SWI/SNF chromatin remodeling complex in pancreatic ductal adenocarcinoma: Clinicopathologic and immunohistochemical study

The SWItch/Sucrose Non-Fermentable (SWI/SNF) complex is a multimeric protein involved in transcription regulation and DNA damage repair. SWI/SNF complex abnormalities are observed in approximately 14-34 % of pancreatic ductal adenocarcinomas (PDACs). Herein, we evaluated the immunohistochemical expression of a subset of the SWI/SNF complex proteins (ARID1A, SMARCA4/BRG1, SMARCA2/BRM, and SMARCB1/INI1) within our PDAC tissue microarray to determine whether SWI/SNF loss is associated with any clinicopathologic features or patient survival in PDAC. In our cohort, 13 of 353 (3.7 %) PDACs showed deficient SWI/SNF complex expression, which included 11 (3.1 %) with ARID1A loss, 1 (0.3 %) with SMARCA4/BRG1 loss, and 1 (0.3 %) with SMARCA2/BRM loss. All cases were SMARCB1/INI1 proficient. The SWI/SNF-deficient PDACs were more frequently identified in older patients with a mean age of 71.6 years (SD = 7.78) compared to the SWI/SNF-proficient PDACs which occurred at a mean age of 65.2 years (SD = 10.95) (P = 0.013). The SWI/SNF-deficient PDACs were associated with higher histologic grade, compared to the SWI/SNF-proficient PDACs (P = 0.029). No other significant clinicopathologic differences were noted between SWI/SNF-deficient and SWI/SNF-proficient PDACs. On follow-up, no significant differences were seen for overall survival and progression-free survival between SWI/SNF-deficient and SWI/SNF-proficient PDACs (both with P > 0.05). In summary, SWI/SNF-deficient PDACs most frequently demonstrate ARID1A loss. SWI/SNF-deficient PDACs are associated with older age and higher histologic grade. No other significant associations among other clinicopathologic parameters were seen in SWI/SNF-deficient PDACs including survival.

Targeted Next-Generation Sequencing Improves the Prognostication of Patients with Disseminated Appendiceal Mucinous Neoplasms (Pseudomyxoma Peritonei)

BACKGROUND

Appendiceal mucinous neoplasms (AMNs) with disseminated disease (pseudomyxoma peritonei) are heterogeneous tumors with variable clinicopathologic behavior. Despite the development of prognostic systems, objective biomarkers are needed to stratify patients. With the advent of next-generation sequencing (NGS), it remains unclear if molecular testing can improve the evaluation of disseminated AMN patients.

METHODS

Targeted NGS was performed for 183 patients and correlated with clinicopathologic features to include American Joint Committee on Cancer/World Health Organization (AJCC/WHO) histologic grade, peritoneal cancer index (PCI), completeness of cytoreduction (CC) score, and overall survival (OS).

RESULTS

Genomic alterations were identified for 179 (98%) disseminated AMNs. Excluding mitogen-activated protein kinase genes and GNAS due to their ubiquitous nature, collective genomic alterations in TP53, SMAD4, CDKN2A, and the mTOR genes were associated with older mean age, higher AJCC/WHO histologic grade, lymphovascular invasion, perineural invasion, regional lymph node metastasis, and lower mean PCI (p < 0.040). Patients harboring TP53, SMAD4, ATM, CDKN2A, and/or mTOR gene alterations were found to have lower OS rates of 55% at 5 years and 14% at 10 years, compared with 88% at 5 years and 88% at 10 years for patients without the aforementioned alterations (p < 0.001). Based on univariate and multivariate analyses, genomic alterations in TP53, SMAD4, ATM, CDKN2A, and/or the mTOR genes in disseminated AMNs were a negative prognostic factor for OS and independent of AJCC/WHO histologic grade, PCI, CC score, and hyperthermic intraperitoneal chemotherapy treatment (p = 0.006).

CONCLUSIONS

Targeted NGS improves the prognostic assessment of patients with disseminated AMNs and identifies patients who may require increased surveillance and/or aggressive management.

A Combined DNA/RNA-based Next-Generation Sequencing Platform to Improve the Classification of Pancreatic Cysts and Early Detection of Pancreatic Cancer Arising From Pancreatic Cysts

OBJECTIVE

We report the development and validation of a combined DNA/RNA next-generation sequencing (NGS) platform to improve the evaluation of pancreatic cysts.

BACKGROUND AND AIMS

Despite a multidisciplinary approach, pancreatic cyst classification, such as a cystic precursor neoplasm, and the detection of high-grade dysplasia and early adenocarcinoma (advanced neoplasia) can be challenging. NGS of preoperative pancreatic cyst fluid improves the clinical evaluation of pancreatic cysts, but the recent identification of novel genomic alterations necessitates the creation of a comprehensive panel and the development of a genomic classifier to integrate the complex molecular results.

METHODS

An updated and unique 74-gene DNA/RNA-targeted NGS panel (PancreaSeq Genomic Classifier) was created to evaluate 5 classes of genomic alterations to include gene mutations (e.g., KRAS, GNAS, etc.), gene fusions and gene expression. Further, CEA mRNA ( CEACAM5 ) was integrated into the assay using RT-qPCR. Separate multi-institutional cohorts for training (n=108) and validation (n=77) were tested, and diagnostic performance was compared to clinical, imaging, cytopathologic, and guideline data.

RESULTS

Upon creation of a genomic classifier system, PancreaSeq GC yielded a 95% sensitivity and 100% specificity for a cystic precursor neoplasm, and the sensitivity and specificity for advanced neoplasia were 82% and 100%, respectively. Associated symptoms, cyst size, duct dilatation, a mural nodule, increasing cyst size, and malignant cytopathology had lower sensitivities (41-59%) and lower specificities (56-96%) for advanced neoplasia. This test also increased the sensitivity of current pancreatic cyst guidelines (IAP/Fukuoka and AGA) by >10% and maintained their inherent specificity.

CONCLUSIONS

PancreaSeq GC was not only accurate in predicting pancreatic cyst type and advanced neoplasia but also improved the sensitivity of current pancreatic cyst guidelines.

Goblet cell adenocarcinoma of the appendix: an update and practical approach to diagnosis and grading

Goblet cell adenocarcinoma is a rare appendiceal tumour with amphicrine differentiation that has distinct morphologic and clinical features compared to carcinomas seen elsewhere in the gastrointestinal tract. These tumors have engendered considerable confusion in the literature regarding their classification, and they have been described under several different names including goblet cell carcinoid, adenocarcinoid, and adenocarcinoma, among others. In the recent fifth edition of the World Health Organization Classification of Digestive System Tumors, goblet cell adenocarcinoma is the preferred diagnosis because of the increasing recognition of a frequent co-existing high-grade adenocarcinoma component. This review will present the clinicopathologic, molecular, and immunohistochemical features of goblet cell adenocarcinoma and discuss the current challenges in diagnosis, grading, and clinical management.

Prospective, Multi-Institutional, Real-Time Next-Generation Sequencing of Pancreatic Cyst Fluid Reveals Diverse Genomic Alterations That Improve the Clinical Management of Pancreatic Cysts

BACKGROUND & AIMS

Next-generation sequencing (NGS) of pancreatic cyst fluid is a useful adjunct in the assessment of patients with pancreatic cyst. However, previous studies have been retrospective or single institutional experiences. The aim of this study was to prospectively evaluate NGS on a multi-institutional cohort of patients with pancreatic cyst in real time.

METHODS

The performance of a 22-gene NGS panel (PancreaSeq) was first retrospectively confirmed and then within a 2-year timeframe, PancreaSeq testing was prospectively used to evaluate endoscopic ultrasound-guided fine-needle aspiration pancreatic cyst fluid from 31 institutions. PancreaSeq results were correlated with endoscopic ultrasound findings, ancillary studies, current pancreatic cyst guidelines, follow-up, and expanded testing (Oncomine) of postoperative specimens.

RESULTS

Among 1933 PCs prospectively tested, 1887 (98%) specimens from 1832 patients were satisfactory for PancreaSeq testing. Follow-up was available for 1216 (66%) patients (median, 23 months). Based on 251 (21%) patients with surgical pathology, mitogen-activated protein kinase/GNAS mutations had 90% sensitivity and 100% specificity for a mucinous cyst (positive predictive value [PPV], 100%; negative predictive value [NPV], 77%). On exclusion of low-level variants, the combination of mitogen-activated protein kinase/GNAS and TP53/SMAD4/CTNNB1/mammalian target of rapamycin alterations had 88% sensitivity and 98% specificity for advanced neoplasia (PPV, 97%; NPV, 93%). Inclusion of cytopathologic evaluation to PancreaSeq testing improved the sensitivity to 93% and maintained a high specificity of 95% (PPV, 92%; NPV, 95%). In comparison, other modalities and current pancreatic cyst guidelines, such as the American Gastroenterology Association and International Association of Pancreatology/Fukuoka guidelines, show inferior diagnostic performance. The sensitivities and specificities of VHL and MEN1/loss of heterozygosity alterations were 71% and 100% for serous cystadenomas (PPV, 100%; NPV, 98%), and 68% and 98% for pancreatic neuroendocrine tumors (PPV, 85%; NPV, 95%), respectively. On follow-up, serous cystadenomas with TP53/TERT mutations exhibited interval growth, whereas pancreatic neuroendocrine tumors with loss of heterozygosity of ≥3 genes tended to have distant metastasis. None of the 965 patients who did not undergo surgery developed malignancy. Postoperative Oncomine testing identified mucinous cysts with BRAF fusions and ERBB2 amplification, and advanced neoplasia with CDKN2A alterations.

