HLA Mismatching Favoring Host-Versus-Graft NK Cell Activity Via KIR3DL1 Is Associated With Improved Outcomes Following Lung Transplantation.

Chronic lung allograft dysfunction (CLAD) is linked to rejection and limits survival following lung transplantation. HLA-Bw4 recipients of HLA-Bw6 grafts have enhanced host-versus-graft (HVG) natural killer (NK) cell activity mediated by killer cell immunoglobulin-like receptor (KIR)3DL1 ligand. Because NK cells may promote tolerance by depleting antigen-presenting cells, we hypothesized improved outcomes for HLA-Bw4 recipients of HLA-Bw6 grafts. We evaluated differences in acute cellular rejection and CLAD-free survival across 252 KIR3DL1+ recipients from University of California, San Francisco (UCSF). For validation, we assessed survival and freedom from bronchiolitis obliterans syndrome (BOS), retransplantation, or death in 12 845 non-KIR typed recipients from the United Network for Organ Sharing (UNOS) registry. Cox proportional hazards models were adjusted for age, gender, ethnicity, transplant type, and HLA mismatching. HVG-capable subjects in the UCSF cohort had a decreased risk of CLAD or death (hazard ratio [HR] 0.57, 95% confidence interval [CI] 0.36-0.88) and decreased early lymphocytic bronchitis. The HVG effect was not significant in subjects with genotypes predicting low KIR3DL1 expression. In the UNOS cohort, HVG-capable subjects had a decreased risk of BOS, retransplant, or death (HR 0.95, 95% CI 0.91-0.99). Survival improved with the higher-affinity Bw4-80I ligand and in Bw4 homozygotes. Improved outcomes in HVG-capable recipients are consistent with a protective NK cell role. Augmentation of NK activity could supplement current immunosuppression techniques.

Effect of Lung Transplantation on Health-Related Quality of Life in the Era of the Lung Allocation Score: A U.S. Prospective Cohort Study.

Under the U.S. Lung Allocation Score (LAS) system, older and sicker patients are prioritized for lung transplantation (LT). The impact of these changes on health-related quality of life (HRQL) after transplant has not been determined. In a single-center prospective cohort study from 2010 to 2016, we assessed HRQL before and repeatedly after LT for up to 3 years using the SF12-Physical and Mental Health, the respiratory-specific Airway Questionnaire 20-Revised, and the Euroqol 5D/Visual Analog Scale utility measures by multivariate linear mixed models jointly modeled with death. We also tested changes in LT-Valued Life Activities disability, BMI, allograft function, and 6-min walk test exercise capacity as predictors of HRQL change. Among 211 initial participants (92% of those eligible), LT improved HRQL by all 5 measures (p < 0.05) and all but SF12-Mental Health improved by threefold or greater than the minimally clinically important difference. Compared to younger participants, those aged ≥65 improved less in SF12-Physical and Mental Health (p < 0.01). Improvements in disability accounted for much of the HRQL improvement. In the LAS era, LT affords meaningful and durable HRQL improvements, mediated by amelioration of disability. Identifying factors limiting HRQL improvement in selected subgroups, especially those aged ≥65, are needed to maximize the net benefits of LT.

Prolonged Barium-Impaction Ileus in Two Lung Transplant Recipients With Systemic Sclerosis: Case Report.

Lung transplantation can be a life-saving measure for people with end-stage lung disease from systemic sclerosis. However, outcomes of lung transplantation may be compromised by gastrointestinal manifestations of systemic sclerosis, which can involve any part of the gastrointestinal tract. Esophageal and gastric disease can be managed by enteral feeding with the use of a gastrojejunal feeding tube. In this report, we describe the clinical courses of 2 lung transplant recipients with systemic sclerosis who experienced severe and prolonged barium-impaction ileus after insertion of a percutaneous gastrojejunal feeding tube.

Interdisciplinary pain management is beneficial for refractory orchialgia in children.

