Inhibition of the mitochondrial calcium uniporter prevents IL-13 and allergen-mediated airway epithelial apoptosis and loss of barrier function

Mitochondria are increasingly recognized as key mediators of acute cellular stress responses in asthma. However, the distinct roles of regulators of mitochondrial physiology on allergic asthma phenotypes are currently unknown. The mitochondrial Ca²⁺ uniporter (MCU) resides in the inner mitochondrial membrane and controls mitochondrial Ca²⁺ uptake into the mitochondrial matrix. To understand the function of MCU in models of allergic asthma, in vitro and in vivo studies were performed using models of functional deficiency or knockout of MCU. In primary human respiratory epithelial cells, MCU inhibition abrogated mitochondrial Ca²⁺ uptake and reactive oxygen species (ROS) production, preserved the mitochondrial membrane potential and protected from apoptosis in response to the pleiotropic Th2 cytokine IL-13. Consequently, epithelial barrier function was maintained with MCU inhibition. Similarly, the endothelial barrier was preserved in respiratory epithelium isolated from MCU-/- mice after exposure to IL-13. In the ovalbumin-model of allergic airway disease, MCU deficiency resulted in decreased apoptosis within the large airway epithelial cells. Concordantly, expression of the tight junction protein ZO-1 was preserved, indicative of maintenance of epithelial barrier function. These data implicate mitochondrial Ca²⁺ uptake through MCU as a key controller of epithelial cell viability in acute allergic asthma.

Mitochondrial CaMKII inhibition in airway epithelium protects against allergic asthma

Excessive ROS promote allergic asthma, a condition characterized by airway inflammation, eosinophilic inflammation, and increased airway hyperreactivity (AHR). The mechanisms by which airway ROS are increased and the relationship between increased airway ROS and disease phenotypes are incompletely defined. Mitochondria are an important source of cellular ROS production, and our group discovered that Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is present in mitochondria and activated by oxidation. Furthermore, mitochondrial-targeted antioxidant therapy reduced the severity of allergic asthma in a mouse model. Based on these findings, we developed a mouse model of CaMKII inhibition targeted to mitochondria in airway epithelium. We challenged these mice with OVA or Aspergillus fumigatus. Mitochondrial CaMKII inhibition abrogated AHR, inflammation, and eosinophilia following OVA and A. fumigatus challenge. Mitochondrial ROS were decreased after agonist stimulation in the presence of mitochondrial CaMKII inhibition. This correlated with blunted induction of NF-κB, the NLRP3 inflammasome, and eosinophilia in transgenic mice. These findings demonstrate a pivotal role for mitochondrial CaMKII in airway epithelium in mitochondrial ROS generation, eosinophilic inflammation, and AHR, providing insights into how mitochondrial ROS mediate features of allergic asthma.

CaMKII inhibition in type II pneumocytes protects from bleomycin-induced pulmonary fibrosis by preventing Ca2+-dependent apoptosis

The calcium and calmodulin-dependent kinase II (CaMKII) translates increases in intracellular Ca(2+) into downstream signaling events. Its function in pulmonary pathologies remains largely unknown. CaMKII is a well-known mediator of apoptosis and regulator of endoplasmic reticulum (ER) Ca(2+). ER stress and apoptosis of type II pneumocytes lead to aberrant tissue repair and progressive collagen deposition in pulmonary fibrosis. Thus we hypothesized that CaMKII inhibition alleviates fibrosis in response to bleomycin by attenuating apoptosis and ER stress of type II pneumocytes. We first established that CaMKII was strongly expressed in the distal respiratory epithelium, in particular in surfactant protein-C-positive type II pneumocytes, and activated after bleomycin instillation. We generated a novel transgenic model of inducible expression of the CaMKII inhibitor peptide AC3-I limited to type II pneumocytes (Tg SPC-AC3-I). Tg SPC-AC3-I mice were protected from development of pulmonary fibrosis after bleomycin exposure compared with wild-type mice. CaMKII inhibition also provided protection from apoptosis in type II pneumocytes in vitro and in vivo. Moreover, intracellular Ca(2+) levels and ER stress were increased by bleomycin and significantly blunted with CaMKII inhibition in vitro. These data demonstrate that CaMKII inhibition prevents type II pneumocyte apoptosis and development of pulmonary fibrosis in response to bleomycin. CaMKII inhibition may therefore be a promising approach to prevent or ameliorate the progression of pulmonary fibrosis.

NEDD4 ubiquitin ligase is a putative oncogene in endometrial cancer that activates IGF-1R/PI3K/Akt signaling

OBJECTIVE

The PI3K/Akt pathway is frequently dysregulated in endometrial cancer, the most common gynecologic malignancy. Emerging evidence identifies the ubiquitin ligase NEDD4 as a key regulator of the PI3K/Akt pathway via activation of insulin-like growth factor-1 receptor (IGF-1R). Our objective was to understand the role of NEDD4 in endometrial cancer.

METHODS

NEDD4 expression was assessed by immunohistochemistry in a tissue microarray with 77 endometrial lesions ranging from normal benign endometrium to tumor specimens of varying stage and grade. Studies were extended to a panel of eight endometrial cancer cell lines phenotypically representing the most common endometrial patient tumors.

RESULTS

Immunohistochemistry demonstrated robust staining of NEDD4 in endometrial tumor specimens, with greater NEDD4 expression in the most aggressive tumors. Expression of NEDD4 was detected in a majority of endometrial cancer cell lines surveyed. Exogenous overexpression of murine Nedd4 in endometrial cancer cell lines with modest endogenous NEDD4 expression resulted in a significant increase in the rate of proliferation. Nedd4 overexpression also promoted an increase in cell surface localization of IGF-1R and activation of Akt. Inhibition of PI3K/Akt signaling reversed the enhanced cell growth in Nedd4-overexpressing endometrial cancer cells. In addition, the expression of NEDD4 in endometrial tumors positively correlated with the Akt downstream effector FoxM1.

CONCLUSIONS

This study identifies NEDD4 as a putative oncogene in endometrial cancer that may augment activation of the IGF-1R/PI3K/Akt signaling pathway.

Mitochondrial-targeted antioxidant therapy decreases transforming growth factor-β-mediated collagen production in a murine asthma model

Asthma is a disease of acute and chronic inflammation in which cytokines play a critical role in orchestrating the allergic inflammatory response. IL-13 and transforming growth factor (TGF)-β promote fibrotic airway remodeling, a major contributor to disease severity. Improved understanding is needed, because current therapies are inadequate for suppressing development of airway fibrosis. IL-13 is known to stimulate respiratory epithelial cells to produce TGF-β, but the mechanism through which this occurs is unknown. Here, we tested the hypothesis that reactive oxygen species (ROS) are a critical signaling intermediary between IL-13 or allergen stimulation and TGF-β-dependent airway remodeling. We used cultured human bronchial epithelial cells and an in vivo mouse model of allergic asthma to map a pathway where allergens enhanced mitochondrial ROS, which is an essential upstream signal for TGF-β activation and enhanced collagen production and deposition in airway fibroblasts. We show that mitochondria in airway epithelium are an essential source of ROS that activate TGF-β expression and activity. TGF-β from airway epithelium stimulates collagen expression in fibroblasts, contributing to an early fibrotic response to allergen exposure in cultured human airway cells and in ovalbumin-challenged mice. Treatment with the mitochondrial-targeted antioxidant, (2-(2,2,6,6-Tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl)triphenylphosphonium chloride (mitoTEMPO), significantly attenuated mitochondrial ROS, TGF-β, and collagen deposition in OVA-challenged mice and in cultured human epithelial cells. Our findings suggest that mitochondria are a critical source of ROS for promoting TGF-β activity that contributes to airway remodeling in allergic asthma. Mitochondrial-targeted antioxidants may be a novel approach for future asthma therapies.