CONCLUSIONS

PancreaSeq was not only sensitive and specific for various pancreatic cyst types and advanced neoplasia arising from mucinous cysts, but also reveals the diversity of genomic alterations seen in pancreatic cysts and their clinical significance.

Integrating Molecular Analysis into the Pathologic Evaluation of Pancreatic Cysts

The development of cross-sectional imaging techniques has enhanced the detection of pancreatic cystic lesions (PCLs). PCLs are found in approximately 2% of the general population, often as incidentally detected lesions on computed tomography or MRI during the evaluation of other medical conditions. Broadly, PCLs are classified as mucinous or nonmucinous. Mucinous PCLs include mucinous cystic neoplasms and intraductal papillary mucinous neoplasms. Nonmucinous PCLs include pseudocysts, serous cystadenomas, solid pseudopapillary neoplasms, and cystic pancreatic neuroendocrine tumors, as well as cystic acinar cell carcinoma, cystic degeneration of pancreatic ductal adenocarcinoma, lymphoepithelial cyst, and others.

Immune Response in Colorectal Carcinoma: A Review of Its Significance as a Predictive and Prognostic Biomarker

Colorectal carcinoma is a leading cause of cancer-related death worldwide. There is significant prognostic heterogeneity in stage II and III tumours, necessitating the development of new biomarkers to better identify patients at risk of disease progression. Recently, the tumour immune environment, particularly the type and quantity of T lymphocytes, has been shown to be a useful biomarker in predicting prognosis for patients with colorectal carcinoma. In this review, the significance of the immune response in colorectal carcinoma, including its influence on prognosis and response to therapy, will be detailed.

Abstract 1930: Unsupervised sub-cellular segmentation of complex tissue and cell samples using highly multiplexed imaging-derived a priori knowledge

Spatial context of heterocellular interactions within solid tumor microenvironments (TMEs) is important for deciphering the mechanistic underpinnings of malignant TME phenotypes and leveraging that knowledge to improve personalized and precision medicine. Recent development of highly multiplexed imaging approaches, such as co-detection by indexing (CODEX), cyclic immunofluorescence (cycif), and imaging mass cytometry (IMC) has, for the first time, allowed deep interrogation of this heterocellular spatial complexity. Proper quantitation of this complexity, however, requires the ability to easily and accurately segment and localize cells and their sub-cellular compartments within the spatial context of the tumor microenvironment. Seminal approaches based on semi-supervised and supervised learning methods, including deep learning techniques, have been developed to segment cells and their nuclei. However, generalization of these methods to segmenting heterogenous and complex cell and tissue samples with varying resolution, magnification, and dynamic range, remains a persistent bottleneck. In case of deep learning, the requirement of large and accurate annotated datasets further adds to the challenge of seamless integration of systems-based methods in pathology and cancer research. Here, we demonstrate that by leveraging cell-compartment specific a priori knowledge captured by these imaging modalities, we can segment cells in complex tissue and cell samples in an unsupervised manner, without requiring model training. We specifically show that using nucleus and cell-membrane markers, we can accurately segment sub-cellular compartments of a diversity of tissue samples imaged at different resolutions, magnifications and dynamic ranges, and cell samples at varying levels of confluency. We also demonstrate that our method is fast. Given its ease of use, accuracy, robustness, and no requirement of large, annotated datasets, our unsupervised segmentation method fills a much-needed gap toward integration of spatial systems biology and cancer research within the convergence science paradigm.

Citation Format: Bogdan Kochetov, Phoenix D. Bell, Rebecca Raphael, Benjamin J. Raymond, Brian J. Leibowitz, Jingshan Tong, Brenda Diergaarde, Jian Yu, Reetesh K. Pai, Robert E. Schoen, Lin Zhang, Aatur Singhi, Shikhar Uttam. Unsupervised sub-cellular segmentation of complex tissue and cell samples using highly multiplexed imaging-derived a priori knowledge [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1930.

The Clinical Significance of Perineural Invasion by Prostate Cancer on Needle Core Biopsy

CONTEXT.—

Perineural invasion (PNI) by prostate cancer has been associated with adverse pathology, including extraprostatic extension. However, the significance of PNI quantification on prostate biopsy (PBx) remains unclear.

OBJECTIVE.—

To compare radical prostatectomy (RP) findings and long-term outcomes in patients whose PBx had exhibited PNI.

DESIGN.—

We assessed 497 consecutive patients undergoing sextant (6-site/≥12-core) PBx showing conventional adenocarcinoma followed by RP.

RESULTS.—

PNI was found in 1 (n = 290)/2 (n = 132)/3 (n = 47)/4 (n = 19)/5 (n = 5)/6 (n = 4) of the sites/regions of PBx. Compared with a single PNI site, multiple PNIs were significantly associated with higher preoperative prostate-specific antigen, higher Grade Group (GG) on PBx or RP, higher pT or pN category, positive surgical margin, and larger estimated tumor volume. When compared in subgroups of patients based on PBx GG, significant differences in RP GG (GG1-3), pT (GG1-2/GG1-3/GG2/GG3), surgical margin status (GG1-3/GG3/GG5), or tumor volume (GG1-2/GG1-3/GG2/GG3) between 1 versus multiple PNIs were observed. Moreover, there were significant differences in prostate-specific antigen (PNI sites: 1-2 versus 3-6/1-3 versus 4-6/1-4 versus 5-6), RP GG (1-3 versus 4-6/1-4 versus 5-6), pT (1-2 versus 3-6/1-3 versus 4-6), pN (1-3 versus 4-6), or tumor volume (1-2 versus 3-6/1-4 versus 5-6). Outcome analysis revealed significantly higher risks of disease progression in the entire cohort or PBx GG1-2/GG1-3/GG2/GG3/GG5 cases showing 2 to 6 PNIs, compared with respective controls with 1-site PNI. In multivariate analysis, multisite PNI was an independent predictor for progression (hazard ratio = 1.556, P = .03).

CONCLUSIONS.—

Multiple sites of PNI on PBx were associated with worse histopathologic features in RP specimens and poorer prognosis. PNI may thus need to be specified, if present, in every sextant site on PBx, especially those showing GG1-3 cancer.

Limited Adenocarcinoma of the Prostate on Needle Core Biopsy

CONTEXT.—

Grading small foci of prostate cancer on a needle biopsy is often difficult, yet the clinical significance of accurate grading remains uncertain.

OBJECTIVE.—

To assess if grading of limited adenocarcinoma on prostate biopsy specimen is critical.

DESIGN.—

We studied 295 consecutive patients undergoing extended-sextant biopsy with only 1-core involvement of adenocarcinoma, followed by radical prostatectomy.

RESULTS.—

The linear tumor lengths on these biopsy specimens were: less than 1 mm (n = 114); 1 mm or more or less than 2 mm (n = 82); 2 mm or more or less than 3 mm (n = 35); and 3 mm or more (n = 64). Longer length was strongly associated with higher Grade Group (GG) on biopsy or prostatectomy specimen, higher risk of extraprostatic extension/seminal vesicle invasion and positive surgical margin, and larger estimated tumor volume. When cases were compared based on biopsy specimen GG, higher grade was strongly associated with higher prostatectomy specimen GG, higher incidence of pT3/pT3b disease, and larger tumor volume. Outcome analysis further showed significantly higher risks for biochemical recurrence after radical prostatectomy in patients with 1 mm or more, 2 mm or more, 3 mm or more, GG2-4, GG3-4, GG4, less than 1 mm/GG2-4, less than 1 mm/GG3-4, less than 2 mm/GG3-4, 3 mm or more/GG2-4, or 3 mm or more/GG3-4 tumor on biopsy specimens, compared with respective control subgroups. In particular, 3 mm or more, GG3, and GG4 on biopsy specimens showed significance as independent prognosticators by multivariate analysis. Meanwhile, there were no significant differences in the rate of upgrading or downgrading after radical prostatectomy among those subgrouped by biopsy specimen tumor length (eg, <1 mm [44.7%] versus ≥1/<2 mm [41.5%] versus ≥2/<3 mm [45.7%] versus ≥3 mm [46.9%]).