INTRODUCTION: Idiopathic testicular/groin pain can be a difficult entity for children, their families, and caregivers. The role of interdisciplinary pain management has previously been demonstrated in treating chronic orchialgia at the present pediatric pain clinic. OBJECTIVE: To evaluate the role of interdisciplinary pain management in managing refractory orchialgia. It was hypothesized that children with refractory orchialgia might respond well. Interdisciplinary care was defined as that which crosses two medical disciplines such as a surgical specialty and specialist in analgesia. SUBJECTS AND METHODS: Pediatric patients were identified who were: ≥ 10 years old; evaluated in the pediatric urology clinic between 2002 and 2012; were diagnosed wtih ICD code 608.9 or had the diagnosis of male genital disorder NOS. Children were included if they presented with orchialgia without an identifiable cause and failed conservative management (rest, scrotal support, Sitz bath, timed voiding, constipation avoidance) including conventional anti-nociceptive analgesics (acetaminophen, non-steroidal anti-inflammatory drugs, opioids). Patient electronic medical records were reviewed retrospectively. RESULTS: Twenty-two children met inclusion criteria. Mean age was 13.7 years (range 10-17). Nearly half (45%) of the children had chronic medical conditions such as asthma, allergies, and obesity. Twenty-one of the 22 children were referred to the pediatric pain clinic; 15 were evaluated, and one refused treatment. All children evaluated in the pediatric pain clinic were initially offered an empiric anti-neuropathic anti-convulsant (i.e. gabapentin) and/or an anti-depressant (i.e. amitriptyline) before being offered a nerve block. Of the 14 children accepting treatment in the pediatric pain clinic, six were treated solely with an empiric anti-neuropathic anti-convulsant and/or anti-depressant; eight received medications followed by nerve block (seven ilioinguinal-iliohypogastric blocks, one spinal and ilioinguinal-iliohypogastric block) (see Fig. 1). A total of eight of the 14 children (57%) treated by the pain clinic had resolution of pain, with 50% of those treated with medications alone (three out of six children) responding (two responding to gabapentin and a tricyclic antidepressant, one to gabapentin alone); and five out of eight (63%) treated with medications and then nerve block (ilioinguinal-iliohypogastric block) responding. Of the eight children undergoing nerve block, five required more than one block. The time between each block ranged from 4 to 22.6 weeks. Response to nerve block required an average of 1.4 procedures (range 1-2); mean follow-up after nerve block was 2.4 months (range 0.1-4.8). DISCUSSION: Children with refractory orchialgia often have comorbidities that suggest a multidisciplinary approach would be useful for treating them. The present study found that the majority of children with refractory orchialgia treated in the pediatric pain clinic responded to management. Major limitations, however, included small cohort size and short follow-up, particularly in those children undergoing nerve block. There was also no objective assessment of pain improvement or improvement in quality of life, which could be rectified with a prospective study. CONCLUSION: Collaboration and early referral for interdisciplinary pain management as one of these multidisciplinary approaches may help to coordinate care and ease patient suffering.

Bronchoalveolar lavage cell immunophenotyping facilitates diagnosis of lung allograft rejection.

Supplementary methods to identify acute rejection and to distinguish rejection from infection may improve clinical outcomes for lung allograft recipients. We hypothesized that distinct bronchoalveolar lavage (BAL) cell profiles are associated with rejection and infection. We retrospectively compared 2939 BAL cell counts and immunophenotypes against concomitantly obtained transbronchial biopsies and microbiologic studies. We randomly assigned 317 subjects to a derivation or validation cohort. BAL samples were classified into four groups: infection, rejection grade ≥A1, both or neither. We employed generalized estimating equation and survival modeling to identify clinical predictors of rejection and infection. We found that CD25(+) and natural killer cell percentages identified a twofold increased odds of rejection compared to either the infection or the neither infection nor rejection groups. Also, monocytes, lymphocytes and eosinophil percentages were independently associated with rejection. A four-predictor scoring system had high negative predictive value (96-98%) for grade ≥A2 rejection, predicted future rejection in the validation cohort and predicted increased risk of bronchiolitis obliterans syndrome in otherwise benign samples. In conclusion, BAL cell immunophenotyping discriminates between infection and acute rejection and predicts future outcomes in lung transplant recipients. Although it cannot replace histopathology, immunophenotyping may be a clinically useful adjunct.

Gastro-oesophageal reflux and aspiration in patients with advanced lung disease.