Chloride channels in basolateral TAL membranes. XVIII. Phenylglyoxal induces functional mcCIC-Ka activity in basolateral MTAL membranes

Cultured mouse MTAL cells contain more mRNA encoding the Cl- channel mcCIC-Ka, which mediates CTAL Cl- absorption, than mRNA encoding the Cl- channel mmCIC-Ka, which mediates MTAL Cl- absorption. mmCIC-Ka and mcCIC-Ka have three functional differences: 1) mmCIC-Ka open time probability, Po, increases with increasing cytosolic Cl-, but variations in cytosolic Cl- do not affect Po in mcCIC-Ka; 2) mmCIC-Ka is gated by (ATP + PKA), while (ATP + PKA) have no effect on Po in mcCIC-Ka; and 3) mmCIC-Ka channels have single-ion occupancy, while mcCIC-Ka channels have multi-ion occupancy. Using basolateral vesicles from MTAL cells fused into bilayers, we evaluated the effects of 1 mM cytosolic phenylglyoxal (PGO), which binds covalently to lysine or arginine, on Cl- channels. With PGO pretreatment, Cl- channels were uniformly not gated either with increases in cytosolic-face Cl- or with (ATP + PKA) at 2 mM cytosolic-face Cl-; and they exhibited multi-ion occupancy kinetics typical for mcCIC-Ka channels. Thus, in basolateral MTAL membranes, blockade of Cl- access to arginine or lysine residues on mmCIC-Ka by PGO results in Cl- channels having the functional characteristics of mcCIC-Ka channels.

Cl- channels in basolateral TAL membranes. XIX. Cytosolic Cl- regulates mmCIC-Ka and mcCIC-Ka channels

We evaluated the effects of culturing mouse MTAL cells under conditions that suppressed steady-state cytosolic Cl- on chloride channels fused into bilayers from basolateral vesicles of cultured MTAL cells. We used two agents to suppress Cl- entry: 10(-6) M PGE2 and 10(-4) M bumetanide. Basolateral Cl- channels from control cultured MTAL cells exhibited the signature characteristics of mmCIC-Ka channels: increased open-time probability (Po) either by raising cytosolic-face [Cl-] or, at 2 mM cytosolic Cl-, by adding (ATP + PKA), and first-order conductance kinetics. Either 10(-6) M PGE2 or 10(-4) M bumetanide in culture media reduced steady-state MTAL cytosolic Cl-. Chloride channels from these cells exhibited characteristics unique to CTAL mcCIC-Ka channels, namely: no augmentation of Po either by raising cytosolic Cl- or with cytosolic (ATP + PKA), and multi-ion occupancy. Semi-quantitative RT-PCR and real-time quantitative PCR showed that culturing MTAL cells with 10(-6) M PGE2 or 10(-4) M bumetanide reduced mRNA levels encoding mmCIC-Ka but not mRNA levels encoding mcCIC-Ka. However, when MTAL cells were cultured under control conditions, and then pre-incubated for 60 minutes with 10(-4) M bumetanide, cytosolic Cl- fell acutely but Cl- channels exhibited characteristics of mmCIC-Ka channels. Thus PGE2 and bumetanide, both of which lower steady-state MTAL cytosolic Cl- concentrations, inhibit either the transcriptional and/or the translational processes for mmCIC-Ka synthesis.

Cl channels in basolateral TAL membranes. XVII. Kinetic properties of mcClC-Ka, a basolateral CTAL Cl- channel

This paper describes the kinetics of Cl- flux through mcClC-Ka Cl- channels from basolateral membranes of mouse CTAL cells. We have cloned two separate but highly homologous Cl- channels, mmClC-Ka from cultured mouse MTAL cells and mcClC-Ka from cultured mouse CTAL cells. The mmClC-Ka and mcClC-Ka channels appear to mediate net Cl- absorption in the MTAL and CTAL, respectively. The kinetics of Cl- permeation through mmClC-Ka channels exhibit traditional criteria for a first-order process, including saturation kinetics. Thus mmClC-Ka channels operate functionally as if the channels were occupied by a single Cl- ion at any given time. In the present studies, we examined conductance-concentration relations in mcClC-Ka channels, and compared both mole-fraction effects and ion selectivity characteristics in mmClC-Ka and mcClC-Ka channels. In mcClC-Ka channels, we observed both self-block at high external Cl- concentrations and, at constant ionic strength, an anomalous mole-fraction effect using external solutions containing varying F-/Cl- concentrations. Neither effect was obtained in mmClC-Ka channels. These data are consistent with the possibility that Cl- permeation through mcClC-Ka channels involved multi-ion occupancy channels that expressed single-file behavior.

Cl- channels in basolateral TAL membranes. XVI. MTAL and CTAL cells each contain the mRNAs encoding mmClC-Ka and mcClC-Ka

BACKGROUND

Our prior data indicate that two separate but homologous basolateral chloride (Cl-) channels, mmClC-Ka and mcClC-Ka, are the principal mediators of net Cl- absorption in mouse medullary thick ascending limb (MTAL) and cortical thick ascending limb (CTAL) cells, respectively. In the present studies, we evaluated the possibility that there might be translational or post-translational suppression of mmClC-Ka and mcClC-Ka activity in CTAL and MTAL cells, respectively.

METHODS

Polymerase chain reaction (PCR) fragments were prepared that were highly specific for either mmClC-Ka or mcClC-Ka, the cDNAs encoding mmClC-Ka and mcClC-Ka, respectively.

RESULTS

Using reverse transcription (RT)-PCR with these highly specific products, mRNAs specific for non-homologous channel sequences in either mmClC-Ka or mcClC-Ka were present in both MTAL and CTAL cells.

CONCLUSIONS

Both mouse MTAL and CTAL cells contain the mRNAs encoding mmClC-Ka and mcClC-Ka. There may be translational or post-translational suppression of mmClC-Ka activity in CTAL cells, and of mcClC-Ka activity in MTAL cells.

Chloride channels in the loop of Henle

Cl- transport in the loop of Henle is responsible for reclamation of 25-40% of the filtered NaCl load and for the formation of dilute urine. Our understanding of the physiologic and molecular mechanisms responsible for Cl- reabsorption in both the thin ascending limb and thick ascending limb of Henle's loop has increased greatly over the last decade. Plasma membrane Cl- channels are known to play an integral role in transcellular Cl- transport in both the thin and thick ascending limbs. This review focuses on the functional characteristics and molecular identities of these Cl- channels, as well as the role of these channels in the pathophysiology of disease.

Relative efficacy of sildenafil compared to other treatment options for erectile dysfunction

OBJECTIVE

We examined and compared the efficacy of sildenafil in patients previously using other agents or devices for erectile dysfunction (ED) treatment.

METHODS

We identified 47 patients with organic ED who had tried other therapies (intracavernosal injection therapy [ICIT], intraurethral prostaglandin suppositories [IPS], vacuum erection devices [VEDs], or yohimbine) before using sildenafil. Comparisons of the efficacy of sildenafil to the previously used agent or device were assessed by telephone questionnaire. Responses were compared using nonparametric Wilcoxon rank sum and analysis of variance testing.

RESULTS

Sildenafil therapy was no more effective than ICIT or VEDs but was more effective than IPS. No significant difference occurred in response to sildenafil with age. Of 22 patients achieving erections adequate for intercourse with their previous therapy, 14 (63%) achieved equal or improved erections with sildenafil. Of the remaining 18 patients who had erections inadequate for intercourse with previous therapy, 5 (27%) had adequate erections with sildenafil.

CONCLUSIONS

Oral sildenafil therapy provides results comparable to those of other available ED treatment modalities. A trial of this drug in this patient population is warranted.

Cl(-) channels in basolateral TAL membranes XV. Molecular heterogeneity between cortical and medullary channels

We have isolated two new and highly homologous cDNAs, mmClC-Ka from mouse outer medulla and mcClC-Ka from mouse cortex. In both cases, mRNA was obtained from the indicated region and subjected to RT-PCR using primers from the nucleotide sequence of rbClC-Ka, which encodes basolateral Cl(-) channels (termed rbClC-Ka) in rabbit MTAL. The predicted protein products of mmClC-Ka and mcClC-Ka, mmClC-Ka and mcClC-Ka, respectively, were 85% homologous and had predicted molecular weights of 75 kDa. The predicted protein sequences for mmClC-Ka and rbClC-Ka had three cytosolic sites-threonine 185, threonine 187 and serine 270-which were absent in mcClC-Ka. These three moieties represent potential sites for phosphorylation of mmClC-Ka and rbClC-Ka, but not of mcClC-Ka, and may account for the failure of (ATP + PKA) to increase the open time probability P(o) in basolateral CTAL Cl(-) channels. We prepared antisense oligonucleotides specific for nonhomologous regions of these two cDNAs, mmAntisense for mmClC-Ka and mcAntisense for mcClC-Ka. Using anti-rbClC-Ka, a polyclonal antibody to rbClC-Ka, we found that, when transfected into cultured mouse MTAL and CTAL cells, mmAntisense suppressed the appearance of the 75 kDa band by 50% in vesicles from MTAL but not CTAL cells, while transfection of MTAL and CTAL cells with mcAntisense suppressed appearance of the 75 kDa band in vesicles from CTAL but not MTAL cells. mmAntisense transfection also prolonged the half-time (T(1/2), sec) for (36)Cl(-) efflux in cultured MTAL cells from 82.4 +/- 6.8 sec (sem) to 187.8 +/- 9.5 sec (n = 5; P = 0.0001) while mcAntisense transfection had no such effect. Conversely, in cultured CTAL cells, mcAntisense transfection prolonged the T(1/2) for (36)Cl(-) efflux from 80.9 +/- 6.3 sec to 191.8 +/- 6.5 sec (n = 5; P = 0.00005), while mmAntisense had no such effect. We conclude that mmClC-Ka and mcClC-Ka may encode the basolateral Cl(-) channels mediating net Cl(-) absorption in mouse MTAL and CTAL, respectively.