CONCLUSIONS.—

These results indicate that pathologists still need to make maximum efforts to grade relatively small prostate cancer on biopsy specimens.

Clinicopathologic features of metastatic small cell carcinoma of the prostate to the liver: a series of four cases

BACKGROUND

Small cell neuroendocrine carcinoma of the prostate (SCNECP) is a rare, aggressive subtype of prostate carcinoma. Most SCNECP arise from conventional prostate adenocarcinoma (CPAC) treated with androgen deprivation therapy (ADT).

CASE PRESENTATIONS

We identified four cases of CPAC treated with ADT, which evolved to SCNECP with liver metastasis. The average interval between the diagnosis of CPAC and SCNECP was 102 months (range: 12 to 168). Histologically, the tumors showed nests of cells with high nuclear:cytoplasmic ratios, granular chromatin, and frequent mitoses. All cases were synaptophysin, chromogranin, and AE1/AE3 positive, with a Ki-67 labeling index ≥70%. NKX3.1 was negative in all but one case and TTF-1 was positive in half. Weak ERG positivity by IHC was seen in one case which also demonstrated the TMPRSS2-ERG gene rearrangement; all other cases were negative for ERG by IHC. Serum prostate specific antigen (PSA) levels were normal to near-normal in all. The median interval between the diagnosis of SCNECP and death was 3.25 months (range: 0.75 to 26).

CONCLUSIONS

Our case series highlights the importance of considering a prostate primary, even in the setting of normal PSA levels and loss of prostate markers, when diagnosing neuroendocrine carcinoma in the liver. Further, we emphasize the significance of diagnosing SCNECP that metastasizes to the liver, as it portends a particularly dismal prognosis.

Histiocytic Sarcoma Arising From a Long Bone: Report of Two Cases

Histiocytic sarcoma is a rare, but aggressive malignant neoplasm of monocyte/macrophage lineage with a wide age distribution. Bone involvement is exceedingly rarer compared to the lymph node, skin, and soft tissue, and no long bone involvement has been reported in the English literature. We here report 2 cases of histiocytic sarcoma involving the long bone: one from the femur of a 77-year-old female, status post the placement of an intramedullary nail for subtrochanteric hip fracture; the other from the radius of a 3-year-old female with no significant medical history. Radiologic imaging showed highly destructive lesions in both cases with soft-tissue extension. Microscopy in both cases showed sheets of polygonal mononuclear cells with abundant eosinophilic cytoplasm, prominent nucleoli, and frequent mitosis. Hemophagocytosis were also identified. Immunohistochemistry showed that the lesional cells were strongly diffusely positive for CD68 and CD163. The first patient deteriorated rapidly, despite the aggressive treatment of amputation and chemotherapy. However, the second patient is disease free 36 months post the treatment of amputation only. We conclude that the long bone could be the primary site of histiocytic sarcoma. Its prognosis could be very variable and it is difficult to predict its behavior based on morphological evaluation only.

Hepatocellular adenoma(s) arising in nodular regenerative hyperplasia in a patient with systemic lupus erythematosus

Hepatocellular adenoma (HCA) is a rare benign tumor of the liver with low risk of malignant transformation. It is associated with oral contraceptives/anabolic steroid use, metabolic disease, and rarely, vascular abnormalities. We report an interesting case of HCA arising in a background of diffuse hepatic nodular regenerative hyperplasia (NRH) in a 40-year-old female patient with systemic lupus erythematosus (SLE). She presented with sudden-onset refractory ascites, elevated liver enzymes, diffuse hepatic nodularity and mass lesions on imaging concerning for malignancy. Targeted biopsies of the mass lesion were performed with inconclusive diagnoses. The patient ultimately underwent resection of the mass, which was confirmed as HCA, inflammatory type, arising in a background of NRH. It is not uncommon for SLE patients to have liver manifestations such as NRH, but HCA arising in NRH has not been previously reported. Our case reveals an unusual relationship between HCA and hepatic vasculopathy in the clinical context of a systemic inflammatory condition, the mechanism by which is not fully understood.

Primary Dedifferentiated Amelanotic Anorectal Melanoma: Report of a Rare Case

Anorectal melanoma (ARM) is an uncommon aggressive malignancy that comprises 0.5% to 1.6% of all melanoma manifestations. Dedifferentiated melanoma is very rare with loss of all melanocytic differentiation markers and is usually seen in metastatic melanoma of cutaneous origin. In this article, we report the first case of primary dedifferentiated amelanotic ARM in a 68-year-old male who presented with anal discomfort that was initially treated as inflamed hemorrhoids. Physical examination revealed a large protruding anal mass, biopsy of which showed biphasic malignant tumor cells with distinct immunoprofiles: a superficial spindled/sarcomatoid component positive for SOX10 and S100, and a deeper epithelioid/rhabdoid component positive for desmin, AE1/AE3, and EMA. Both components were negative for HMB-45, Melan-A/MART-1, c-Kit, and other lineage markers. Molecular analysis by polymerase chain reaction demonstrated wild-type BRAF and KRAS genes. A diagnosis of dedifferentiated ARM was made based on the coexistence of a differentiated component (spindled: S100 and SOX10 positive) and a dedifferentiated component (epithelioid: all melanoma markers including S100 and SOX10 negative). Shortly afterwards, the patient developed extensive pulmonary and liver metastases and expired 20 days after the diagnosis was rendered, reinforcing the highly aggressive nature of this disease entity.

Unraveling the relationship between macula densa cell volume and luminal solute concentration/osmolality

At the macula densa, flow-dependent changes in luminal composition lead to tubuloglomerular feedback and renin release. Apical entry of sodium chloride in both macula densa and cortical thick ascending limb (cTAL) cells occurs via furosemide-sensitive sodium-chloride-potassium cotransport. In macula densa, apical entry of sodium chloride leads to changes in cell volume, although there are conflicting data regarding the directional change in macula densa cell volume with increases in luminal sodium chloride concentration. To further assess volume changes in macula densa cells, cTAL-glomerular preparations were isolated and perfused from rabbits, and macula densa cells were loaded with fluorescent dyes calcein and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate. Cell volume was determined with wide-field and multiphoton fluorescence microscopy. Increases in luminal sodium chloride concentration from 0 to 80 mmol/l at constant osmolality led to cell swelling in macula densa and cTAL cells, an effect that was blocked by luminal application of furosemide. However, increases in luminal sodium chloride concentration from 0 to 80 mmol/l with concomitant increases in osmolality caused sustained decreases in macula densa cell volume but transient increases in cTAL cell volume. Increases in luminal osmolality with urea also resulted in macula densa cell shrinkage. These studies suggest that, under physiologically relevant conditions of concurrent increases in luminal sodium chloride concentration and osmolality, there is macula densa cell shrinkage, which may play a role in the macula densa cell signaling process.

Cellular mechanisms of WNK4-mediated regulation of ion transport proteins in the distal tubule

Gene mutations in WNK4 kinase cause a genetic form of hypertension by affecting multiple ion transport pathways through different mechanisms. Cai et al. report that the inhibitory effect of WNK4 on the thiazide-sensitive sodium-chloride cotransporter occurs through the lysosomal degradation pathway in mammalian cells.

Current mechanisms of macula densa cell signalling

Macula densa cells couple renal haemodynamics, glomerular filtration and renin release with tubular fluid salt and water reabsorption. These cells detect changes in tubular fluid composition through a complex of intracellular signalling events that are mediated by membrane transport pathways. Increases in luminal fluid sodium chloride concentration result in alterations in cell sodium chloride concentration, cytosolic calcium, cell pH, basolateral membrane depolarization and cell volume. Macula densa signalling then involves the production and release of specific paracrine signalling molecules at their basolateral membrane. Upon moderate increases in luminal sodium chloride concentration macula densa cells release increasing amounts of ATP and decreasing amounts of prostaglandin E(2), thereby increasing afferent arteriolar tone and decreasing the release of renin from granular cells. On the other hand, further increases in luminal concentration stimulate the release of nitric oxide, which serve to prevent excessive tubuloglomerular feedback vasoconstriction. Paracrine signalling by the macula densa cells therefore controls juxtaglomerular function, renal vascular resistance and participates in the regulation of renin release.

