bluuebunny/crossref_metadata_2025 huggingface dataset:
Hormonal regulation of the Na(+)-K(+)-ATPase: mechanisms underlying rapid and sustained changes in pump activity
Authors: Ewart H. S. , Klip A.
Published: December 2017

The sodium-potassium-activated adenosinetriphosphatase (Na(+)-K(+)-ATPase; Na(+)-K+ pump) is a ubiquitous plasma membrane enzyme that catalyzes the movement of K+ into cells in exchange for Na+. In addition, it provides the driving force for the transport of other solutes, notably amino acids, sugar, and phosphate. The regulation of Na(+)-K(+)-ATPase in various tissues is under the control of a number of circulating hormones that impart both short- and long-term control over its activity. The molecular mechanisms by which hormones alter Na(+)-K(+)-ATPase activity have only begun to be studied. In this review, we assess the acute and long-term actions of a number of hormones (aldosterone, thyroid hormone, catecholamines, insulin, carbachol) on the Na(+)-K+ pump. The long-term regulation exerted by thyroid hormone and aldosterone is mediated by changes in gene expression. The short-term regulation exerted by catecholamines is mediated by reversible phosphorylation of the pump catalytic subunit. Recent evidence supports regulation of the pump by phosphorylation in vitro and in intact cells. Finally, in some tissues the rapid action of insulin, aldosterone, and carbachol involves changes in the subcellular distribution of pump units.
Ca2+ release and activation of K+ and Cl- currents by extracellular ATP in distal nephron epithelial cells
Authors: Nilius B. , Sehrer J. , Heinke S. , Droogmans G.
Published: December 2017

We have measured ionic currents and changes in intracellular Ca2+ concentration ([Ca2+]i) induced by extracellular ATP in single epithelial cells of the distal nephron from toad (A6 cells). ATP increased [Ca2+]i and concomitantly activated ionic currents. The ATP concentration for half-maximal increase in [Ca2+]i was approximately 10 microM. Current activation and elevation of [Ca2+]i also occurred in Ca(2+)-free bath solutions but were abolished by loading the cells via the patch pipette with 10 mM 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA) or by preincubating the cells with 10 microM BAPTA-acetoxymethyl ester for 120 min. ATP-activated currents reversed at -53.9 +/- 1.9 mV (n = 22). Tetraethylammonium (TEA, 25 mM), a K+ channel blocker, partially blocked this current but did not affect the Ca2+ transients. The TEA-insensitive component of the current reversed close to Cl- equilibrium potential. 5-Nitro-2-(3-phenylpropylamino) benzoic acid, a putative Cl- channel blocker (100 microM), abolished nearly completely the ATP-activated current. Suramin (100 microM), a P2-purinergic receptor antagonist, strongly attenuated both Ca2+ transients and currents. In cell-attached patches, single channel currents activated by ATP could be observed, i.e., an inwardly rectifying K+ channel with a slope conductance for inward currents of approximately 32 pS and an ohmic Cl- channel with a conductance of 34 pS. It is concluded that ATP activates both Cl- and K+ channels in distal nephron epithelial cells by a Ca(2+)-dependent mechanism.
Pattern of rat intestinal brush-border enzyme gene expression changes with epithelial growth state
Authors: Hodin R. A. , Chamberlain S. M. , Meng S.
Published: December 2017

Enterocyte growth and differentiation occur simultaneously within the epithelium, but little is known regarding any relationship between these two processes. Four rat models of small intestinal epithelial hypo- and hyperplasia (neonatal ontogeny, fasting/refeeding, hypo-/hyperthyroidism, and bombesin treatment) were used to study the regulation of enterocyte gene expression in relation to epithelial growth state. Mucosal scrapings, as well as crypt and villus cell populations, were subjected to Northern blot analyses using radiolabeled cDNA probes corresponding to lactase, intestinal alkaline phosphatase, villin, ornithine decarboxylase (ODC), and the actin control. In all four models, the hypoplastic (atrophic) condition is characterized by high levels of lactase and low levels of the 3.0-kb intestinal alkaline phosphatase mRNA, whereas under hyperplastic conditions this pattern is reversed. The changes in intestinal alkaline phosphatase and lactase are qualitatively similar along the longitudinal axis of the intestine and are proportional to the degree of hyperplasia, as verified by ODC mRNA levels. Furthermore, the crypt-villus axis of differentiation is maintained regardless of epithelial growth state. In conclusion, the pattern of brush-border enzyme gene expression changes as a function of epithelial growth state, indicating a previously unrecognized degree of plasticity to the state of enterocyte differentiation.
Mutational analysis of transmembrane histidines in the amiloride-sensitive Na+/H+ exchanger
Authors: Wang D. , Balkovetz D. F. , Warnock D. G.
Published: December 2017