Cl- channels in basolateral TAL membranes. XIV. Kinetic properties of a basolateral MTAL Cl- channel

BACKGROUND

This article reports studies on the kinetics of chloride (Cl-) conductance in Cl- channels fused into bilayers from basolaterally enriched vesicles from rabbit outer medulla. A considerable body of evidence indicates that these channels represent rbClC-Ka, a 77 kDa kidney-specific protein of the ClC family of Cl- channels. rbClC-Ka, a candidate channel for mediating net Cl- absorption in the medullary thick ascending limb (MTAL), has been cloned from rabbit outer medulla and localized by immunofluorescence to basolateral membranes of the MTAL. Thus, this is the first account, to our knowledge, of the kinetics of ion permeation through a renal Cl- channel mediating net basolateral Cl- absorption in the thick ascending limb of Henle (TALH), and this channel may represent rbClC-Ka.

METHODS

The electrophysiological properties of these channels were studied by fusing basolaterally enriched MTAL vesicles into planar bilayer membranes.

RESULTS

Cl- conductance through these channels was concentration dependent and saturable. The relationship between gCl (pS) and symmetrical aqueous Cl- concentrations could be expressed in terms of the Michaelis equation with a limiting conductance (GClmax, pS) of 114 pS at infinitely high aqueous Cl- concentrations and a K1/2 of 163 mM Cl-. A log-log plot of the conductance-Cl- concentration relations, in the nonsaturating Cl- concentration range, had a slope of 0.91, that is, virtually unity. The relatively impermeant anion I- produced a voltage-dependent conductance blockade that could be overcome at high electric field strengths.

CONCLUSIONS

The experimental data described earlier here fulfill the traditional criteria for a first-order process with a single Cl- ion occupying these channels at a given time. Although the channels may contain multiple ion binding sites, the latter function, in integral kinetic terms, as a single rate-limiting locus.

Cl- channels in basolateral TAL membranes: XIII. Heterogeneity between basolateral MTAL and CTAL Cl- channels

BACKGROUND

Antidiuretic hormone (ADH) or adenosine 3', 5'-cyclic phosphate (cAMP) analogues augment net NaCl absorption in microperfused mouse medullary thick ascending limb (MTAL) segments but not in cortical thick ascending limb (CTAL) segments. This ADH-dependent MTAL effect is due to increased apical Na+/K+/2Cl- admittance and apical K+ recycling accompanied by a rise in calculated intracellular Cl- concentrations and by a threefold rise in basolateral Cl- conductance. rbClC-Ka, a 75.2 member of the ClC family of Cl- channels, mediates net Cl- absorption in the MTAL. The gating characteristics of rbClC-Ka channels from their intracellular surfaces are, to our knowledge, unique among Cl- channels. The channels are activated by small increases in intracellular Cl- (K1/2 = 10 mM Cl-). Adenosine triphosphate plus the catalytic subunit of protein kinase A (ATP + PKA) gate rbClC-Ka when cytosolic Cl- concentrations are 25 mM. Thus, in mouse MTAL segments, ADH-dependent rises in cytosolic Cl- are primarily responsible for basolateral Cl- conductance increases.

METHODS

These experiments compared the properties of Cl- channels fused into bilayers from basolaterally enriched vesicles from cultured mouse CTAL cells with rbClC-Ka channels.

RESULTS

The key findings were that anti-rbClC-Ka, antibody that recognizes and blocks rbClC-Ka, recognized and blocked basolateral Cl- channels in CTAL cells, that the extracellular faces of the CTAL channels were, like rbClC-Ka, substrate gated with a K1/2 of approximately 170 mM Cl-, and that, unlike rbClC-Ka channels, cytosolic faces of basolateral CTAL Cl- channels were not gated by either increasing cytosolic Cl- concentrations or cytosolic (ATP + PKA). This failure of activation of basolateral CTAL Cl- channels was confirmed using excised patch clamp studies. Finally, on Western blots, anti-rbClC-Ka recognized a 74 kDa band on basolateral CTAL vesicles.

CONCLUSIONS

Basolateral CTAL Cl- channels probably share a high degree of structural homology and possibly molecular mass with rbClC-Ka channels. However, significant differences between rbClC-Ka channels and CTAL Cl- channels account for the inability of increasing either cytosolic Cl- or (PKA + ATP) to raise Po in CTAL basolateral Cl- channels.

Cl- channels in basolateral renal medullary membranes. XII. Anti-rbClC-Ka antibody blocks MTAL Cl- channels

Cl- channels in the medullary thick ascending limb (MTAL) studied by either patch-clamp technique or reconstitution into lipid bilayers are activated by increases in intracellular Cl- concentrations. rbClC-Ka, a ClC Cl- channel, may represent this channel. We therefore evaluated the role of rbClC-Ka in transcellular MTAL Cl- transport in two separate ways. First, an antibody was raised against a fusion protein containing a 153-amino acid fragment of rbClC-Ka. Immunostaining of rabbit kidney sections with the antibody was localized to basolateral regions of MTAL and cortical thick ascending limb (CTAL) segments and also to the cytoplasm of intercalated cells in the cortical collecting duct. Second, Cl- uptake and efflux were measured in suspensions of mouse MTAL segments. Cl- uptake was bumetanide sensitive and was stimulated by treatment with a combination of vasopressin + forskolin + dibutyryl adenosine 3',5-cyclic monophosphate (DBcAMP). Cl- efflux was also increased significantly by vasopressin + forskolin + DBcAMP from 114 +/- 20 to 196 +/- 36 nmol.mg protein-1.45 s-1 (P = 0.003). Cl- efflux was inhibited by the Cl- channel blocker diphenylamine-2-carboxylate (154 +/- 26 vs. 70 +/- 21 nmol.mg protein-1.45 s-1, P = 0.003). An anti-rbClC-Ka antibody, which inhibits the activity of MTAL Cl- channels in lipid bilayers, reduced Cl- efflux from intact MTAL segments (154 +/- 28 vs. 53 +/- 14 nmol.mg protein-1.45 s-1, P = 0.02). These results support the view that rbClC-Ka is the basolateral membrane Cl- channel that mediates vasopressin-stimulated net Cl- transport in the MTAL segment.

Medullary thick limb basolateral Cl- channels

Chloride transport by the medullary thick ascending limb is a major determinant of urinary concentrating and diluting power and also of tubuloglomerular feedback. In this review, we discuss the electrophysiologic, regulatory, and molecular features of a Cl- channel present in basolateral membranes from the medullary thick ascending limb. Functional and immunohistochemical data support the view that rbCIC-Ka, a CIC Cl- channel cloned from rabbit kidney medulla, may be the Cl- channel which mediates basolateral Cl- efflux.