Regulation of mesangial cell Na+/Ca2+ exchanger isoforms

An isoform of the Na(+)/Ca(2+) exchanger (SDNCX1.10) was cloned from mesangial cells of Sprague-Dawley rat. Regulation of this isoform was compared to two other clones that were derived from the Dahl/Rapp salt sensitive (SNCX) and salt resistant rat (RNCX). All isoforms differ at the alternative splice site and at amino acid 218 for SNCX. PKC activates RNCX but not SNCX while SDNCX1.10 was also activated by PKC. Regulation of exchanger activities by intracellular calcium ([Ca(2+)](i)), pH, and kinases was assessed using Na-dependent (45)Ca(2+) uptake assays in OK-PTH cells expressing the vector, RNCX, SNCX, or SDNCX1.10. [Ca(2+)](i) was elevated from 50 to 125 nM (n = 4) with thapsigargin (40 nM) and reduced from 50 to 29 nM (n = 4) and 18 nM (n = 4) with 10 or 20 microM BAPTA, respectively. RNCX was active at all three [Ca(2+)](i) while SNCX and SDNCX1.10 were only active at lower [Ca(2+)](i). Varying extracellular pH (pH(e), without nigericin) or pH(e) and intracellular pH (pH(i), with 10 microM nigericin) from pH 7.4 to 6.2, 6.8, or 8.0 showed that SNCX activity was attenuated at both low and high pHs. SDNCX1.10 activity was attenuated only at pH 6.2 and 6.8 (with or without nigericin) while RNCX activity was attenuated at pH 6.2 (with or without nigericin) and pH 6.8 (with nigericin). Finally, only SDNCX1.10 activity was stimulated by 250 microM CPT-cAMP or 250 microM DB-cGMP treatment. Thus the differential regulation of [Ca(2+)](i) by these exchangers is dependent upon the pattern of cellular Na(+)/Ca(2+) exchanger isoform expression.

Impaired ability of the Na+/Ca2+ exchanger from the Dahl/Rapp salt-sensitive rat to regulate cytosolic calcium

We previously cloned Na(+)/Ca(2+) exchanger (NCX1) from mesangial cells of salt-sensitive (SNCX = NCX1.7) and salt-resistant (RNCX = NCX1.3) Dahl/Rapp rats. The abilities of these isoforms to regulate cytosolic Ca(2+) concentration ([Ca(2+)](i)) were assessed in fura 2-loaded OK cells expressing the vector (VOK), RNCX (ROK), and SNCX (SOK). Baseline [Ca(2+)](i) was 98 +/- 20 nM (n = 12) in VOK and was significantly lower in ROK (44 +/- 5 nM; n = 12) and SOK (47 +/- 13 nM; n = 12) cells. ATP at 100 microM increased [Ca(2+)](i) by 189 +/- 55 nM (n = 12), 21 +/- 9 nM (n = 12), and 69 +/- 18 nM (n = 12) in VOK, ROK, and SOK cells, respectively. ATP (1 mM) or bradykinin (0.1 mM) caused large increases in [Ca(2+)](i) and ROK but not SOK cells were much more efficient in reducing [Ca(2+)](i) back to baseline levels. Parental Sprague-Dawley rat mesangial cells express both RNCX (SDRNCX) and SNCX (SDSNCX). SDRNCX and RNCX are identical at every amino acid residue, but SDSNCX and SNCX differ at amino acid 218 where it is isoleucine in SDSNCX and not phenylalanine. OK cells expressing SDSNCX (SDSOK) reduced ATP (1 mM)-induced [Ca(2+)](i) increase back to baseline at a rate equivalent to that for ROK cells. PKC downregulation significantly attenuated the rate at which ROK and SDSOK cells reduced ATP-induced [Ca(2+)](i) increase but had no effect in SOK cells. The reduced efficiency of SNCX to regulate [Ca(2+)](i) is attributed, in part, to the isoleucine-to-phenylalanine mutation at amino acid 218.

Equity in the diagnosis of chest pain: race and gender

OBJECTIVE

To explore gender and racial equity in emergency room treatment of chest pain.

METHODS

Three hundred seventy-nine patient records were analyzed, taking into account effects of age, clinic, comorbid status, and insurance status.

RESULTS

Analysis of covariance and logistic regression revealed statistically significant differences between races but not between genders for time to first EKG and percent of patients receiving cardiac catheterization and echocardiography. Blacks waited longer than whites for an EKG and were less likely to receive cardiac catheterizations but more likely to receive echocardiography.

CONCLUSION

This study demonstrates a lack of equity by race in treatment of chest pain emergencies.

Standards and the integrated electronic health care record

The goal of creating an integrated electronic health care record is within our reach. It will depend chiefly on the creation and adoption of standards for health care data. This article explains why standards development is important, gives examples of the different types of standards relevant to health care, offers examples of data sets used in health care, and, finally, presents examples of standards development organizations that health care supervisors should be familiar with.

Cloning of mesangial cell Na(+)/Ca(2+) exchangers from Dahl/Rapp salt-sensitive/resistant rats

The Dahl/Rapp rat model of hypertension is characterized by a marked increase in blood pressure and a progressive fall in glomerular filtration rate when salt-sensitive (S) rats are placed on an 8% NaCl diet. On the same diet, the salt-resistant (R) rat does not exhibit these changes. In previous studies we found that protein kinase C (PKC) upregulates Na(+)/Ca(2+) exchanger activity in afferent arterioles and mesangial cells from R but not S rats. One possible reason for the difference in PKC sensitivity may be due to differences in the S and R Na(+)/Ca(2+) exchanger protein. We now report the cloning of Na(+)/Ca(2+) exchangers from R (RNCX1) and S (SNCX1) mesangial cells. At the amino acid level, SNCX1 differs from RNCX1 at position 218 in the NH(2)-terminal domain where it is isoleucine in RNCX1 but phenylalanine in SNCX1. These two exchangers also differ by 23 amino acids at the alternative splice site within the cytosolic domain. RNCX1 and SNCX1 were expressed in OK-PTH cells and (45)Ca(2+)-uptake studies were performed. Acute phorbol 12-myristate 13-acetate (PMA) treatment (300 nM, 20 min) upregulated exchanger activity in cells expressing RNCX1 but failed to stimulate exchanger activity in SNCX1 expressing cells. Upregulation of RNCX1 could be prevented by prior 24-h pretreatment with PMA, which downregulates PKC. These results demonstrate a difference in PKC-Na(+)/Ca(2+) exchange activity between the isoform of the exchanger cloned from the R vs. the S rat. Lack of PKC activation of SNCX1 may contribute to a dysregulation of intracellular Ca(2+) concentration and enhanced renal vasoreactivity in this model of hypertension.

Macula densa Na(+)/H(+) exchange activities mediated by apical NHE2 and basolateral NHE4 isoforms

Functional and immunohistochemical studies were performed to localize and identify Na(+)/H(+) exchanger (NHE) isoforms in macula densa cells. By using the isolated perfused thick ascending limb with attached glomerulus preparation dissected from rabbit kidney, intracellular pH (pH(i)) was measured with fluorescence microscopy by using 2',7'-bis-(2-carboxyethyl)-5-(and -6) carboxyfluorescein. NHE activity was assayed by measuring the initial rate of Na(+)-dependent pH(i) recovery from an acid load imposed by prior lumen and bath Na(+) removal. Removal of Na(+) from the bath resulted in a significant, DIDS-insensitive, ethylisopropyl amiloride (EIPA)-inhibitable decrease in pH(i). This basolateral transporter showed very low affinity for EIPA and Hoechst 694 (IC(50) = 9.0 and 247 microM, respectively, consistent with NHE4). The recently reported apical NHE was more sensitive to inhibition by these drugs (IC(50) = 0.86 and 7.6 microM, respectively, consistent with NHE2). Increasing osmolality, a known activator of NHE4, greatly stimulated basolateral NHE. Immunohistochemical studies using antibodies against NHE1-4 peptides demonstrated expression of NHE2 along the apical and NHE4 along the basolateral, membrane, whereas NHE1 and NHE3 were not detected. These results suggest that macula densa cells functionally and immunologically express NHE2 at the apical membrane and NHE4 at the basolateral membrane. These two isoforms likely participate in Na(+) transport, pH(i), and cell volume regulation and may be involved in tubuloglomerular feedback signaling by these cells.

Renal sodium/calcium exchange; a vasodilator that is defective in salt-sensitive hypertension

The Na+ : Ca2+ exchanger is an important plasma membrane ion transport pathway that plays a major role in controlling [Ca2+]i. In smooth muscle cells, it may function as a Ca2+ extrusion pathway and may help lower [Ca2+]i in response to vasoconstrictor-induced increases in [Ca2+]i. It may also extrude [Ca2+]i and lead to vasodilation in response to vasodilators. Our recent studies have been performed to determine the existence and regulation of the Na+ : Ca2+ exchanger in renal contractile cells which include afferent and efferent arterioles and mesangial cells. Exchanger activity is present in all three of these contractile elements but is higher in afferent arterioles vs. efferent arterioles. We have also examined the role of altered regulation of the exchanger in the SHR and in salt-sensitive hypertension. With the establishment of high blood pressure, Na+ : Ca2+ exchanger activity is reduced in afferent but not in efferent arterioles in both models of hypertension. Other works in cultured mesangial cells and freshly dissected afferent arterioles, have shown that protein kinase C (PKC) up-regulates the Na+ : Ca2+ exchanger from Dahl/Rapp salt-resistant rats while it fails to do so in arterioles and mesangial cells from salt-sensitive rats. This defect in PKC regulation of Na+ : Ca2+ exchange is the result of a loss of PKC-mediated translocation of the exchanger to the plasma membrane in S mesangial cells. Thus, a defect in the PKC-Na+ : Ca2+ exchanger-translocation pathway may cause dysregulation of [Ca2+]i and help explain the dramatic decrease in GFR that occurs in this model of hypertension.

