underlying tubular transport effects, however, since infusion of each of these agents was associated with a marked change in urinary flow rate, which may itself have influenced potassium excretion. We therefore used a technique of continuous microperfusion, in vivo, of single superficial distal tubules to evaluate potassium secretion at constant luminal flow rate during each experimental maneuver. Acute aldosterone infusion was associated with a 90% stimulation of potassium secretion by microperfused tubules. However, total kidney sodium excretion and urinary flow rate were markedly reduced, and these factors opposed the direct tubular action of aldosterone, resulting in no net change in the amount of potassium excreted into the final urine. Conversely, dexamethasone had no direct effect on potassium secretion by single microperfused tubules, but it caused a sharp increase in urinary flow and sodium excretion, and secondarily enhanced urinary potassium excretion by 50%. Hyperkalemia per se stimulated renal potassium excretion both via a direct tubular effect and by increasing urinary flow rate. We conclude that urinary potassium excretion after infusion of each of these agents represents the net result of direct tubular effects and secondary flow-mediated changes.

Adenosine regulates a chloride channel via protein kinase C and a G protein in a rabbit cortical collecting duct cell line.

We examined the regulation by adenosine of a 305-pS chloride (Cl-) channel in the apical membrane of a continuous cell line derived from rabbit cortical collecting duct (RCCT-28A) using the patch clamp technique. Stimulation of A1 adenosine receptors by N6-cyclohexyladenosine (CHA) activated the channel in cell-attached patches. Phorbol 12,13-didecanoate and 1-oleoyl 2-acetylglycerol, activators of protein kinase C (PKC), mimicked the effect of CHA, whereas the PKC inhibitor H7 blocked the action of CHA. Stimulation of A1 adenosine receptors also increased the production of diacylglycerol, an activator of PKC. Exogenous PKC added to the cytoplasmic face of inside-out patches also stimulated the Cl- channel. Alkaline phosphatase reversed PKC activation. These results show that stimulation of A1 adenosine receptors activates a 305-pS Cl-channel in the apical membrane by a phosphorylation-dependent pathway involving PKC. In previous studies, we showed that the protein G alpha i-3 activated the 305-pS Cl- channel (Schwiebert et al. 1990. J. Biol. Chem. 265:7725-7728). We, therefore, tested the hypothesis that PKC activates the channel by a G protein-dependent pathway. In inside-out patches, pertussis toxin blocked PKC activation of the channel. In contrast, H7 did not prevent G protein activation of the channel. We conclude that adenosine activates a 305-pS Cl- channel in the apical membrane of RCCT-28A cells by a membrane-delimited pathway involving an A1 adenosine receptor, phospholipase C, diacylglycerol, PKC, and a G protein. Because we have shown, in previous studies, that this Cl- channel participates in the regulatory volume decrease subsequent to cell swelling, adenosine release during ischemic cell swelling may activate the Cl-channel and restore cell volume.

A PDZ-interacting domain in CFTR is an apical membrane polarization signal.

Polarization of the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated chloride channel, to the apical plasma membrane of epithelial cells is critical for vectorial transport of chloride in a variety of epithelia, including the airway, pancreas, intestine, and kidney. However, the motifs that localize CFTR to the apical membrane are unknown. We report that the last 3 amino acids in the COOH-terminus of CFTR (T-R-L) comprise a PDZ-interacting domain that is required for the polarization of CFTR to the apical plasma membrane in human airway and kidney epithelial cells. In addition, the CFTR mutant, S1455X, which lacks the 26 COOH-terminal amino acids, including the PDZ-interacting domain, is mispolarized to the lateral membrane. We also demonstrate that CFTR binds to ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50), an apical membrane PDZ domain-containing protein. We propose that COOH-terminal deletions of CFTR, which represent about 10% of CFTR mutations, result in defective vectorial chloride transport, partly by altering the polarized distribution of CFTR in epithelial cells. Moreover, our data demonstrate that PDZ-interacting domains and PDZ domain-containing proteins play a key role in the apical polarization of ion channels in epithelial cells.

Cloning of a cGMP-gated cation channel from mouse kidney inner medullary collecting duct.

The cDNA sequence coding for the cGMP-gated cation channel expressed in the mouse kidney inner medullary collecting duct has been determined. The kidney cGMP-gated cation channel cDNA has an open reading frame of 2055 nucleotides and encodes a 685 amino acid protein. One cDNA clone is alternatively spliced thereby producing a deletion of 107 bp. Two differentially spliced 5' untranslated regions were determined by 5' RACE.

Physical, psychologic, social, and economic outcomes after cardiac valve surgery.