Cl- channels in basolateral renal medullary vesicles XI. rbClC-Ka cDNA encodes basolateral MTAL Cl- channels

The present experiments examined whether rbClC-Ka, a CIC family Cl-channel cDNA from rabbit outer medulla, encodes a basolateral membrane Cl- channel mediating net medullary thick ascending limb (MTAL) Cl- absorption. MTAL cells contain a Cl- channel having certain properties that make it a plausible candidate for the basolateral Cl- channel in that segment. Especially pertinent among properties is the fact that cytosolic Cl- increases in the range 2-25 mM activated these Cl- channels. Cultured mouse MTAL cells were grown in the presence of an antisense oligonucleotide specific for rbCIC-Ka or a random oligonucleotide with no complementarity to rbCIC-Ka. The abundance of Cl- channels was assessed by the frequency of incorporation of Cl- channels from membrane vesicles prepared from these cells into lipid bilayers and by Western blot analysis using an antiserum to the COOH terminus of the rbClC-ka protein. With the use of vesicles from untreated cells or cells treated with the random oligonucleotide, Cl- channels were incorporated into bilayers in 17% and 16% of trials, respectively. However, when vesicles were prepared from cells pretreated with antisense oligonucleotide, there was a virtual abolition of Cl- channel incorporation into bilayers but no effect on the frequency of K+ channel incorporation. In parallel with the reduction in Cl- channel incorporation, the abundance of rbClC-Ka protein was reduced approximately 50% on Western blots. Finally, exposure of Cl- channels in lipid bilayers to the rbClC-Ka antiserum resulted in a block in channel activity. These results support the contention that the basolateral Cl- channel mediating net Cl- absorption in the MTAL is encoded by rbClC-Ka.

Cl- channels in basolateral renal medullary vesicles. X. Cloning of a Cl- channel from rabbit outer medulla

These experiments were intended to identify candidate cDNAs which might encode basolateral membrane Cl- channels of the mTAL using a homology-based cloning strategy. We prepared a cDNA library using a 1.8 to 3.2 kb mRNA fraction from rabbit outer medulla that induces a Cl- conductance in cellular membranes of Xenopus laevis oocytes. The cDNA library was screened with two 32P-oligonucleotide probes corresponding to highly conserved sequences in other Cl- channels. We isolated two cDNAs: rbClC-Ka and rbClC-Kb. The protein sequences deduced from these two cDNAs had 99% homology. Using RT-PCR technology, cultured mouse mTAL cells were found to contain mRNA corresponding to those two cDNAs. Expression of the mRNAs corresponding to these two cDNAs was kidney-specific and was greater in rabbit renal medulla than rabbit renal cortex. Finally, by using RT-PCR technology in combination with microdissected glomeruli or tubule segments, we found mRNA for rbClC-Ka in glomeruli, proximal convoluted tubules, mTAL and cortical collecting tubules.

Cl- channels in basolateral renal medullary vesicles. IX. Channels from mouse MTAL cell patches and medullary vesicles

The experiments reported herein compared Cl- channels fused into bilayers from rabbit outer medullary vesicles with Cl- channels in excised patches of basolateral membranes from cultured mouse medullary thick ascending limb (MTAL) cells and evaluated whether the latter were plausible candidates for the Cl- channels mediating net NaCl absorption in microperfused mouse MTAL segments. The unique signature characteristics of Cl- channels incorporated into lipid bilayers from outer medullary vesicles include activation of open probability (Po) by increases in the Cl- concentrations bathing intracellular faces; activation of Po by protein kinase A (PKA) + ATP, when the Cl- concentrations bathing intracellular faces are low; and no effect of PKA + ATP on Po with high cytoplasmic-face Cl- concentrations. These same properties were observed in Cl- channels studied using excised patches of basolateral membranes from mouse MTAL cells. Moreover, in both bilayers and in excised patches, the sharpest fractional increase in Cl- channel Po occurred with cytosolic-face Cl- concentration increases to values similar to the antidiuretic hormone (ADH)-dependent values of intracellular Cl- activity in microperfused mouse MTAL segments, and these fractional Po increases were adequate to account quantitatively for the ADH-dependent increase in basolateral membrane Cl- conductance in microperfused mouse MTAL segments. Thus the excised-patch basolateral Cl- channels reported here are reasonable candidates for those mediating net Cl- absorption in the MTAL.

Cl- channels in basolateral renal medullary vesicles. VIII. Partial purification and functional reconstitution of basolateral mTAL Cl- channels

Cl- channels fused from basolateral mTAL membranes into planar bilayers have distinctive functional characteristics which, when taken together, are unique among Cl- channels. The properties of these 50 to 60 pS channels can account for the characteristics of basolateral Cl- conductances in microperfused mTAL segments and thus may mediate net basolateral Cl- absorption in the intact mTAL. In the present studies, we solubilized basolateral membranes from rabbit mTAL. Since basolateral mTAL Cl- channels contain arginine- and lysine-rich domains, we exposed these solubilized membranes to sequential cation- and anion-exchange chromatography. The bound and unbound eluates from cation- and anion-exchange chromatography were reconstituted into proteoliposomes which, when fused into bilayers, yielded Cl- channels whose properties were virtually identical to those described above for native basolateral mTAL channels fused into bilayers. As judged by valinomycin-sensitive conductive 36Cl- uptake, proteoliposomes reconstituted from the unbound eluates after anion-exchange chromatography were enriched at least 30-fold in Cl- channel activity and had about 30% of the total Cl- channel activity solubilized in native vesicles.

Cl- channels in basolateral renal medullary membranes: VII. Characterization of the intracellular anion binding sites

A unique property of basolateral membrane Cl- channels from the mTAL is that the Cl- concentration facing the intracellular aspects of these channels is a determinant of channel open time probability (Po). The K1/2 for maximal activation of Po by Cl- facing intracellular domains of these channels is 10 mM Cl-. The present experiments evaluated the nature of these Cl(-)-interactive sites. First, we found that the impermeant anion isethionate, when exposed to intracellular Cl- channel faces, could augment Po with a K1/2 in the range of 10 mM isethionate without affecting conductance (gCl, pS). Second, pretreatment of the solutions facing the intracellular aspects of the channels with either 1 mM phenylglyoxal (PGO), an arginine-specific reagent, or the lysine/terminal amine reagent trinitrobenzene sulfonic acid (TNBS, 1 mM), prevented the activation of Po usually seen when the Cl- concentration of solutions facing intracellular channel domains was raised from 2 to 50 mM. However, when the Cl- channel activity was increased by first raising the Cl- concentration bathing intracellular channel faces from 2 to 50 mM, subsequent addition of either PGO or TNBS to solutions bathing intracellular Cl- channel faces had no effect on Po. We conclude that the intracellular aspects of these Cl- channels contain Cl(-)-interactive loci (termed [Cl]i) which are accessible to impermeant anions in intracellular fluids and which contain arginine- and lysine-rich domains which can be inactivated, at low ambient Cl- or isethionate concentrations, by interactions with PGO or TNBS.

Pharmacokinetic characterization of the postdistribution phase of prohormone atrial natriuretic peptides amino acids 1-98, 31-67, and atrial natriuretic factor during and after rapid right ventricular pacing in dogs

Release rate constants and disappearance rate constants were determined for three atrial natriuretic peptides consisting of amino acids 1-98 (i.e., proANF 1-98), the midportion of the ANF prohormone consisting of amino acids 31-67 (i.e., proANF 31-67) and amino acids 99-126 (i.e., ANF) after right ventricular pacing at 100, 125, 150, and 180 bpm in six male mongrel dogs. Right atrial and femoral vein blood was obtained at baseline, and at 5, 12, 19, 26, 56, 86, 116, 146, and 206 minutes after right ventricular pacing. Resulting plasma concentration-time data derived parameters were compared. The disappearance rate constants for atrial and femoral venous proANF 1-98 were 0.0144 +/- 0.0087 (X +/- SD) and 0.0175 +/- 0.0075 min-1, respectively (t = 0.6158) and release rate constants were 0.1569 +/- 0.1504 and 0.0670 +/- 0.0393 min-1, respectively (t = 1.8269; P greater than .05). The proANF 31-67 disappearance rate constants were 0.0139 +/- 0.0082 and 0.0148 +/- 0.0132 min-1, respectively (t = 0.1192) and release rate constants were 0.0957 +/- 0.0414 and 0.1984 +/- 0.1762 min-1, respectively (t = 1.4812). The ANF elimination phase disappearance rate constants were 0.0663 +/- 0.0273 and 0.1116 +/- 0.0539 min-1 (t = 2.0923, P greater than .05), respectively, and the release rate constants were 0.1335 +/- 0.0532 and 0.1638 +/- 0.0520 min-1 (t = 0.7878, P greater than .05), respectively. These data indicate that proANF 1-98 and proANF 31-67 circulating beta post-distribution half-lives are approximately 45 minutes whereas beta half-life of ANF is 10 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Cl- channels in basolateral renal medullary vesicles: V. Comparison of basolateral mTALH Cl- channels with apical Cl- channels from jejunum and trachea