Cytosolic [Ca2+] signaling pathway in macula densa cells

Previous micropuncture studies suggested that macula densa (MD) cells might detect variations in luminal sodium chloride concentration ([NaCl]l) through changes in cytosolic calcium ([Ca2+]c). To test this hypothesis, MD [Ca2+]c was measured with fluorescence microscopy using fura 2 in the isolated perfused thick ascending limb with attached glomerulus preparation dissected from rabbit kidney. Tubules were bathed and perfused with a Ringer solution, [NaCl]l was varied and isosmotically replaced with N-methyl-D-glucamine cyclamate. Control [Ca2+]c, during perfusion with 25 mM NaCl and 150 mM NaCl in the bath, averaged 101. 6 +/- 8.2 nM (n = 21). Increasing [NaCl]l to 150 mM elevated [Ca2+]c by 39.1 +/- 5.2 nM (n = 21, P < 0.01). This effect was concentration dependent between zero and 60 mM [NaCl]l. The presence of either luminal furosemide or basolateral nifedipine or 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), a potent Cl- channel blocker, significantly reduced resting [Ca2+]c and abolished the increase in [Ca2+]c in response to increased [NaCl]l. Nifedipine failed to produce a similar inhibitory effect when added exclusively to the luminal perfusate. Also, 100 nM BAY K 8644, a voltage-gated Ca2+ channel agonist, added to the bathing solution increased [Ca2+]c by 33.2 +/- 8.1 nM (n = 5, P < 0.05). These observations suggest that MD cells may detect variations in [NaCl]l through a signaling pathway that includes Na+-2Cl--K+ cotransport, basolateral membrane depolarization via Cl- channels, and Ca2+ entry through voltage-gated Ca2+ channels.

Altered protein kinase C activation of Na+/Ca2+ exchange in mesangial cells from salt-sensitive rats

The purpose of these studies was to determine whether there is a defect in protein kinase C (PKC) regulation of the Na+/Ca2+ exchanger in cultured mesangial cells (MC) from Dahl/Rapp salt-sensitive (S) and salt-resistant (R) rats. R and S MCs were cultured, grown on coverslips, and loaded with fura 2 for measurement of single cell cytosolic calcium concentration ([Ca2+]i) in a microscope-based photometry system. Studies were performed in cells that were exposed to serum (serum fed) and in cells that were serum deprived for 24 h. Baseline [Ca2+]i values measured in a Ringer solution containing 150 mM NaCl were similar between R and S MCs in both serum-fed and serum-deprived groups, although baseline [Ca2+]i values were uniformly higher in the serum-deprived groups. Exchanger activity was assessed by reducing extracellular Na (Nae) from 150 to 2 mM, which resulted in movement of Na+ out of and Ca2+ into these cells (reverse-mode Na+/Ca2+ exchange). PKC was activated in these cells with 15-min exposure to 100 nM phorbol 12-myristate 13-acetate (PMA). In the absence of PMA, the change in [Ca2+]i (Delta[Ca2+]i) with reduction in Nae was similar between R and S MCs in both serum-fed and serum-deprived groups, although the magnitude of Delta[Ca2+]i was enhanced by serum deprivation. In both serum-fed and serum-deprived groups, PMA significantly increased Delta[Ca2+]i in R but not S MCs. Upregulation of exchanger activity in R MCs could be abolished by prior 24-h exposure to PMA, a maneuver that downregulates PKC activity. Other studies were performed to evaluate exchanger protein expression using monoclonal and polyclonal antibodies. Immunoblots of PMA-treated cells revealed an increase in the levels of 70- and 120-kDa proteins in the crude membrane fraction of R but not S MCs, an increase which was abrogated by prior 24-h PMA pretreatment and corresponded to reduction in the 70-kDa protein in the crude cytosolic fraction. These data demonstrate that PKC enhances Na+/Ca2+ exchange activity in MCs from R but not from S rats, suggesting that there may be a defect in the PKC-Na+/Ca2+ exchange regulation pathway in MCs of S rats.

Renal arteriolar Na+/Ca2+ exchange in salt-sensitive hypertension

The present studies were performed to assess Na+/Ca2+ exchange activity in afferent and efferent arterioles from Dahl/Rapp salt-resistant (R) and salt-sensitive (S) rats. Renal arterioles were obtained by microdissection from S and R rats on either a low-salt (0.3% NaCl) or high-salt (8.0% NaCl) diet. On the high-salt diet, S rats become markedly hypertensive. Cytosolic calcium concentration ([Ca2+]i) was measured in fura 2-loaded arterioles bathed in a Ringer solution in which extracellular Na (Nae) was varied from 150 to 2 mM (Na was replaced with N-methyl-D-glucamine). Baseline [Ca2+]i was similar in afferent arterioles of R and S rats fed low- and high-salt diet. The change in [Ca2+]i (Delta[Ca2+]i) during reduction in Nae from 150 to 2 mM was 80 +/- 10 and 61 +/- 3 nM (not significant) in afferent arterioles from R rats fed the low- and high-salt diet, respectively. In afferent arterioles from S rats on a high-salt diet, Delta[Ca2+]i during reductions in Nae from 150 to 2 mM was attenuated (39 +/- 4 nM) relative to the Delta[Ca2+]i of 79 +/- 13 nM (P < 0.05) obtained in afferent arterioles from S rats on a low-salt diet. In efferent arterioles, baseline [Ca2+]i was similar in R and S rats fed low- and high-salt diets, and Delta[Ca2+]i in response to reduction in Nae was also not different in efferent arterioles from R and S rats fed low- or high-salt diets. Differences in regulation of the exchanger in afferent arterioles of S and R rats were assessed by determining the effects of protein kinase C (PKC) activation by phorbol 12-myristate 13-acetate (PMA, 100 nM) on Delta[Ca2+]i in response to reductions in Nae from 150 to 2 mM. PMA increased Delta[Ca2+]i in afferent arterioles from R rats but not from S rats. These results suggest that Na+/Ca2+ exchange activity is suppressed in afferent arterioles of S rats that are on a high-salt diet. In addition, there appears to be a defect in the PKC-Na+/Ca2+ exchange pathway that might contribute to altered [Ca2+]i regulation in this important renal vascular segment in salt-sensitive hypertension.

Angiotensin II stimulates macula densa basolateral sodium/hydrogen exchange via type 1 angiotensin II receptors

Angiotensin II (AngII) enhances tubuloglomerular feedback responses and is considered to be a specific modulator of feedback activity. The sites at which AngII interacts with the signal transmission process remain unknown. In certain renal epithelia, AngII stimulates Na/H exchange activities. Evidence for the regulation of macula densa apical Na/H exchange by AngII was recently reported. Because macula densa cells also express a basolateral Na/H exchanger, the possibility that AngII stimulates this exchanger activity was investigated. In preparations of isolated perfused thick ascending limb with attached glomerulus dissected from rabbit kidney, the intracellular pH (pHi) of macula densa cells was measured with fluorescence microscopy using 2',7'-bis(2-carboxyethyl)-5-(and -6)carboxyfluorescein. Perfusion and bathing solutions were iso-osmotic Cl-free Ringer's solutions modified using N-methyl-D-glucamine and cyclamate as the Na and Cl substitutes, respectively. Control pHi, during perfusion with 0 mM Na and 150 mM Na in the bath, averaged 7.21+/-0.07 (n=10). Removal of Na from the bath (i.e., basolateral solution) decreased pHi by 0.39+/-0.06 units (n=5, P < 0.01). Addition of 10(-9) M AngII to the bath resulted in a significant increase in the Na-dependent acid load. This increase in Na-dependent cell acidification was completely blocked by coadministration of the AngII type 1 (AT1) receptor blocker candesartan (10(-8) M). In addition, AngII increased the rate of pHi recovery from the acid load induced by readdition of bath Na. This stimulatory effect of AngII was also completely reversed by coadministration of the AT1 receptor blocker candesartan. These results indicate that AngII stimulates macula densa basolateral Na/H exchange via AT1 receptors and therefore may affect tubuloglomerular feedback signal transmission, at least in part, through direct effects on macula densa transport processes.