Numerous small observational studies have shown that gastro-oesophageal reflux is prevalent among patients with advanced lung disease. The fundamental concern is that reflux is a risk factor for recurrent microaspiration, which may cause lung injury. For example, in lung transplant patients, a molecular marker of aspiration was a risk factor for the bronchiolitis obliterans syndrome in one study. To date, however, there are no large prospective studies measuring the impact of aspiration on clinical outcomes. The major obstacle limiting the study of reflux and aspiration in patients with advanced lung disease is the absence of a reliable diagnostic tool. Proximal oesophageal acid detection by pH monitoring is the only widely available measure of aspiration risk. Impedance monitoring may be a superior measure of aspiration risk as it measures both acid and non-acid reflux episodes. Molecular markers of aspiration, such as pepsin or bile salts in the bronchoalveolar lavage or exhaled breath condensate, may be the optimal diagnostic tests, but they are not currently available outside the research setting. Larger observational studies are needed to determine the following: (1) the clinical significance of aspiration in patients with advanced lung disease and in patients who have had lung transplantation and (2) the diagnostic test that best predicts adverse outcomes.

Antireflux surgery for patients with end-stage lung disease before and after lung transplantation.

BACKGROUND: Gastroesophageal reflux disease (GERD) is prevalent among patients with end-stage lung disease (ESLD). This disease can lead to microaspiration and may be a risk factor for lung damage before and after transplantation. A fundoplication is the best way to stop reflux, but little is known about the safety of elective antireflux surgery for patients with ESLD. This study aimed to report the safety of laparoscopic fundoplication for patients with ESLD and GERD before or after lung transplantation. METHODS: Between January 1997 and January 2007, 305 patients were listed for lung transplantation, and 189 patients underwent the procedure. In 2003, routine esophageal studies were added to the pretransplantation evaluation. After the authors' initial experience, gastric emptying studies were added as well. RESULTS: A total of 35 patients with GERD or delayed gastric emptying were referred for surgical intervention. A laparoscopic fundoplication was performed for 32 patients (27 total and 5 partial). For three patients, a pyloroplasty also was performed. Two patients had a pyloroplasty without fundoplication. Of the 35 operations, 15 were performed before and 20 after transplantation. Gastric emptying of solids or liquids was delayed in 12 (92%) of 13 posttransplantation studies and 3 (60%) of 5 pretransplantation studies. All operations were completed laparoscopically, and 33 patients recovered uneventfully (94%). The median hospital length of stay was 2 days (range, 1-34 days) for the patients admitted to undergo elective operations. Hospitalization was not prolonged for the three patients who had fundoplications immediately after transplantation. CONCLUSIONS: The results of this study show that laparoscopic antireflux surgery can be performed safely by an experienced multidisciplinary team for selected patients with ESLD before or after lung transplantation, and that gastric emptying is frequently abnormal and should be objectively measured in ESLD patients.

Structural changes to airway smooth muscle in cystic fibrosis.

BACKGROUND: Chronic airway obstruction is characteristic of cystic fibrosis (CF) but there are few studies of airway smooth muscle remodelling in CF. METHODS: Airway smooth muscle content and mean airway smooth muscle cell size were measured by applying design-based stereology to bronchoscopic biopsy specimens obtained from seven subjects with CF and 15 healthy controls. RESULTS: The smooth muscle content increased by 63% in subjects with CF (mean (SD) 0.173 (0.08) v 0.106 (0.042) mm(3) smooth muscle/mm(3) submucosa, mean difference -0.067; 95% CI -0.12 to -0.013, p = 0.017) but there was no increase in mean cell size (2705 (351) v 2654 (757) microm(3), mean difference -51; 95% CI -687 to 585, p = 0.87). CONCLUSIONS: These findings indicate hyperplasia of airway smooth muscle cells without hypertrophy and suggest that accumulation of airway smooth muscle cells may contribute to airway narrowing and bronchial hyperresponsiveness in CF.

Allergen challenge causes inflammation but not goblet cell degranulation in asthmatic subjects.

BACKGROUND: An allergen challenge to the airways of sensitized mice causes eosinophilic airway inflammation and degranulation of goblet cells, which lead to airway obstruction. However, whether allergen challenge causes a similar pattern of airway inflammation and goblet cell degranulation in human beings is unknown. OBJECTIVE: The purpose of this study was to determine whether allergen challenge increases airway inflammatory cells and causes goblet cell degranulation in human subjects with asthma. METHODS: In bronchial biopsy specimens taken from 8 asthmatic subjects at 1 and 24 hours after allergen challenge, we measured eosinophil and neutrophil numbers as indicators of inflammation. We also measured goblet cell mucin stores and the amounts of secreted mucin in bronchial lavage as indicators of goblet cell degranulation. RESULTS: Airway eosinophil numbers at both 1 and 24 hours after allergen challenge were twice as high as those after diluent challenge. Changes in neutrophil numbers were smaller and statistically insignificant. Goblet cell mucin stores measured in tissue stained with alcian blue/periodic acid-Schiff did not decrease significantly from baseline to 1 hour and actually tended to increase at 24 hours. This increase was significant in the subgroup of subjects with normal stored mucin levels at baseline. Mucin-like glycoprotein concentrations in bronchial lavage did not change significantly at either time point. CONCLUSION: Although allergen challenge in asthmatic subjects increases airway eosinophil numbers as early as 1 hour after challenge, this inflammatory response does not cause goblet cell degranulation. In fact, in subjects with normal baseline mucin stores, allergen challenge increases goblet cell mucin stores.