Cl- channels from basolaterally-enriched rabbit outer renal medullary membranes are activated either by increases in intracellular Cl- activity or by intracellular protein kinase A (PKA). Phosphorylation by PKA, however, is not obligatory for channel activity since channels can be activated by intracellular Cl- in the absence of PKA. The PKA requirement for activation of Cl- channels in certain secretory epithelia is, in contrast, obligatory. In the present studies, we examined the effects of PKA and intracellular Cl- concentrations on the properties of Cl- channels obtained either from basolaterally-enriched vesicles derived from highly purified suspensions of mouse medullary thick ascending limb (mTALH) segments, or from apical membrane vesicles obtained from two secretory epithelia, bovine trachea and rabbit small intestine. Our results indicate that the Cl- channels from mTALH suspensions were virtually identical to those previously described from rabbit outer renal medulla. In particular, an increase in intracellular (trans) Cl- concentration from 2 to 50 mM increased both channel activity (Po) and channel conductance (gCl, pS). Likewise, trans PKA increased mTALH Cl- channel activity by increasing the activity of individual channels when the trans solutions were 2 mM Cl. Under the latter circumstance, PKA did not activate quiescent channels, nor did it affect gCl. Moreover, when mTALH Cl- channels were inactivated by reducing cis Cl- concentrations to 50 mM, cis PKA addition did not affect Po. These results are consistent with the view that these Cl- channels originated from basolateral membranes of the mTALH. Cl- channels from apical vesicles from trachea and small intestine were completely insensitive to alterations in trans Cl- concentrations and demonstrated markedly different responses to PKA. In the absence of PKA, tracheal Cl- channels inactivated spontaneously after a mean time of 8 min; addition of PKA to trans solutions reactivated these channels. The intestinal Cl- channels did not inactivate with time. Trans PKA addition activated new channels with no effect on basal channel activity. Thus the regulation of Cl- channel activity by both intracellular Cl- and by PKA differ in basolateral mTALH Cl- channels compared to apical Cl- channels from either the tracheal or small intestine.

Exercise increases the circulating concentration of the N-terminus of the atrial natriuretic factor prohormone in normal individuals

Recently two peptides consisting of amino acids (aa) 1 to 30 and 31 to 67 of the N-terminus of the 126 aa prohormone of atrial natriuretic factor (proANF), as well as atrial natriuretic factor (ANF, aa 99 to 126; C-terminus), were found to have vasodilatory and natriuretic properties. These peptides, as well as ANF, circulate in humans as part of the N-terminus of the prohormone. To determine the effect of graded exercise on the circulating concentrations of the N-terminus and C-terminus of the ANF prohormone in normal persons, 12 healthy individuals (mean age 45 +/- 2 years) were evaluated before, for 2 hours after, and during bicycle exercise at a work loads of 25, 50, 75, 100, 125, 150, and 175 W. Both the N- and C-terminus of the ANF prohormone were released simultaneously with graded exercise in direct proportion to the intensity of the work load, measured objectively via maximal oxygen consumption (VO2max), respiratory quotient, and heart rate. Both the N-terminus and C-terminus of the ANF prohormone had strong positive correlations (p less than 0.001) with blood pressure, heart rate, VO2max, and respiratory quotient. Following exercise, the C-terminus returned to preexercise levels within 30 minutes, while the N-terminus remained significantly elevated at 30 and 60 minutes postexercise, reflecting the longer half-life of the N-terminus in the circulation.

Cl- channels in basolateral renal medullary membrane vesicles: IV. Analogous channel activation by Cl- or cAMP-dependent protein kinase

We examined the interactions of cAMP-dependent protein kinase and varying aqueous Cl- concentrations in modulating the activity of Cl- channels obtained by fusing basolaterally enriched renal outer medullary vesicles into planar lipid bilayers. Under the present experimental conditions, the cis and trans solutions face the extracellular and intracellular aspects of these Cl- channels, respectively. Raising the trans Cl- concentration from 2 to 50 mM increased the channel open-time probability, raised the unit channel conductance, and affected the voltage-independent determinant (delta G) of channel activity but not the gating charge (Winters, C.J., Reeves, W.B., Andreoli, T.E. 1990. J. Membrane Biol. 118:269-278). With 2 mM trans KCl, trans addition of the catalytic subunit of PKA (C-PKA) plus ATP increased channel open-time probability and altered the voltage-independent determinant of channel activity without affecting either unit channel conductance or gating charge. The effect was ATP specific, did not occur with (C-PKA plus ATP) addition to cis solutions, and was abolished by denaturing C-PKA. Finally, (C-PKA plus ATP) activation of channel activity was not detected with relatively high (50 mM) trans Cl- concentrations. These data indicate that (C-PKA plus ATP) might modulate Cl- channel activity by phosphorylation at or near the Cl(-)-sensitive site on the intracellular face of these channels.

Acute and sustained release of the atrial natriuretic factor prohormone N-terminus with acute myocardial infarction

This investigation was designed to determine if acute ischemic cardiac injury causes the release of the 98 amino acid (aa) N-terminus of the 126 aa atrial natriuretic factor prohormone (pro ANF). Seventeen patients with acute myocardial infarction, but without clinical evidence of congestive heart failure, had their circulating concentrations of the whole N-terminus (ie, pro ANF 1-98), the midportion of the N-terminus of the ANF prohormone (consisting of aa 31-67; pro ANF 31-67) and creatine phosphokinase (CPK) monitored daily for 14 days. All seventeen patients had elevated plasma pro ANF 1-98 and pro ANF 31-67 concentrations at the time of presentation. Maximal increase on day three post-infarction correlated with the size of infarction estimated by the maximal CPK (r = 0.675; p less than 0.05) but did not correlate with the amount of left ventricular dysfunction. Another three patients with acute myocardial infarction were treated with tissue plasminogen activator (tPA). The measured pro ANF 1-98 and pro ANF 31-67 levels in these patients were within our normal range and significantly lower (p less than 0.001) than seen in patients with acute myocardial infarction not given thrombolytic therapy. Six patients with unstable angina, likewise, had normal circulating pro ANFs 1-98 and 31-67 concentrations during prolonged episodes of chest pain. These data suggest that myocardial necrosis but not ischemia triggers the release of the entire 126 aa prohormone.

Change in plasma immunoreactive N-terminus, C-terminus, and 4,000-dalton midportion of atrial natriuretic factor prohormone with hemodialysis

Plasma concentrations of the immunoreactive N-terminus, C-terminus and 4,000-dalton midportion of the N-terminus of the atrial natriuretic factor (ANF) prohormone were measured before and after hemodialysis in 13 patients with end-stage renal disease. There was a significant (p less than 0.001) fall in the mean plasma concentration of the C-terminus (i.e. ANF, amino acids 99-126 of the prohormone) from 123 +/- 25 to 80 +/- 22 fmol/ml (mean +/- SEM) with dialysis. The whole N-terminus, on the other hand, increased from 9,336 +/- 2,011 to 11,021 +/- 2,134 fmol/ml after dialysis (p less than 0.002). Pro ANF 31-67 (i.e. amino acids 31-67 of the prohormone) increased postdialysis from 27,775 +/- 4,300 to 31,040 +/- 4,840 fmol/ml (p less than 0.003). Only 1.5% of pro ANF 1-98 and pro ANF 31-67 were cleared by the dialyzer membrane while 15% of ANF crossed the membrane. Thus, with hemodialysis the C-terminus decreases while the N-terminus and pro ANF 31-67 from the midportion of the N-terminus of the ANF prohormone increase in plasma which is partially explained by their respective abilities to cross the dialyzer membrane.