The histidine-reactive reagent, diethyl pyrocarbonate (DEPC) inhibits the human amiloride-sensitive Na+/H+ exchanger (NHE1) in stably transfected fibroblasts. NHE1 was protected by cimetidine and amiloride from DEPC, and DEPC inhibition was reversed with hydroxylamine, suggesting a role for critical histidine groups in NHE activity. We replaced the histidines (H) in putative transmembrane domains (H35, H120, H349) with glycine (G) using site-directed mutagenesis. There was no significant change in NHE activity of the H120G; H349G; H120,349G; and H35,120,349G mutants compared with wild type. The 50% inhibition concentration values for amiloride, ethyl isopropyl amiloride (EIPA), and cimetidine of the H349G mutant were significantly increased compared with the wild-type NHE1. We also examined the DEPC effect on the transport activity of the triple histidine mutant (H35,120,349G) and found that NHE1 activity was still inhibited by DEPC with reversal by hydroxylamine and protected by amiloride and cimetidine. Kinetic analysis of DEPC inhibition indicated that two "critical" histidine residues are required for NHE transport activity. Substitutions of H349 with asparagine (N), glutamine (Q), serine (S), tyrosine (Y), valine (V), leucine (L), and phenylalanine (F) were also examined. There were no changes in NHE activity of these mutants compared with wild type. The H349G and H349L mutants became more resistant to amiloride, whereas the H349Y and H349F mutants became more sensitive to amiloride. The H349S (mimics NHE3) and H349Y (mimics NHE4) mutations had only modest effects on amiloride sensitivity. These results indicate that H349 affects the interaction of NHE1 with its inhibitors, even though substitutions at this site, per se, do not appear to explain the differences in amiloride sensitivity between different NHE isoforms. Despite clear-cut effects of the H349G mutation on the competitive interaction of NHE1 with cimetidine and EIPA, this mutation did not affect the affinity of NHE1 for its cationic substrates (Na+, Li+).
Functional and energetic effects of the inotropic agents EMD-57033 and BAPTA on the isolated rat heart
Authors: Grandis D. J. , DelNido P. J. , Koretsky A. P.
Published: December 2017

This investigation studied the functional and energetic effects of the novel positive inotropic agent EMD-57033 and the negative inotropic agent 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) in the paced Langendorff-perfused rat heart. EMD-57033 is a calcium-sensitizing agent that has previously been shown to increase contractility without affecting calcium transients. Its effects were compared with that of dobutamine, which increases contractility by increasing calcium transient amplitude. EMD-57033 (2 microM) and dobutamine (0.2 microM) induced a 40% increase in developed pressure. Myocardial oxygen consumption (MVO2) increased significantly with dobutamine. However, there was no significant change in MVO2 with EMD-57033. There was no change in phosphate metabolite concentrations as detected by 31P-nuclear magnetic resonance with either agent. Lactate production and basal metabolism were unaffected by either agent. Thus EMD-57033 increased contractility in a more energetically economical manner than did dobutamine. Contractility was decreased with BAPTA, an intracellular calcium chelator that decreases contractility by binding free calcium. The metabolic effects of BAPTA (2.2 microM) were compared with those of verapamil (10 nM), an agent which decreases calcium fluxes. Both agents decreased developed pressure 60%. MVO2 decreased 14% with BAPTA and 50% with verapamil. Neither agent altered the concentrations of phosphate metabolites, lactate production, or basal metabolism. Thus BAPTA lowered contractility in a less energetically economical manner than verapamil. These data suggest that in rat hearts, inotropic agents with different effects on calcium handling have different effects on energetics.
Cardiac ATP-sensitive K+ channels: regulation by intracellular nucleotides and K+ channel-opening drugs
Authors: Terzic A. , Jahangir A. , Kurachi Y.
Published: December 2017