Renal replacement therapy and orthotopic liver transplantation: the role of continuous veno-venous hemodialysis.

BACKGROUND: The need for renal replacement therapy (RRT) either before or after orthotopic liver transplant (OLTX) has been reported to be a poor prognostic indicator for survival. Use of continuous veno-venous hemodialysis (CVVHD) for RRT has been reported in three series of OLTX patients with high 90-day mortality rates of 57-60%. We have examined our patient population to determine the effect of necessity and type of RRT on patient survival after OLTX. METHODS: We analyzed 1535 OLTX that were performed at our institution from 1985 through 1999, 1037 from 1985 to 1995 (period I) and 498 from 1996 to 1999 (period II). Combined liver-kidney transplants were excluded from analysis. Hospital dialysis unit records and a prospectively maintained database on all OLTX patients served as the source of data. Patients were classified into groups defined on whether or not they received RRT, when they received RRT, and the type of RRT. Groups were compared for preoperative intensive care unit status, time on the waiting list, laboratory variables, 90-day postoperative mortality, 1-year patient survival, and absolute survival. RESULTS: Use of RRT increased from 8.29% in period I to 12.45% in period II, along with increased median waiting times. In period I, patients receiving preoperative RRT had a 90-day mortality (0%) and a 1-year survival (89.5%) almost identical to those patients who never required RRT (1.7% and 90.6%). Patients who developed acute renal failure postoperatively requiring RRT, however, had a 90-day mortality of 28.6% and a 1-year survival of 55%. In period II, patients requiring RRT had a 90-day mortality of 39.7% and a 1-year actuarial survival of 54.5% compared with 6.9% and 88.6% in patients never requiring RRT. Patients treated with CVVHD had a 90-day mortality of 42% compared with 25% in patients treated with hemodialysis alone. However, patients receiving CVVHD both pre- and postoperatively had a 90-day mortality of 27.7% vs. 50% in those patients who only received CVVHD postoperatively. Patients who developed acute renal failure postoperatively, which required RRT, regardless of therapy, had a 1-year survival of only 41.0% compared with a 1-year survival of 73.6% in those patients started on RRT preoperatively, P=0.03. CONCLUSIONS: The need for RRT has increased along with waiting time in OLTX patients. Patients developing the need for RRT postoperatively have an increased 90-day mortality and lower 1-year survival with the highest being present in patients receiving CVVHD, which was started postoperatively. These findings may reflect a trend toward a sicker population awaiting OLTX and emphasize the negative impact of renal failure on survival after OLTX.

End-stage renal disease (ESRD) after orthotopic liver transplantation (OLTX) using calcineurin-based immunotherapy: risk of development and treatment.

BACKGROUND: The calcineurin inhibitors cyclosporine and tacrolimus are both known to be nephrotoxic. Their use in orthotopic liver transplantation (OLTX) has dramatically improved success rates. Recently, however, we have had an increase of patients who are presenting after OLTX with end-stage renal disease (ESRD). This retrospective study examines the incidence and treatment of ESRD and chronic renal failure (CRF) in OLTX patients. METHODS: Patients receiving an OLTX only from June 1985 through December of 1994 who survived 6 months postoperatively were studied (n=834). Our prospectively collected database was the source of information. Patients were divided into three groups: Controls, no CRF or ESRD, n=748; CRF, sustained serum creatinine >2.5 mg/dl, n=41; and ESRD, n=45. Groups were compared for preoperative laboratory variables, diagnosis, postoperative variables, survival, type of ESRD therapy, and survival from onset of ESRD. RESULTS: At 13 years after OLTX, the incidence of severe renal dysfunction was 18.1% (CRF 8.6% and ESRD 9.5%). Compared with control patients, CRF and ESRD patients had higher preoperative serum creatinine levels, a greater percentage of patients with hepatorenal syndrome, higher percentage requirement for dialysis in the first 3 months postoperatively, and a higher 1-year serum creatinine. Multivariate stepwise logistic regression analysis using preoperative and postoperative variables identified that an increase of serum creatinine compared with average at 1 year, 3 months, and 4 weeks postoperatively were independent risk factors for the development of CRF or ESRD with odds ratios of 2.6, 2.2, and 1.6, respectively. Overall survival from the time of OLTX was not significantly different among groups, but by year 13, the survival of the patients who had ESRD was only 28.2% compared with 54.6% in the control group. Patients developing ESRD had a 6-year survival after onset of ESRD of 27% for the patients receiving hemodialysis versus 71.4% for the patients developing ESRD who subsequently received kidney transplants. CONCLUSIONS: Patients who are more than 10 years post-OLTX have CRF and ESRD at a high rate. The development of ESRD decreases survival, particularly in those patients treated with dialysis only. Patients who develop ESRD have a higher preoperative and 1-year serum creatinine and are more likely to have hepatorenal syndrome. However, an increase of serum creatinine at various times postoperatively is more predictive of the development of CRF or ESRD. New strategies for long-term immunosuppression may be needed to decrease this complication.