Increased release of the N-terminal and C-terminal portions of the atrial natriuretic factor prohormone during immersion-induced central hypervolemia in cirrhotic humans

The role of peptides from the N-terminus and C-terminus of the 126 amino acid (a.a.) atrial natriuretic factors (ANF) prohormone in modulating renal sodium and water handling in cirrhotic patients has not been defined. Eight cirrhotic individuals were evaluated; their mean basal circulating concentration of the C-terminus (a.a. 99-126; i.e., ANF) was 25 +/- 2 fmol/ml, not different from the 22 +/- 1 fmol/ml value found in 54 normal volunteers. On the other hand, the basal circulating concentrations of the whole N-terminus (a.a. 1-98) and the midportion of the N-terminus (namely a.a. 31-67; pro ANF 31-67) of the ANF prohormone in these cirrhotic subjects of 704 +/- 52 and 654 +/- 83 fmol/ml were significantly elevated (p less than 0.05; ANOVA) in comparison to control values (531 +/- 25, 317 +/- 22 fmol/ml, respectively). Following equilibration on a 10 mmol/day sodium diet, the responsiveness of the N-terminus and C-terminus of ANF prohormone to 3 h of water immersion, which induces marked acute central volume expansion, was evaluated in these 8 seated cirrhotic patients. There was a prompt increase in the circulating concentrations of immunoreactive (ir) pro ANF 1-98 (whole N-terminus), ir pro ANF 31-67, and ir ANF (C-terminus) within 15 min of immersion (p less than 0.05; ANOVA) compared to their preimmersion values. The response of circulating ir pro ANF 1-98, pro ANF 31-67, and ANF concentrations in these 8 cirrhotic subjects to immersion was significantly greater (p less than 0.05; ANOVA) than that of 7 healthy volunteers undergoing an identical 3-hour immersion study. With cessation of immersion, the C-terminus decreased within 30 min to a concentration not significantly different from preimmersion values, whereas the N-terminus and pro ANF 31-67 remained significantly elevated after 1 h.

Cl- channels in basolateral renal medullary membranes: III. Determinants of single-channel activity

We evaluated the effects of varying aqueous Cl- concentrations, and of the arginyl- and lysyl-specific reagent phenylglyoxal (PGO), on the properties of Cl- channels fused from basolaterally enriched renal medullary vesicles into planar lipid bilayers. The major channel properties studied were the anion selectivity sequence, anionic requirements for channel activity, and the effects of varying Cl- concentrations and/or PGO on the relation between holding voltage (VH, mV) and open-time probability (Po). Reducing cis Cl- concentrations, in the range 50-320 mM, produced a linear reduction in fractional open time (Po) with a half-maximal reduction in Po at cis Cl- approximately 170 mM. Channel activity was sustained by equimolar replacement of cis Cl- with F-, but not with impermeant isethionate. For trans solutions, the relation between Cl- concentration and Po was negatively cooperative, with 50% reduction in po at 10 mM Cl-. Reducing cis Cl- had no effect on the gating charge (Z) for channel opening, but altered significantly the voltage-independent energy (delta G) for channel opening. Phenylglyoxal (PGO) reduced Z and altered delta G for Cl- channel activity when added to cis, but not trans solutions. Furthermore, in the presence of cis PGO, reducing the cis Cl- concentration had no effect on Z but altered delta G. Thus we propose that cis PGO and cis Cl- concentrations affect separate sites determining channel activity at the extracellular faces of these Cl- channels.

Increased release of the N-terminus of the atrial natriuretic factor prohormone with increasing absolute atmospheres of pressure in a hyperbaric chamber and reversal with oxygen therapy

Increasing atmospheres of absolute pressure (ATA) on the cardiopulmonary system results in a marked diuresis. The present investigation was designed to determine if the diuresis observed with increasing ATA is associated with increased release of the N-terminus of the atrial natriuretic factor (ANF) prohormone that contains two potent diuresis-producing hormones consisting of amino acids (aa) 1-30 (pro ANF 1-30; long-acting sodium stimulator) and aa 31-67 (pro ANF 31-67; vessel dilator) of this 126 aa prohormone. Seven healthy volunteers (mean age, 31 years) had the circulating concentration of the N-terminus of the ANF prohormone evaluated at 1, 2, and 3 ATA in a monoplace hyperbaric chamber by two specific and sensitive radioimmunoassays that immunologically recognize (1) the whole 98 aa N-terminus and (2) the midportion of the N-terminus consistent with aa 31-67 (pro ANF 31-67). With increasing ATA from 1 (sea level) to 2 (equivalent to 33 feet of sea water), the circulating concentrations of both the whole N-terminus and pro ANF 31-67 increased threefold. At 3 ATA (66 feet of sea water), their circulating concentrations increased sixfold over their concentrations, at 1 ATA. With the addition of 100 percent O2 while at 3 and 2 ATA, the circulating concentrations of both the whole N-terminus and pro ANF 31-67 immediately decreased to their prehyperbaric ATA levels and remained there with further decompression to 1 ATA and removal of O2 supplementation. The increased circulating concentration of the N-terminus of the ANF prohormone containing two peptides with potent diuretic effects during increasing atmospheres of absolute pressure may help to explain the diuresis that has been observed with increasing ATA.

Increased circulating concentration of the N-terminus of the atrial natriuretic factor prohormone in persons with pheochromocytomas

To investigate the possible relationship of hypertension and the N-terminus of the atrial natriuretic factor (ANF) prohormone which contains two peptides [i.e. pro ANF-(1-30) and pro-ANF-(31-67)] with blood pressure-lowering effects, we examined the circulating levels of the N-terminus of the ANF prohormone in three patients with pheochromocytomas before surgery, during an increase in their blood pressure with surgical manipulation of their tumors, and after surgery when their blood pressures returned to normal. The circulating levels of the whole N-terminus [amino acids 1-98; pro-ANF-(1-98)] and pro-ANF-(31-67) from the midportion of the N-terminus of the ANF prohormone were increased 2-fold in patients with both extraadrenal and intraadrenal pheochromocytomas. In both the intraadrenal and extraadrenal patients N-terminus [pro-ANF-(1-98)] and pro-ANF-(31-67) circulating levels increased further during surgical manipulation and returned to normal after surgical removal of their respective tumors. Each of these pheochromocytomas was found to have pro-ANF-(1-30) and -(31-67)-binding sites that were functional, since they could enhance the guanylate cyclase-cGMP system 2-fold in these pheochromocytomas. The entire 126 amino acids of the prohormone were present within each of the pheochromocytomas, since both the whole N-terminus and C-terminus (i.e. ANF) of the prohormone were present. Examination of the pheochromocytomas by electron microscopy revealed electron-dense granules similar to those in the heart, which have been associated with the synthesis and storage of the ANF prohormone. We conclude that 1) the whole N-terminus [pro-ANF-(1-98)] and pro-ANF-(31-67) of the ANF prohormone circulate at higher concentrations in persons with pheochromocytomas and return to normal with removal of the tumors; 2) pheochromocytomas contain specific binding sites for pro-ANF-(1-30) and -(31-67); 3) these binding sites are functional, since pro-ANF-(1-30) and -(31-67) could enhance the enzyme guanylate cyclase within these tumors; and 4) the entire 126 amino acids of the ANF prohormone are present within these tumors, which have electron-dense granules associated with polypeptide hormone synthesis, suggesting that the ANF prohormone is being synthesized within the pheochromocytomas.

Plasma prohormone atrial natriuretic peptides 1-98 and 31-67 increase with supraventricular and ventricular arrhythmias

Recently two peptides consisting of amino acids (AA) 1-30 and 31-67 of the N-terminus of the 126 AA prohormone of atrial natriuretic factor (pro ANF) as well as atrial natriuretic factor (ANF, AA 99-126; C-terminus) were found to have vasodilatory and natriuretic properties. These peptides as well as ANF circulate in man as part of the N-terminus of the prohormone. To determine if the polyuria, associated with both ventricular and supraventricular arrhythmias, is associated with increased circulating concentrations of the N-terminus and C-terminus of the ANF prohormone, 20 individuals with spontaneous arrhythmias, including ten persons with atrial fibrillation, six with paroxysmal supraventricular tachycardia, and four with ventricular tachycardia, were evaluated before and after conversion to sinus rhythm. In all 20 patients, the circulating concentrations of the whole N-terminus (ie, AA 1-98), the midportion of the N-terminus (pro ANF 31-67) that circulates as a distinct 3900 molecular weight peptide after being proteolytically cleaved from the N-terminus, and the C-terminus were significantly higher (p less than 0.001) than their concentration in 54 persons with sinus rhythm. With conversion to sinus rhythm, the plasma C-terminus concentration of these 20 arrhythmia patients decreased to the level of persons with sinus rhythm within 30 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

The N-terminus of the atrial natriuretic factor prohormone in the pleural fluid of congestive heart failure patients

To investigate the possibility that the prohormone of atrial natriuretic factor might be secreted into the pleural fluid of patients with congestive heart failure who are known to have high concentrations of both the N-terminus and C-terminus of this prohormone circulating in their plasma, six patients with class 2 New York Heart Association classified congestive heart failure had the simultaneous measurement of plasma and pleural fluid N-terminal and C-terminal atrial natriuretic factor prohormone concentrations. The 98 amino acid (aa) N-terminus, the midportion of the N-terminus consisting of aa 31-67 of the 126 aa ANF prohormone (ie, pro ANF 31-67), and the C-terminus (aa. 99-126, ANF) were found in high concentrations in the pleural fluid of all of these patients. The concentrations of the N-terminus (ie, pro ANF 1-98), and pro ANF 31-67 in pleural fluid were nearly equal to their concentration in plasma of these patients. Their plasma levels were more than double the plasma concentrations of pro ANFs 1-98 and 31-67 in 54 persons without congestive heart failure. These preliminary findings demonstrate that all 126 amino acids of the ANF prohormone are present in pleural fluid of patients with congestive heart failure since both the 98 aa N-terminus and the C-terminus (aa 99-126) are present. Whether or not the N-terminus, which contains diuretic and natriuretic peptides, secretion into pleural fluid helps clear the fluid present in the lung in congestive heart failure could not be determined from the present investigation.