Regulation of macula densa Na:H exchange by angiotensin II

BACKGROUND

Angiotensin II (Ang II) is a positive modulator of tubuloglomerular feedback (TGF). At the present time, the site(s) at which Ang II interacts with the signal transmission process remains unknown. In certain renal epithelia, Ang II is known to stimulate apical Na:H exchange. Since macula densa cells possess an apical Na:H exchanger and Ang II subtype I receptors (AT1-receptors), we tested the possibility that Ang II might stimulate exchanger activity in these cells.

METHODS

Using the isolated perfused thick ascending limb with attached glomerulus preparation dissected from rabbit kidney, macula densa intracellular pH (pHi) was measured with fluorescence microscopy using BCECF.

RESULTS

Control pHi, during perfusion with 25 mM NaCl and 150 mM NaCl in the bath, averaged 7.22 +/- 0.02 (N = 24). Increasing luminal [NaCl] to 150 mM elevated pHi by 0.54 +/- 0.04 (N = 7, P < 0.01). Ang II (10(-9) M), added to the bath in the same paired experiments, significantly elevated baseline pHi by 0.17 +/- 0.04, increased the magnitude of change in pHi (delta = 0.71 +/- 0.05) and initial rate of alkalinization (by 69%) to increased luminal [NaCl]. Ang II produced similar effects when added exclusively to the luminal perfusate. In addition, low-dose Ang II (10(-9) M) stimulated while high-dose Ang II (10(-6) M) inhibited Na-dependent pH-recovery from an acid load. AT1 blockade prevented the stimulatory but not the inhibitory effects of Ang II.

CONCLUSION

Through the AT1, Ang II may influence macula densa Na transport and regulate cell alkalinization via the apical Na:H exchanger. Thus, Ang II may modulate the TGF signal transmission process, at least in part, through a direct effect on macula densa cell function.

Transport and regulatory properties of the apical Na-K-2Cl cotransporter of macula densa cells

NH+4/NH3 fluxes were used to probe apical Na-K-2Cl transport activity of macula densa (MD) cells from rabbit kidney. In the presence of 25 mM NaCl and 5 mM Ba2+, addition of 20 mM NH+4 to the lumen produced a profound intracellular acidification, and approximately 80% of the initial acidification rate was bumetanide sensitive. The NH+4-induced acidification rate was dependent on luminal Cl- and Na+ with apparent affinities of 17 +/- 4 mM (Hill number 1.45) and 1.0 +/- 0.3 mM, respectively. In the presence of saturating luminal NaCl concentration ([NaCl]L), blockade of basolateral Cl- efflux with 10 microM 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) reduced the NH+4-induced acidification rate by 51 +/- 6% (P > 0.01, n = 5). Under similar conditions, dibutyryl-cAMP (DBcAMP) + forskolin increased the NH+4-induced acidification rate by 27%, whereas it produced no detectable effect at low luminal NaCl concentration. Most of the observed DBcAMP + forskolin effect was probably due to the stimulation of the basolateral Cl- conductance, since, in the presence of basolateral NPPB, this activation was changed to a 17.1% and 16.6% inhibition of the NH+4-induced acidification rate observed at high or low [NaCl]L, respectively. We conclude that the cotransporter found in MD cells displays, with respect to other Na-K-2Cl cotransporters, a relatively high affinity for luminal Na+ and luminal Cl- and can be specifically inhibited by increases in intracellular Cl- and cAMP concentrations.

Ionic transport in macula densa cells

Recent work has provided substantial insights into functional characteristics of macula densa (MD) cells. Microelectrode and patch-clamp experiments on the rabbit isolated thick ascending limb (TAL)/glomerulus preparation have shown that MD cells possess a furosemide-sensitive Na:K:2Cl cotransporter, an apical 41-pS K+ channel, and a dominant basolateral Cl- conductance. Increasing luminal fluid [NaCl] ([NaCl]L) results in furosemide-sensitive cell depolarization due to a rise in intracellular [Cl-] that stimulates basolateral electrogenic Cl- efflux. Intracellular pH (pHi) measurements show the presence of an apical Na:H exchanger that couples transepithelial Na+ transport to pHi. Experimental results and thermodynamic considerations allow estimation of intracellular [Na+] and [Cl-] ([Na+]i, [Cl-]i) under different conditions. When the Na:K:2Cl cotransporter is equilibrated (or in the presence of furosemide), [Na+]i and [Cl-]i are low (approximately 6 to 7 mM), whereas when the cotransporter is fully activated, [Na+]i and [Cl-]i increase substantially to approximately 70 and 20 mM, respectively. Finally, luminal addition of NH4+ produces cell acidification that depends on NH4+ apical transport rate through the Na:K:2Cl. Using a simple transport model for NH4+, the initial NH4+ influx rate in MD cells is comparable to the corresponding flux in TAL. This challenges the idea that MD cells have a low transport activity but supports our findings about large changes in intracellular concentrations as a function of [NaCl]L.

Characteristics of membrane transport processes of macula densa cells

1. Macula densa (MD) cells are located within the thick ascending limb (TAL) and have their apical surface in contact with tubular fluid and their basilar region in contact with the glomerulus. These cells sense changes in luminal fluid sodium chloride concentration ([NaCl]) and transmit signals resulting in changes in vascular resistance (tubuloglomerular feedback) and renin release. 2. Current efforts have focused on understanding the cellular transport mechanisms of MD cells. Progress in this area has benefited from the use of the isolated perfused TAL-glomerular preparation, which permits direct access to MD cells. 3. Using microelectrodes to measure basolateral membrane potential (VBL) of MD cells, it was found that VBL was very sensitive to changes in luminal fluid [NaCl]. As [NaCl] was elevated from 20 to 150 mmol/L, VBL was found to depolarize by over 30 mV. 4. Basolateral membrane potential measurements were also used to identify an apical Na+:2Cl-:K+ cotransport pathway in MD cells that is the major pathway for NaCl entry into these cells. 5. Other work identified a basolateral chloride channel that is presumed to be responsible for changes in VBL during alterations in luminal [NaCl]. This channel, which is the predominant conductance across the basolateral membrane, may be regulated by intracellular Ca2+ and cAMP. 6. An apical Na+:H+ exchanger in MD cells was detected by measuring changes in intracellular pH using the fluorescent probe 2',7'-bis-(2-carboxyethyl)-5(and-6) carboxyfluorescein. 7. Using patch-clamp techniques, a high density of pH- and Ca(2+)-sensitive K+ channels was observed at the apical membrane of MD cells. 8. Other studies found that, at the normal physiological conditions prevailing at the end of the TAL (luminal [NaCl] of 20-60 mmol/L), reabsorption mediated by MD cells is very sensitive to changes in luminal [NaCl].

Oxidation inhibits substrate proteolysis by calpain I but not autolysis

In this study, the effects of oxidation on calpain I autolysis and calpain-mediated proteolysis were examined. Calpain I was incubated with increasing concentrations of free calcium in the presence or absence of oxidant, and autolytic conversion of both the 80- and 30-kDa subunits was measured by immunoblotting utilizing monoclonal antibodies which recognize both autolyzed and non-autolyzed forms of each subunit, respectively. Autolytic conversion of the 80-kDa subunit of calpain I was not detected until free calcium concentration was greater than 40 microM, whereas autolysis of the 30-kDa subunit did not occur until the free calcium concentration was greater than 100 microM. In addition, autolytic conversion of either the 80- or 30-kDa subunit was not inhibited by the presence of oxidant. Calpain I activity was measured using the fluorescent peptide N-succinyl-L-leucyl-L-leucyl-L-valyl-L-tyrosine-7-amido-4- methylcoumarin or the microtubule-associated protein tau as substrate. Calpain I was found to have proteolytic activity at free calcium concentrations below that required for autolysis. Calpain I activity was strongly inhibited by oxidant at all calcium concentrations studied, suggesting that proteolytic activity of both the non-autolyzed 80-kDa and autolyzed 76-kDa forms was susceptible to oxidation. Interestingly, whereas oxidation did not inhibit autolytic conversion, the presence of high substrate concentrations did result in a significant reduction of autolysis without altering calpain proteolytic activity. Calpain I activity that had been inhibited by the presence of oxidant was recovered immediately by addition of the reducing agent dithiothreitol.