Is there an adaptive response to radiation in the developing brain of the fetal rat?

An adaptive response has been demonstrated in certain mammalian cells wherein pre-exposure to a small radiation dose prior to a large dose ameliorates the damage induced by the second dose. We investigated whether a similar response could occur in the developing brain of the fetal rat, and if so, what the optimum interval between the two doses would be. Pregnant rats were exposed to a dose of 0.02 Gy gamma radiation at variable times (1, 3, 6, 12, or 24 h) prior to a second dose of 0.5 Gy on day 15 of gestation. Fetuses were harvested at 6 and 24 h after the second irradiation and standard cellular morphological assessments performed on the developing cerebral cortex. For number of mitotic cells, pyknotic cells, and macrophages, no significant differences were found between any of the groups that had received the priming (0.02 Gy) dose and the group that had not. Significant differences were found between fetuses harvested at 6 h and those harvested at 24 h after the final irradiation for all parameters measured. Thus, while the data were consistent with past research relating to the effects of radiation on the development of the brain of the fetal rat, no evidence for an adaptive response to radiation was found. Whether an adaptive response was indeed absent, or whether the doses and/or intervals used were simply not appropriate for demonstrating it, remains unknown.

Ischemic acute renal failure.

Underperfusion of the kidneys often results in the development of ischemic acute renal failure. This review summarizes the recent developments in the understanding of the pathophysiology, diagnosis, and treatment of this serious and costly disorder that affects almost 5% of hospitalized patients.

Mineralocorticoid modulation of apical and basolateral membrane H+/OH-/HCO3- transport processes in the rabbit inner stripe of outer medullary collecting duct.

To examine the mechanism by which mineralocorticoids regulate HCO3- absorption in the rabbit inner stripe of the outer medullary collecting duct, we microfluorometrically measured intracellular pH (pHi) in in vitro perfused tubules using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) assaying the apical and basolateral membrane H+/OH-/HCO3- transport processes in three groups of animals: those receiving chronic in vivo DOCA treatment (5 mg/kg per d x 2 wk); those with surgical adrenalectomy (ADX, [chronic x 2 wk]) on glucocorticoid replacement; and controls. Baseline pHi was not different in the three groups. Cellular volume (vol/mm) was increased 38% in DOCA tubules versus controls, but unchanged in ADX tubules versus controls. Buffer capacities (BT) were not different in the three groups. Apical membrane H+ pump activity, assayed as the Na(+)-independent pHi recovery from an acid load (NH3/NH4+ prepulse) and expressed as JH (dpHi/dt.vol/mm.BT) was increased 76% in DOCA tubules versus controls, and decreased 56% in ADX tubules versus controls. Basolateral membrane Cl-/HCO3- exchange activity assayed as the pHi response to basolateral Cl- addition was increased 73% in DOCA tubules versus controls, and decreased 44% in ADX tubules versus controls. When examined as a function of varying [Cl-], the Vmax of Cl-/HCO3- exchange activity was significantly increased in DOCA tubules (control, 72.7 +/- 15.7 pmol.mm-1.min-1 vs DOCA, 132.3 +/- 22.5 pmol.mm-1.min-1, P less than 0.02), while the K1/2 for Cl- was unchanged. Basolateral membrane Na+/H+ antiporter activity assayed as the Na(+)-dependent pHi recovery from an acid load was not changed in chronic DOCA tubules versus controls. In conclusion, the apical membrane H+ pump and basolateral membrane Cl-/HCO3- exchanger of the rabbit OMCDi are regulated in parallel without chronic alterations in pHi under the conditions of mineralocorticoid excess and deficiency. The parallel changes in these transporters accounts for the alterations in OMCDi HCO3- absorption seen under these conditions.