Isolation and characterization of cloned cDNAs encoding human liver chlordecone reductase

Chlordecone (Kepone), a toxic organochlorine pesticide, undergoes bioreduction to chlordecone alcohol in human liver. This reaction is controlled by a cytosolic enzyme, chlordecone reductase (CDR), which may be of the aldo-keto reductase family of xenobiotic metabolizing enzymes [Molowa et al. (1986) J. Biol. Chem. 261, 12624-12627]. To further investigate the primary structure and expression of CDR, we screened a library of human liver cDNAs cloned in the expression vector lambda gt11 and isolated an 800 bp cDNA that directed synthesis of a fusion protein recognized by polyclonal anti-CDR antibodies. Using this cDNA as a probe, we screened two human liver cDNA libraries and found several 1.2-kb cDNAs which would code for a polypeptide with 308 residues (35.8 kDa). However, a similar full-length cDNA, possibly the transcript of a pseudogene, contained an in-frame nonsense codon. The deduced protein sequence of CDR showed 65% similarity to the primary structure of human liver aldehyde reductase and 66% similarity to the inferred protein sequence of rat lens aldose reductase. A search of GenBank revealed significant nucleotide similarity to a cDNA coding for bovine lung prostaglandin f synthase and to a partial cDNA coding for frog lens rho-crystallin. Southern blot analysis of human genomic DNA displayed between 45 and 65 kilobases of DNA hybridizable to CDR cDNA and demonstrated several restriction fragment length polymorphisms among 26 individuals. Northern blot analysis of RNA from human, gerbil, rabbit, hamster, mouse, and rat livers disclosed hybridization with CDR cDNA only for the first three species.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased release of the N-terminal and C-terminal portions of the prohormone of atrial natriuretic factor during immersion-induced central hypervolemia in normal humans

The role of peptides from the N terminus and C terminus of the 126 amino acid atrial natriuretic factor (ANF) prohormone in modulating renal sodium and water handling has not been defined. Since water immersion to the neck (NI) provides an acute central volume expansion identical to that produced by 2 liters of saline but without plasma compositional change, immersion to the neck was used to assess the N-terminal and C-terminal portions of the ANF prohormone response to acute central blood volume expansion in seven seated sodium-replete normal subjects. Both the C terminus, which contains amino acids 99-126 and is identical to ANF, and the whole N terminus (i.e., amino acids 1-98) increased promptly with NI and peaked after 1 hr of immersion. A Mr 3900 peptide from the midportion of the N terminus consistent with amino acids 31-67 (i.e., pro-ANF-31-67) also increased with NI and followed a pattern of increasing circulating concentration nearly identical to that of the whole N terminus of the prohormone, except that its maximal concentration was at the second hour of the 3 hr of NI. With cessation of immersion, ANF decreased to preimmersion levels within 1 hr whereas the N terminus and pro-ANF-31-67, although their circulating concentrations were decreasing, were still significantly elevated at 1 hr. These findings suggest that the increase in plasma ANF, the N terminus of the ANF prohormone, and pro-ANF-31-67 from the midportion of the N terminus, with natriuretic properties similar to ANF, contribute to the natriuretic response to NI, implying a physiologic role for these atrial peptides in modulating volume homeostasis in humans.

Prohormone atrial natriuretic peptides 1-98 and 31-67 increase with exercise in congestive heart failure patients

Recently two peptides consisting of amino acids (a.a.) 1-30 and 31-67 of the N-terminus of the 126 a.a. prohormone of atrial natriuretic factor (pro ANF), as well as atrial natriuretic factor (ANF, a.a. 99-126; C-terminus) were found to have vasodilatory and natriuretic properties. These peptides, as well as ANF, circulate in man as part of the N-terminus of the prohormone. To determine the effect of graded exercise on the circulating concentration of the N-terminus and C-terminus of the ANF prohormone in persons with abnormal salt and water metabolism, 12 individuals with stable congestive heart failure (CHF) were evaluated before and after bicycle exercise testing and the results were subdivided based on the maximal exercise they could achieve. In all of the CHF patients, the circulating concentration of the whole N-terminus (ie, a.a. 1-98), the midportion of the N-terminus (pro ANF 31-67), which circulates as a distinct 3900 molecular weight (m.w.) peptide after being proteolytically cleaved from the N-terminus, and the C-terminus (ANF) increased with exercise. The patients who were able to achieve 100 and 125 watts of workload had a greater maximal oxygen consumption and, in general, a greater percent increase in the circulating concentration of both the N-terminus and the C-terminus of the ANF prohormone than those who had less exercise capacity. Evaluation of the echocardiographic, radionucleotide, and the exercise parameters revealed that the circulating concentrations of these atrial peptides correlated best with left atrial dimension, but that left ventricular systolic and diastolic dimensions also correlated positively with their concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute and sustained release of atrial natriuretic factor with acute myocardial infarction

The present investigation was designed to determine if acute ischemic cardiac injury causes the release of atrial natriuretic factor (ANF). Seventeen patients with acute myocardial infarction but without clinical evidence of congestive heart failure had their circulating concentration of ANF and creatine phosphokinase monitored daily for 14 days. All 17 patients had an elevated plasma ANF concentration at time of presentation. Maximal increase in ANF was on day 2 and 3 post-infarction. This maximal increase correlated with the size of infarction estimated by the maximal creatine phosphokinase concentration (r = 0.475; p less than 0.05), but did not correlate with the amount of left ventricular dysfunction. ANF began to decrease by day 4 post-infarction and was normal at 10 days post-infarction in 14 of the 17 (82%) patients. At 12 days post-infarction, all 17 patients had normal ANF levels. Another three patients with acute myocardial infarction were treated with tissue plasminogen activator (tPA). The measured ANF levels in these patients were within our normal range and were significantly lower (p less than 0.001) than those seen in patients with acute myocardial infarction not given thrombolytic therapy. Six patients with unstable angina likewise had normal circulating ANF concentrations during prolonged episodes of chest pain. These levels were also significantly lower (p less than 0.001) than the 17 patients with acute infarcts not given tPA. The distinct pattern of release of ANF may be useful as an adjunct to serum cardiac enzymes in determining if a myocardial infarction has occurred.