Eighty-nine patients receiving cardiac valve replacement or surgery consisting of valve replacement and coronary artery bypass grafts in four teaching hospitals were studied before surgery and again six months after surgery. More than 60 indicators of the quality of life were assessed. The majority of persons showed improvement in physical function, emotional states, and social activity. Of those with exertional angina or dyspnea before surgery, about two thirds were completely relieved at six months after surgery. There was a substantial reduction in number (from 31 to seven) of persons with five or more days of disability per month due to cardiac symptoms. The majority remained the same in their usual level of physical activity, most psychological traits, and attitudes and social support networks. Most previously employed persons returned to work. Improvements in the conditions of patients who had valve surgery closely paralleled those of patients who had undergone coronary artery bypass surgery in the same hospitals.

A scale for the estimation of sleep problems in clinical research.

Problems in sleeping are widely prevalent in modern society and are often one of the presenting complaints of patients consulting physicians. In addition, there is scattered epidemiologic evidence and considerable clinical support that disturbed or inadequate sleep may be a risk factor for clinical emergence of cardiovascular disease and for total mortality. The role of sleep problems both as a precursor and as a sequela of disease states could be better delineated in large groups by the availability of a brief, reliable and standardized scale for sleep disturbance. Such a scale could also be used to evaluate the impact of different therapies upon sleep problems. This paper presents data from two study populations responding to three and four item self-report scales. From 9 to 12% of air traffic controllers reported various sleep problems to have occurred on half or more of the days during the prior month, whereas 12-22% of patients 6 months after cardiac surgery reported such frequent sleep problems. Utilizing data from the 6 and 12 month follow-ups, test-retest reliability of the three-item scale in cardiac surgery patients was found to be 0.59. Internal consistency coefficients for the three and four-item scales were 0.63 and 0.79 respectively.

Neuropsychological dysfunction following elective cardiac operation. II. A six-month reassessment.

Three neuropsychological tests were administered to 245 men and women, ages 25 to 69 years, before and 6 months after coronary bypass and cardiac valve operations to provide current information regarding the incidence of long-term postoperative decrements in neuropsychological function and the factors associated with them. Biographical, psychological and medical-surgical data were studied together with changes on the Trail Making Test from the Halstead-Reitan Battery, and Visual Reproduction (VR) and Logical Memory tests, both from the Wechsler Memory Scale (WMS). Although 28% of this group showed a deterioration in one or more test scores at a 9 day postoperative examination as compared to their preoperative scores, over 80% of these patients had returned to normal range by 6 months. Similarly, the majority of the 19% of patients showing a significant decrease in one or more of four scores at 6 months had incurred their performance decrements subsequent to the 9 day examination. Hence it seems inappropriate to attribute these latter dysfunctions to the surgical epidose per se, as others have reported. Only 5% of patients showed consistent postoperative test score deterioration both at 9 days and 6 months. Decrements of function at 6 months appear to be associated with total estimated blood loss greater than 3,000 ml and administration of propranolol during the operation plus several postoperative factors including higher levels of fatigue, depression, and worries related to the operation and the recovery process. These findings underscore the need for clinicians and investigators studying neuropsychological dysfunction following cardiac operations to take concurrent emotional and physical states into account, and to make repeated measures well separated in time, before interpreting the presence or absence of residual neuropsychological problems.

Neuropsychological dysfunction following elective cardiac operation. I. Early assessment.

Two neuropsychological tests were administered to 227 men and women, ages 25 to 69 years, before and after coronary bypass and cardiac valve operations to provide current information regarding the incidence of postoperative decrements in neuropsychological dysfunction and the factors associated with them. Biographical, psychological, and medical-surgical data were studied together with changes in scores on the Trail Making Tests and the Visual Reproduction (VR) Test of the Wechsler Memory Scale (WMS). Postoperative decrements greater than one standard deviation were observed in each of the four scores derived from these testings for 11% to 17% of the patients. Yet 70% of all patients remained within one standard deviation of original performance on all four scores. Among the preoperative correlates of significantly reduced test performance were age greater than 60 years, end-diastolic pressure greater than 30 mm Hg, moderate to severely enlarged heart size on preoperative x-ray film, and use of propranolol or chlordiazepoxide hydrochloride. Significant perioperative correlates included measure of duration of operation (such as total time of operation greater than 7 hours, time on the pump greater than 2 hours, and aortic cross-clamp time greater than 2 hours), total estimate of blood loss greater than 2,000 ml, hypotension, difficult intubation, and insertion of an intra-aortic balloon. Postoperative factors significantly associated with declines in test scores included electrolyte (Na+, K+, Cl-) abnormalities, longer stay in the intensive care unit, bizarre behavior or disorientation, and depression score. These findings suggest that those patients with more precarious heart function, a more protracted operation, and/or increased metabolic disturbances are especially prone to neuropsychological dysfunction following cardiac operations.