Inhibition of Na(+)-independent H+ pump by Na(+)-induced changes in cell Ca2+.

Apical membrane H+ extrusion in the renal outer medullary collecting duct, inner stripe, is mediated by a Na(+)-independent H+ pump. To examine the regulation of this transporter, cell pH and cell Ca2+ were measured microfluorometrically in in vitro perfused tubules using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein and fura-2, respectively. Apical membrane H+ pump activity, assayed as cell pH recovery from a series of acid loads (NH3/NH+4 prepulse) in the total absence of ambient Na+, initially occurred at a slow rate (0.06 +/- 0.02 pH units/min), which was not sufficient to account for physiologic rates of H+ extrusion. Over 15-20 min after the initial acid load, the rate of Na(+)-independent cell pH recovery increased to 0.63 +/- 0.09 pH units/min, associated with a steady-state cell pH greater than the initial pre-acid load cell pH. This pattern suggested an initial suppression followed by a delayed activation of the apical membrane H+ pump. Replacement of peritubular Na+ with choline or N-methyl-D-glucosamine resulted in an initial spike increase in cell Ca2+ followed by a sustained increase in cell Ca2+. The initial rate of Na(+)-independent cell pH recovery could be increased by elimination of the Na+ removal-induced sustained cell Ca2+ elevation by: (a) performing studies in the presence of 135 mM peritubular Na+ (1 mM peritubular amiloride used to inhibit basolateral membrane Na+/H+ antiport); (b) clamping cell Ca2+ low with dimethyl-BAPTA, an intracellular Ca2+ chelating agent; or (c) removal of extracellular Ca2+. Cell acidification induced a spike increase in cell Ca2+. The late acceleration of Na(+)-independent cell pH recovery was independent of Na+ removal and of the method used to acidify the cell, but was eliminated by prevention of the cell Ca2+ spike and markedly delayed by the microfilament-disrupting agent, cytochalasin B. This study demonstrates that peritubular Na+ removal results in a sustained elevation in cell Ca2+, which inhibits the apical membrane H+ pump. In addition, rapid cell acidification associated with a spike increase in cell Ca2+ leads to a delayed activation of the H+ pump. Thus, cell Ca2+ per se, or a Ca(2+)-activated pathway, can modulate H+ pump activity.

Apical and basolateral membrane H+ extrusion mechanisms in inner stripe of rabbit outer medullary collecting duct.

To examine mechanisms of H+ extrusion in the inner stripe of outer medullary collecting duct (OMCDIS), cell pH (pHi) was measured microfluorometrically in in vitro perfused tubules by use of 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. In total absence of luminal and peritubular Na+, pHi recovery from an acid load (NH3/NH+4 pulse) occurred at an initial rate of 0.13 +/- 0.02 pH units/min, whereas in the presence of 135 mM peritubular Na+, pHi recovered at 1.40 +/- 0.28 pH units/min. Na(+)-dependent pHi recovery was completely inhibited by 1.0 mM peritubular amiloride. Luminal Na+ (135 mM) addition had no effect on pHi recovery. Na(+)-independent pHi recovery from acid load was manifest by a triphasic response: 1) initial slow alkalinization; 2) slow cell acidification; and 3) a final phase that exhibited gradually increasing rates of alkalinization, returning pHi above the initial control level (pre-NH3/NH+4 pulse). Luminal N-ethylmaleimide (NEM, 500 microM), an H(+)-ATPase inhibitor, significantly inhibited initial rate of pHi recovery and total pHi recovery; whereas 500 microM peritubular NEM had no effect on initial rate of pHi recovery. Luminal SCH 28080 (100 microM), an H(+)-K(+)-ATPase inhibitor, had no effect on initial rate of pHi recovery or total pHi recovery. Thus rabbit OMCDIS possesses both an apical membrane NEM-sensitive, SCH 28080-insensitive, Na(+)-independent H+ extrusion mechanism (likely a simple H(+)-translocating ATPase) and a basolateral membrane amiloride-sensitive Na(+)-H+ antiporter.