The N-terminus and a 4,000-MW peptide from the midportion of the N-terminus of the atrial natriuretic factor prohormone each circulate in humans and increase in congestive heart failure

Two peptides consisting of amino acids 1-30 and 31-67 of the N-terminus of the prohormone of atrial natriuretic factor (pro-ANF) that have vasodilatory and natriuretic properties were investigated to determine if they circulate in humans. Specific and sensitive radioimmunoassays were developed to amino acids 1-30, 31-67, and 99-126 of pro-ANF. Evaluation of human plasma that had been subjected to reverse-phase high-pressure liquid chromatography suggested that pro-ANFs 1-30 and 31-67 as well as ANF were distinct peaks in human plasma corresponding exactly to pure synthetic peaks of these peptides on high-pressure liquid chromatography. Molecular weight determination of the endogenous immunoreactive peptides measured in plasma by G-50 Sephadex gel permeation chromatography revealed that the pro-ANF 1-30 radioimmunoassay recognized a peptide of 10,000 MW, which is consistent with it measuring the whole N-terminus of pro-ANF (amino acids 1-98) but without ANF (C-terminus) attached to it. The pro-ANF 31-67 radioimmunoassay recognized mainly (more than 95%) a peptide of 3,900-4,000 MW, which corresponds closely with its actual molecular weight of 3,878. Our ANF radioimmunoassay recognizes a peptide in plasma of 3,000 MW with the known molecular weight of ANF being 3,081. The mean circulating concentrations of immunoreactive pro-ANF 1-98, pro-ANF 31-67, and ANF in 54 control subjects were 531 +/- 25, 371 +/- 18, and 22 +/- 1 fmol/ml (+/- SEM), respectively. Thirty patients with varying severity of congestive heart failure were also studied. The N-terminus, C-terminus, and pro-ANF 31-67 increased: twofold for New York Heart Association functional Class II, threefold to ninefold for Class III, and 10- to 20-fold for Class IV patients with congestive heart failure. Thus, the N-terminus and a 4,000-MW peptide from the midportion of the N-terminus of pro-ANF as well as ANF circulate normally and increased proportionately to the increasing severity of congestive heart failure. However, because the pro-ANF 31-67 radioimmunoassay was the only assay that discriminated between patients with Class I congestive heart failure and control subjects, this assay may be the most useful to accurately classify the severity of congestive heart failure.

Atrial natriuretic factor in the pleural fluid of congestive heart failure patients

To investigate the possibility that atrial natriuretic factor might be secreted into the pleural fluid of patients with congestive heart failure who are known to have high concentrations of this new peptide hormone circulating in their plasma, six patients with class 2 New York Heart Association classified congestive heart failure had simultaneos measurement of plasma and pleural fluid atrial natriuretic factor concentrations. Atrial natriuretic factor was found in high concentrations in the pleural fluid of all of these patients. The concentration of atrial natriuretic factor in pleural fluid was nearly equal to the concentration in plasma of these patients. Their plasma levels were double the plasma concentration of this peptide hormone in 54 persons without congestive heart failure. These preliminary findings demonstrate that atrial natriuretic factor is present in pleural fluid of patients with congestive heart failure, but whether or not this secretion of atrial natriuretic factor into the pleural fluid helps the lung clear the fluid present in the lung in congestive heart failure cannot be determined from the present investigation.

Prohormone atrial natriuretic peptides 1-30 and 31-67 increase in hyperthyroidism and decrease in hypothyroidism

Hyperthyroidism characteristically has natriuresis and vasodilation associated with it, whereas hypothyroidism is associated with impaired water excretion and vasoconstriction. This investigation was designed to determine if the plasma concentration(s) of three newly described hormones synthesized in the heart are increased in patients with hyperthyroidism and/or decreased in patients with hypothyroidism compared to normal subjects. The three hormones consist of amino acids 1-30, 31-67, and 99-126 (ANF) of the 126 amino acid prohormone of atrial natriuretic factor. Prohormone atrial natriuretic peptides (pro ANFs) 1-30, 31-67, and ANF were increased threefold, fourfold, and twofold respectively in hyperthyroid patients compared to the mean circulating concentration of 54 healthy persons without thyroid disease. Plasma concentrations of the three peptides in hypothyroid patients were only one-half that of the 54 persons without thyroid disease. With appropriate treatment of hyperthyroidism and hypothyroidism, the levels of the three peptides returned to normal. The peptide hormones increased proportionately with the increasing dosages of L-thyroxine of 50 micrograms/day and 100 micrograms/day in the hypothyroid patients. In persons with hypothyroidism complicated by congestive heart failure, the levels of pro ANFs 1-30, 31-67, and 99-126 were increased, demonstrating that abnormalities of salt and water metabolism are a strong stimulus to the release of these peptides.

Prohormone atrial natriuretic peptides 1-30, 31-67, and 99-126 increase in proportion to right ventricular pacing rate

To determine whether heart rate contributes to release of three new peptide hormones synthesized in the heart, right ventricular pacing at rates of 100, 125, 150, and 180 bpm was performed in six dogs with measurement of the plasma concentration of these peptides at each pacing rate while right atrial and systemic blood pressures were simultaneously monitored. These three peptides of the 126-amino-acid prohormone of atrial natriuretic factor (ANF), consisting of amino acids 1-30 (pro ANF 1-30), 31-67 (pro ANF 31-67), and 99-126 (ANF), increased incrementally at paced heart rates of 125, 150, and 180 bpm (r = 0.8, p less than 0.001). Right atrial pressure decreased with increasing heart rate but systemic blood pressure did not decrease until the heart rate was 180 bpm, at which time these peptides had obtained their maximal circulating concentrations. After pacing, mean right atrial pressure and levels of ANF returned to prepacing values within 30 minutes. Mean arterial blood pressure, on the other hand, increased throughout the 120-minute period after pacing. At 2 hours after pacing, levels of pro ANFs 1-30 and 31-67 were elevated compared with prepacing values. These data demonstrate that, at heart rates of 125 bpm and above, pro ANF 1-30, pro ANF 31-67, and ANF (99-126) are simultaneously and incrementally released in direct proportion to heart rate. The sustained elevation in pro ANFs 1-30 and 31-67 seen 2 hours after pacing suggests that they may contribute to the prolonged diuresis seen after cardiac pacing or tachycardia.

Increased circulating concentration of atrial natriuretic factor in persons with pheochromocytomas

To investigate the possible relationship of atrial natriuretic factor (ANF) to hypertension, we examined the circulating levels of ANF in 3 patients with pheochromocytomas before surgery, during increase of their blood pressure with surgical manipulation of their tumors, and after surgery when their blood pressures returned to normal. The circulating levels of ANF were increased 2-fold in patients with both extra-adrenal and intra-adrenal pheochromocytomas. In both the intra-adrenal and extra-adrenal patients their ANF levels increased further during surgical manipulation and returned to normal after surgical removal of their respective tumors. Each of these pheochromocytomas was examined and found to have atrial natriuretic receptors that were functional since ANF could enhance the guanylate cyclase - cyclic GMP system two-fold in these pheochromocytomas. We conclude that ANF circulates at higher concentrations in persons with pheochromocytomas and returns to normal with removal of the tumor. In addition, pheochromocytomas contain specific ANF receptors and ANF itself within these tumors.

Two new hormones: prohormone atrial natriuretic peptides 1-30 and 31-67 circulate in man

Two peptides consisting of amino acids 1-30 and 31-67 of the N-terminal end of the prohormone of atrial natriuretic factor (pro ANF) which vasodilate aortas in vitro, lower blood pressure in vivo, and have natriuretic properties were found to circulate in 54 normal human volunteers. The mean circulating concentration of pro ANF 1-30 was 1861 +/- 87 pg/ml (SEM) while pro ANF 31-67 mean concentration was 1478 +/- 71 pg/ml versus a level of 67 +/- 3 pg/ml for atrial natriuretic factor (ANF). In chronic renal failure their mean concentrations increased to 40,484 +/- 6,929 pg/ml (SEM), 108,566 +/- 16,888 pg/ml, and 348 +/- 81 pg/ml for pro ANFs 1-30 and 31-67 and ANF respectively. Since pro ANF 1-30 and pro ANF 31-67 circulate in man and have physiologic effects they meet the criteria of two new hormones.

Circadian rhythm of prohormone atrial natriuretic peptides 1-30, 31-67 and 99-126 in man

Two peptides consisting of amino acids 1-30 and 31-67 of the N-terminal end of the prohormone of the atrial natriuretic factor (pro ANF), vasodilate aortas in vitro, lower blood pressure in vivo, and have natriuretic properties similar to the atrial natriuretic factor (ANF, amino acids 99-126 of the prohormone). It has been recently discovered that pro ANF 1-30 and pro ANF 31-67 as well as ANF circulate in man. To determine if these three peptide hormones have a circadian variation in their circulating plasma concentrations, eight housestaff volunteers were studied on a day when they were in the hospital for 24 hr. These 5 men and 3 women, ages 25 to 39 had blood samples taken at 0800, 1200, 1600, 2000, 0000, 0400 and 0800 on the following day. One-half of these house officers were up all night while the other half went to sleep from midnight to 0800 and had their 0400 plasma samples drawn while in a supine position. The peak level for all three peptide hormones was at 0400 for both supine and upright subjects. It was concluded that there are circadian rhythms in normal, active people of these three peptide hormones, whose peak levels are at 0400 irrespective of posture.