Characterization of sodium-calcium exchange in rabbit renal arterioles

Experiments were performed to test the hypothesis that renal arterioles exhibit Na-Ca exchange capability and that this process is regulated by protein kinase C (PKC). Glomeruli with attached arterioles were dissected from rabbit kidney and loaded with fura-2 for measurement of intracellular calcium concentration ([Ca2+]i) using microscope-based photometry. In tissue bathed in Ringer's solution containing 150 mM Na+ and 1.5 mM Ca2+, afferent and efferent arteriolar [Ca2+]i averaged 136 +/- 6 and 154 +/- 7 nM, respectively. Removal of extracellular Na+ increased afferent arteriolar [Ca2+]i by 70 +/- 7 mM, while efferent arteriolar [Ca2+]i only increased by 39 +/- 5 nM (P < 0.01 vs. afferent arteriole). These responses were inhibited by 6 nM Ni2+ and required extracellular Ca2+, but were unaffected by 10 microM diltiazem. After incubation in 500 microM ouabain, 5 microM monensin, and 5 microM nigericin, [Ca2+]i responses to removal of extracellular Na+ were exaggerated significantly, averaging 174 +/- 50 nM in afferent arterioles and 222 +/- 82 nM in efferent arterioles (NS vs. afferent arterioles). Moreover, responses to removal of extracellular Na+ were enhanced by 100 nM phorbol 12-myristate 13-acetate, an affect which was blocked by PKC inhibition (25 nM K252b). These data indicate that both afferent and efferent arterioles express the Na-Ca exchanger, and that PKC activity impacts on exchange capacity in these vessels.

Altered sodium-calcium exchange in afferent arterioles of the spontaneously hypertensive rat

Studies were performed to determine if there is a derangement in Na-Ca exchange activity in afferent (AA) and efferent (EA) arterioles from 3- and 9-week-old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Cytosolic calcium concentration ([Ca2+]i) was assessed using microscope-based photometry in fura-2 loaded arterioles bathed in a Ringer's solution. Baseline [Ca2+]i was similar in the AA of 3- and 9-week-old WKY and SHR. In AA from 3-week-old rats, [Ca2+]i increased by 89 +/- 15 nM in WKY and by 73 +/- 13 nM in SHR during decreases in bath sodium concentration ([Na+]e) from 150 to 2 mM (Na+ replaced with n-methyl-D-glucamine). In 9-week-old hypertensive SHR (SBP = 150 mm Hg), increases in [Ca2+]i were attenuated (24 +/- 3 nM) relative to 3-week-old WKY and SHR, and 9-week-old WKY (90 +/- 9 nM; P < 0.05). Likewise, the rate of removal of Ca2+ in the continued presence of 2 mM Nae (Ca2+ sequestration and/or extrusion) was markedly reduced in AA of 9-week-old SHR (-0.15 +/- 0.03 nM/second) versus 3-week-old SHR (-0.72 +/- 0.12 nM/second) and 3- and 9-week-old WKY (-0.49 +/- 0.10 and -0.67 +/- 0.14 nM/second). In other experiments, AAs were preincubated in 1 mM ouabain to increase intracellular [Na+]. This maneuver augmented the increase in [Ca2+]i obtained with removal of Na+e; however, the responses obtained in 9-week-old SHR arterioles were still attenuated compared to those obtained in arterioles for 3- and 9-week-old WKY and 3-week-old SHR. These results suggest that exchanger number and/or sensitivity to the transmembrane Na gradient was reduced in the SHR AA. In EA, baseline [Ca2+]i was similar in 3- and 9-week-old WKY and SHR. In contrast to AA, the magnitude of Na-dependent and Na-independent changes in [Ca2+]i was not different in the EA of 3- and 9-week-old WKY and SHR. These results indicate that regulation of Na-Ca exchange activity may differ between AA and EA segments. Furthermore, diminished Na-Ca exchange and Na-independent Ca2+ sequestering/extrusion mechanisms could contribute to altered AA [Ca2+]i in the SHR.

A non-radioactive fluorescent method for measuring protein kinase C activity

The purpose of this study is to report the development of a non-radioactive fluorescent peptide assay for measuring protein kinase C activity (PKC). The assay is based on a glycogen synthase derived fluorescent peptide that is phosphorylated by PKC. Phosphorylation causes the peptide to migrate toward the anode while the non-phosphorylated peptide migrates toward the cathode during agarose gel electrophoresis. Quantitation of PKC activity can be accomplished by excision of the appropriate bands and measuring their relative fluorescence. Using this assay, PKC activity was measured in whole cell homogenates from cultured renal mesangial cells. The enzyme(s)-substrate system followed Michaelis-Menten kinetics under limited conditions and, therefore, Lineweaver-Burk plots were used to obtain Michaelis constant and maximum velocity values. An apparent KM value of 40 microM was obtained for the fluorescent peptide substrate with a control Vmax value of 300 pmol/min. Addition of phorbol 12-myristate 13-acetate increased Vmax to 380 pmol/min.

Activation of Na:2Cl:K cotransport by luminal chloride in macula densa cells

Changes in macula densa intracellular pH (pHi) were used to monitor the direction of flux mediated by the apical Na:2Cl:K cotransporter. At the macula densa, a decrease in luminal [Cl] ([Cl]1) from 60 to 1 mM produced cellular alkalinization secondary to a cascade of events involving a decrease in apical Na:2Cl:K cotransport, a fall in intracellular [Na] ([Na]i) and a stimulation of Na:H exchange. This is supported by the fact that 97% of the change in macula densa pHi with reduction in [Cl]1 was bumetanide-sensitive whereas 92% of this pH change was amiloride-sensitive. We found that, in the presence of 20 mM Na and 5 mM K, a [Cl]1 of 14.3 +/- 2.4 mM (N = 7) produced equilibrium of the apical cotransporter since the pHi obtained under this condition was identical to the pHi found after reducing the net ionic flux to zero with bumetanide. Using this value together with the expected stoichiometry for the bumetanide-sensitive cotransporter, it was estimated that the intracellular [Cl] ([Cl]i) at equilibrium (or in the presence of bumetanide) could be as low as 5 mM. Also, using a Hill number of 2 which is consistent with the present data, the affinity for [Cl]1 was found to be 32.5 mM. Under physiological luminal conditions prevailing at the end of the thick ascending limb (approximately 3.5 mM K, and approximately 25 to 30 mM NaCl), macula densa cells are probably operating close to equilibrium while maintaining a small net reabsorption of Na/K and Cl. Since macula densa cells appear capable of reducing [Cl]i to very low levels, a reabsorptive flux should continue to occur until [NaCl]1 is reduced to 18 mM.

Evidence for apical sodium proton exchange in macula densa cells

These studies were performed to determine if changes in luminal sodium chloride concentration ([NaCl]) might alter macula densa intracellular pH. Isolated thick ascending limbs with attached glomeruli were bathed in a 150 mM NaCl Ringer's solution and perfused in vitro with a 25 mM NaCl solution; N-methyl-D-glucamine cyclamate was used to substitute for NaCl. Macula densa cells were loaded with BCECF and intracellular pH was monitored using a microscope based-dual excitation photometer system. Control intracellular pH for all experiments in which tubules were initially perfused with 25 mM NaCl averaged 7.22 +/- 0.06; N = 28. Increasing luminal [NaCl] from 25 to 150 mM elevated macula densa pH by 0.15 +/- 0.03 (N = 6; P < 0.05) while increasing just luminal [Na] from 25 to 150 mM alkalinized macula densa cells by 0.17 +/- 0.05 (N = 6; P < 0.05). In addition, there was a highly significant linear relationship between luminal [Na] and intracellular pH between 25 and 150 mM NaCl. Other studies were performed to assess the effects of amiloride, an inhibitor of Na:H exchange, on macula densa intracellular pH. Addition of amiloride, to the 25 mM NaCl perfusate acidified macula densa cells by 0.09 +/- 0.03 (N = 6; P < 0.001) and significantly attenuated the increase in pH obtained when luminal [NaCl] was raised from 25 to 150 mM. Other studies evaluated the effects of inhibition of Na:2Cl:K cotransport on macula densa pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Basic properties and potential regulators of the apical K+ channel in macula densa cells

These studies examine the properties of an apical potassium (K+) channel in macula densa cells, a specialized group of cells involved in tubuloglomerular feedback signal transmission. To this end, individual glomeruli with thick ascending limbs (TAL) and macula densa cells were dissected from rabbit kidney and the TAL covering macula densa cells was removed. Using patch clamp techniques, we found a high density (up to 54 channels per patch) of K+ channels in the apical membrane of macula densa cells. An inward conductance of 41.1 +/- 4.8 pS was obtained in cell-attached patches (patch pipette, 140 mM K+). In inside-out patches (patch pipette, 140 mM; bath, 5 mM K+), inward currents of 1.1 +/- 0.1 pA (n = 11) were observed at 0 mV and single channel current reversed at a pipette potential of -84 mV giving a permeability ratio (PK/PNa) of over 100. In cell-attached patches, mean channel open probability (N,Po, where N is number of channels in the patch and Po is single channel open probability) was unaffected by bumetanide, but was reduced from 11.3 +/- 2.7 to 1.6 +/- 1.3 (n = 5, p < 0.02) by removal of bath sodium (Na+). Simultaneous removal of bath Na+ and calcium (Ca2+) prevented the Na(+)-induced decrease in N.Po indicating that the effect of Na+ removal on N.Po was probably mediated by stimulation of Ca2+ entry. This interpretation was supported by studies where ionomycin, which directly increases intracellular Ca2+, produced a fall in N.Po from 17.8 +/- 4.0 to 5.9 +/- 4.1 (n = 7, p < 0.02). In inside-out patches, the apical K+ channel was not sensitive to ATP but was directly blocked by 2 mM Ca2+ and by lowering bath pH from 7.4 to 6.8. These studies constitute the first single channel observations on macula densa cells and establish some of the characteristics and regulators of this apical K+ channel. This channel is likely to be involved in macula densa transepithelial Cl- transport and perhaps in the tubuloglomerular feedback signaling process.