Functional benefits following coronary artery bypass graft surgery.

While some studies of patients who undergo cardiac surgery have included such outcome measures as amounts of symptom reduction and rates of resumption of employment, little attention has been focused on the extent to which these patients have experienced the simple, yet very important, broad range of functional benefits that might be anticipated by clinicians to result from operation. The present report seeks to document the extent of improvement that does exist in terms of physical, sexual, and social-role functioning. In a cohort of 340 patients (age, 32 to 69 years) studied before and six months after coronary artery bypass operation, improvements were noted in each of three dimensions of functional benefit: physical functioning (fewer total activity restrictions or incapacitated days per month), sexual functioning (through increased energy and desire and decreased pain and worry), and role functions (ability to work, social participation, and pursuit of hobbies). Further improvements might be anticipated with additional months of recovery.

The measurement of health-related quality of life: major dimensions identified by factor analysis.

The measurement of quality of life is becoming more important in the evaluation of medical technologies and pharmaceuticals. Particularly when the several available therapies have similar effects on survival, quality of life measures may help decide which should be the therapy of choice. The Recovery Study utilized a multidisciplinary array of indicators of health-related quality of life and recovery. This paper reports factor analyses of 58 outcome measures on a study group of 469 persons who had undergone coronary artery bypass or cardiac valve surgery 6-months previously. The factor analyses revealed 5 orthogonal dimensions. We have named them: low morale, symptoms of illness, neuropsychological function, interpersonal relationships, and economic-employment. The data argue that health-related quality of life is a multidimensional construct, and that these dimensions can be measured quantitatively with relatively simple interview and questionnaire approaches. The next research step is to determine whether the five dimensions of post-operative quality of life have different pre-operative predictors, and whether intervention on these predictors can improve the recovery and rehabilitation process.

Employment changes among patients following coronary bypass surgery: social, medical, and psychological correlates.

The relations of socioeconomic and psychological factors to resumption of employment following coronary artery bypass surgery were studied using a questionnaire returned by a sample of 426 men and 70 women. The sample was drawn from the membership of Mended Hearts, Inc., a nationwide voluntary organization of persons who have had heart surgery. Preoperatively, more men (92 percent) than women (59 percent) were employed. Return to work rates were high for men (81 percent) and much lower for women (58 percent). The 395 men tended to return to work an average of 3.7 months after surgery whereas the 41 women took an average of 4.8 months. Return to work following surgery was most clearly related to socioeconomic level for both sexes. In addition, for men, those most likely to return had less postoperative morbidity and held jobs requiring little physical exertion. Patients who reported that they were forced into an early retirement represent a particularly vulnerable group in that they were more likely to experience the most postoperative morbidity. As a group, they believed that their physicians had least prepared them to return to work, and they experienced the poorest emotional adjustment. Thus, women and those forced into early retirement represent two potentially high-risk groups of patients who would seem to require additional clinical and psychological management following surgery.

Predicting completeness of symptom relief after major heart surgery.

The authors hypothesized that the same biopsychosocial factors that raise the risk of illness incidence would influence the speed and completeness of relief from physical symptoms during recovery following cardiac surgery. This multicenter prospective study involved 463 patients aged 35 to 69 years who underwent coronary artery bypass graft or cardiac valve surgery. Predictor data were gathered 1 to 3 days before surgery, and outcome measures were collected 6 months postoperatively. The following predictors were associated with postoperative freedom from cardiac symptoms: fewer preoperative cardiac hospitalizations; low levels of angina, dyspnea, fatigue, and sleep problems; low levels of anxiety, depression, hostility, and life-change events; and high levels of psychosocial well-being, hopefulness, overall satisfaction, and social support. The predictors of not requiring daytime bed rest because of cardiac symptoms during the 6th postoperative month were male gender, higher education, less cardiac disability preoperatively, low levels of angina, dyspnea, sleep problems, depression and fatigue, and absence of Type A behavior and of intraoperative hypotension. By using separate multiple logistic regression equations, the authors identified the variables printed in bold face as independent significant contributors to prediction. Many of the predictors are strong enough and simple enough to be used in clinical practice. Many of them may also predict recovery after acute illnesses and injuries involving other organ systems.

Cystic fibrosis transmembrane conductance regulator (CFTR) and renal function.

The cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel is expressed in all nephron segments. Although mutations in CFTR are not associated with major changes in renal function, drug excretion by the kidneys is altered in cystic fibrosis (CF) as is the ability of the kidneys to concentrate and dilute the urine and excrete a salt load. It is not clear if these changes in renal function are secondary to decreased extracellular fluid volume caused by excessive losses of NaCl in sweat and feces or if they are related to primary defects in renal function caused by mutations in CFTR. Considerable evidence supports a role for CFTR in mediating Cl- secretion by the distal tubule, principal cells in the cortical collecting duct (CCD) and the inner medullary collecting duct (IMCD). In addition, CFTR is responsible for Cl- secretion into the lumen of cysts in polycystic kidneys and, therefore, contributes to cyst enlargement. Under some conditions--when Na+ absorption across the apical membrane of principal cells in the CCD is stimulated and the apical membrane potential is depolarized--the electrochemical gradient for Cl- will support Cl- absorption via CFTR Cl- channels. In addition to its function as a 3',5'-cAMP-activated Cl- channel, CFTR may play a role in intracellular vesicle acidification, protein processing, protein trafficking, secretion of ATP and the regulation of the epithelial Na channel (ENaC) and the secretory K+ channel (ROMK2) which mediate Na+ and K+ transport, respectively, across the CCD. Thus, CFTR may regulate Na+ and K+ excretion by the kidneys. The most common mutation in CFTR is delta F508, a mutation which causes improper folding of CFTR such that it is retained within the endoplasmic reticulum where it is degraded. Thus, in the majority of cases, CF is a trafficking disease. However, nothing is known about the intracellular trafficking of CFTR in the kidney. In preliminary studies we have developed a living cell model to study the intracellular trafficking of CFTR and delta F508-CFTR in renal epithelial cells in real time. Our ultimate goal is to elucidate the intracellular trafficking of CFTR and to identify therapeutic approaches to restore normal function to renal cells in CF and to block CFTR-mediated Cl- secretion in cysts in polycystic kidneys.

Serial analysis of the gut and respiratory microbiome in cystic fibrosis in infancy: interaction between intestinal and respiratory tracts and impact of nutritional exposures.

UNLABELLED: Pulmonary damage caused by chronic colonization of the cystic fibrosis (CF) lung by microbial communities is the proximal cause of respiratory failure. While there has been an effort to document the microbiome of the CF lung in pediatric and adult patients, little is known regarding the developing microflora in infants. We examined the respiratory and intestinal microbiota development in infants with CF from birth to 21 months. Distinct genera dominated in the gut compared to those in the respiratory tract, yet some bacteria overlapped, demonstrating a core microbiota dominated by Veillonella and Streptococcus. Bacterial diversity increased significantly over time, with evidence of more rapidly acquired diversity in the respiratory tract. There was a high degree of concordance between the bacteria that were increasing or decreasing over time in both compartments; in particular, a significant proportion (14/16 genera) increasing in the gut were also increasing in the respiratory tract. For 7 genera, gut colonization presages their appearance in the respiratory tract. Clustering analysis of respiratory samples indicated profiles of bacteria associated with breast-feeding, and for gut samples, introduction of solid foods even after adjustment for the time at which the sample was collected. Furthermore, changes in diet also result in altered respiratory microflora, suggesting a link between nutrition and development of microbial communities in the respiratory tract. Our findings suggest that nutritional factors and gut colonization patterns are determinants of the microbial development of respiratory tract microbiota in infants with CF and present opportunities for early intervention in CF with altered dietary or probiotic strategies. IMPORTANCE: While efforts have been focused on assessing the microbiome of pediatric and adult cystic fibrosis (CF) patients to understand how chronic colonization by these microbes contributes to pulmonary damage, little is known regarding the earliest development of respiratory and gut microflora in infants with CF. Our findings suggest that colonization of the respiratory tract by microbes is presaged by colonization of the gut and demonstrated a role of nutrition in development of the respiratory microflora. Thus, targeted dietary or probiotic strategies may be an effective means to change the course of the colonization of the CF lung and thereby improve patient outcomes.

Iron and CF-related anemia: expanding clinical and biochemical relationships.

INTRODUCTION: This cross-sectional study was conducted to assess the relationship between iron levels in the plasma and sputum of cystic fibrosis (CF) patients. METHODS: Demographic, clinical, and iron-related laboratory data were prospectively obtained from 25 patients with stable clinical features and 14 patients with worsened clinical features since their most recent evaluations. RESULTS: Compared to patients with stable clinical features, those who experienced clinical deterioration demonstrated significantly worse lung function and were more frequently malnourished and diabetic. Members of the latter group were also significantly more hypoferremic and had higher sputum iron content than patients with stable clinical features. No significant correlation was found between plasma and sputum iron levels when the groups were analyzed together and separately. CONCLUSIONS: Sputum iron content does not correlate with iron-related hematologic tests. Hypoferremia is common in CF and correlates with poor lung function and overall health.