Segmentally distinct effects of depolarization on intracellular [Ca2+] in renal arterioles

Experiments were performed to determine the influence of depolarization on intracellular Ca2+ concentration ([Ca2+]i) in renal arterioles and the possible role of voltage-gated Ca2+ channels in these responses. Glomeruli with attached arterioles and thick ascending limb were dissected from rabbit kidney and loaded with fura 2. [Ca2+]i of nonperfused arterioles was monitored using a microscope-based dual-excitation wavelength spectrofluorometry system. Afferent arteriolar [Ca2+]i averaged 150 +/- 11 nM (n = 20) when bathed in Ringer solution containing 1.5 mM Ca2+ and 5 mM K+. Replacement of the normal Ringer solution with one containing 100 mM K+ significantly increased afferent arteriolar [Ca2+]i to 196 +/- 12 nM. This response was abolished in the absence of extracellular Ca2+. In the presence of 1 microM nifedipine, 100 mM K+ elicited a 10% decrease in afferent arteriolar [Ca2+]i (P < 0.05). Thus nifedipine reversed the afferent [Ca2+]i response to depolarization, implicating voltage-gated Ca2+ channels as the influx pathway. In contrast to the behavior of afferent arterioles, the 100 mM K+ solution reduced efferent arteriolar [Ca2+]i from 188 +/- 17 to 148 +/- 13 nM (n = 11, P < 0.01), an effect that was not influenced by nifedipine. These observations support a role for voltage-gated Ca2+ channels in eliciting depolarization-induced increases in afferent arteriolar [Ca2+]i while failing to provide evidence for operation of such a mechanism at efferent arteriolar sites.

Intracellular Ca2+ and PKC activation do not inhibit Na+ and water transport in rat CCD

Experiments examined the effects of elevation of intracellular calcium concentration ([Ca2+]i) or activation of protein kinase C (PKC) on Na+ and water transport in the rat cortical collecting duct (CCD). We measured the lumen-to-bath 22Na+ flux (J1-->b), transepithelial voltage (VT), and water permeability (Pf) in CCD from deoxycorticosterone (DOC)-treated rats. Ionomycin (0.5 and 1 microM) and thapsigargin (1 and 2 microM) were used to increase [Ca2+]i. Phorbol 12-myristate 13-acetate (PMA; 0.3 and 1 microM) and oleoyl-acetyl-glycerol (OAG; 100 microM) were used as activators of PKC. [Ca2+]i was measured in isolated perfused tubules using the fluorescent dye fura 2. When added to the bathing solution, 220 pM arginine vasopressin (AVP) failed to affect [Ca2+]i, whereas 1 microM ionomycin increased [Ca2+]i by 103 +/- 15% and 2 microM thapsigargin increased [Ca2+]i by 24 +/- 4%. In flux studies, neither ionomycin nor thapsigargin affected J1-->b or Pf, although ionomycin caused marked morphological changes. Ionomycin also failed to alter either parameter in tubules from non-DOC-treated rats. Neither 100 microM OAG nor 1 microM PMA affected J1-->b or Pf. OAG at 50 microM had no effect on VT or transepithelial resistance, indicating no inhibition of conductive Na+ transport. We conclude that increased [Ca2+]i and PKC activation do not affect J1--b or Pf in the rat CCD. These findings may account for the sustained increase in J1--b produced in the rat CCD by AVP.

Transfection of the CD20 cell surface molecule into ectopic cell types generates a Ca2+ conductance found constitutively in B lymphocytes

CD20 is a plasma membrane phosphoprotein expressed exclusively by B lymphocytes. mAb binding to CD20 alters cell cycle progression and differentiation, indicating that CD20 plays an essential role in B lymphocyte function. Whole-cell patch clamp and fluorescence microscopy measurements of plasma membrane ionic conductance and cytosolic-free Ca2+ activity, respectively, were used to directly examine CD20 function. Transfection of human T and mouse pre-B lymphoblastoid cell lines with CD20 cDNA and subsequent stable expression of CD20 specifically increased transmembrane Ca2+ conductance. Transfection of CD20 cDNA and subsequent expression of CD20 in nonlymphoid cells (human K562 erythroleukemia cells and mouse NIH-3T3 fibroblasts) also induced the expression of an identical transmembrane Ca2+ conductance. The binding of a CD20-specific mAb to CD20+ lymphoblastoid cells also enhanced the transmembrane Ca2+ conductance. The mAb-enhanced Ca2+ currents had the same conductance characteristics as the CD20-associated Ca2+ currents in CD20 cDNA-transfected cells. C20 is structurally similar to several ion channels; each CD20 monomer possesses four membrane spanning domains, and both the amino and carboxy termini reside within the cytoplasm. Biochemical cross-linking of cell-surface molecules with subsequent immunoprecipitation analysis of CD20 suggests that CD20 may be present as a multimeric oligomer within the membrane, as occurs with several known membrane channels. Taken together, these findings indicate that CD20 directly regulates transmembrane Ca2+ conductance in B lymphocytes, and suggest that multimeric complexes of CD20 may form Ca2+ conductive ion channels in the plasma membrane of B lymphoid cells.

Permeability of the macula densa basement membrane area to high molecular weight molecules

To investigate the permeability properties of the basement membrane beneath macula densa cells and between extraglomerular mesangial cells, thick ascending limbs with attached glomeruli were dissected from rabbit kidney and incubated in a Ringers solution containing either horseradish peroxidase (HRP) (1 mg/ml; molecular weight approximately 40,000) or native or cationic ferritin (both at 5 mg/ml molecular weight approximately 450,000) for 5 and 20 min at room temperature. Tubules were processed for electron microscopy. At both time points, HRP reaction product fully permeated the matrix material between extraglomerular mesangial cells, the basement membrane underneath the macula densa, and also was occasionally located in intercellular spaces and intracellular vesicles within macula densa cells. Similar results were obtained with native and cationic ferritin. In separate experiments, thick ascending limbs with attached glomeruli were perfused for 20 min at room temperature with a Ringer solution containing HRP (1 mg/ml). HRP was found in tubulovesicular bodies within the apical cytoplasm of macula densa cells again indicating that these cells exhibit endocytotic activity. However, HRP did not gain access to intercellular spaces indicating that the apical junctional complex was impermeable to HRP. These results demonstrate that the macula densa basement membrane and matrix material between extraglomerular mesangial cells is permeable to high molecular weight molecules and suggest unhindered diffusion of water and solutes within this area.

Basolateral ionic permeabilities of macula densa cells

It has recently been shown that membrane ionic transport pathways of macula densa cells can be measured using conventional microelectrodes. To determine if conductances could be identified at the basolateral membrane of macula densa cells, cortical thick ascending limbs (CTAL) with attached glomeruli were continuously perfused with a 25 mM NaCl bicarbonate-free Ringer solution. Individual basolateral Na+, Cl-, NaCl, and K+ concentrations were altered by isosmotic replacement with N-methyl-D-glucamine and/or cyclamate. Reduction in basolateral [Na+] from 150 to 25 mM hyperpolarized basolateral membrane potential (Vbl) by 9.9 +/- 1.3 mV (n = 10; all data are corrected for changes in liquid junction potential at bath electrode). A decrease in bath [Cl-] from 150 to 25 mM depolarized Vbl by 20 +/- 2.4 mV (n = 13), whereas decreases in bath [NaCl] from 150 to 25 mM depolarized Vbl by 29 +/- 6.8 mV (n = 5). In the presence of 150 mM NaCl bathing solution, a stepwise increase in [K+] from 5 to 15 mM (by replacement of 10 mM NaCl with 10 mM KCl) depolarized Vbl by 3.3 +/- 1.1 mV (n = 8). After correction for individual transepithelial diffusion potentials, Cl conductance averaged 59 +/- 19% of the total basolateral conductance, whereas K+ (23 +/- 8%) and Na+ (17 +/- 10%) contributed significantly less to the overall basolateral conductance. These results indicate that membrane potential of macula densa cells may be very sensitive to alterations in intracellular Cl- activity and suggest that apical transport of NaCl through a furosemide-sensitive Na(+)-K(+)-2Cl- transporter may affect membrane potential in macula densa cells via a change in intracellular Cl- activity.