ATP-sensitive K+ (KATP) channels are present at high density in membranes of cardiac cells where they regulate cardiac function during cellular metabolic impairment. KATP channels have been implicated in the shortening of the action potential duration and the cellular loss of K+ that occurs during metabolic inhibition. KATP channels have been associated with the cardioprotective mechanism of ischemia-related preconditioning. Intracellular ATP (ATPi) is the main regulator of KATP channels. ATPi has two functions: 1) to close the channel (ligand function) and 2) in the presence of Mg2+, to maintain the activity of KATP channels (presumably through an enzymatic reaction). KATP channel activity is modulated by intracellular nucleoside diphosphates that antagonize the ATPi-induced inhibition of channel opening or induce KATP channels to open. How nucleotides will affect KATP channels depends on the state of the channel. K+ channel-opening drugs are pharmacological agents that enhance KATP channel activity through different mechanisms and have great potential in the management of cardiovascular conditions. KATP channel activity is also modulated by neurohormones. Adenosine, through the activation of a GTP-binding protein, antagonizes the ATPi-induced channel closure. Understanding the molecular mechanisms that underlie KATP channel regulation should prove essential to further define the function of KATP channels and to elucidate the pharmacological regulation of this channel protein. Since the molecular structure of the KATP channel has now become available, it is anticipated that major progress in the KATP channel field will be achieved.
Role of [Na+]i and [Ca2+]i in nicotine-induced norepinephrine release from bovine adrenal chromaffin cells
Authors: Gerber S. H. , Haunstetter A. , Kruger C. , Kaufmann A. , Nobiling R. , Haass M.
Published: December 2017

Intracellular free sodium ([Na+]i) and calcium ([Ca2+]i) concentrations were determined by sodium-binding benzofuran isophthalate (SBFI) and fura 2 microfluorimetry, respectively, in bovine adrenal chromaffin cells (BCC). Validation of SBFI microfluorimetry by in vitro and in vivo calibration revealed a reliable assessment of [Na+]i within a range of 1-30 mM in single BCC. Nicotine (0.1-10 microM) induced concentration-dependent increases of both [Na+]i (from 3.3 +/- 0.1 to 25.6 +/- 0.4 mM, n = 76, P < 0.001) and [Ca2+]i (from 64 +/- 1 to 467 +/- 16 nM, n = 87, P < 0.001), which were accompanied by an increase in [3H]norepinephrine (NE) release. Consistent with an exocytotic release mechanism, nicotine-induced increments of [Ca2+]i and [3H]NE release were reduced under calcium-free conditions and by gadolinium chloride (40 microM), whereas [Na+]i was not affected. In contrast, a parallel attenuation of nicotine-evoked changes in [Na+]i, [Ca2+]i, and [3H]NE release was observed during reduction of the extracellular sodium concentration. The nicotine-evoked responses were neutralized by the nicotinic receptor antagonist hexamethonium (100 microM) but not by blockade of voltage-dependent sodium channels (1 microM tetrodotoxin). In conclusion, the nicotine-induced exocytotic release of [3H]NE is triggered by an increase in [Ca2+]i, which is facilitated by sodium influx through the nicotinic receptor ionophore.
[Ca2+]i transients in hypertensive and postinfarction myocytes
Authors: Zhang X. Q. , Moore R. L. , Tenhave T. , Cheung J. Y.
Published: December 2017

Changes in intracellular calcium concentration ([Ca2+]i) in paced fura 2-loaded myocytes isolated from Sham, renovascular hypertensive (Hyp), and myocardial-infarcted (MI) rats were examined. Compared with controls, Hyp myocytes paced at physiological rates had similar systolic but elevated diastolic [Ca2+]i. By contrast, systolic [Ca2+]i was significantly lower and diastolic [Ca2+]i higher in MI myocytes. The different patterns of alterations in [Ca2+]i dynamics in Hyp and MI myocytes may partly explain predominantly diastolic dysfunction in hypertensive hearts and systolic dysfunction in hearts surviving MI. In the presence of 1 microM isoproterenol, both Hyp and MI myocytes had much lower systolic [Ca2+]i when compared with their respective controls. Isoproterenol restored the elevated diastolic [Ca2+]i in Hyp myocytes toward normal but had no effect on the intrinsic differences in diastolic [Ca2+]i between Sham and MI myocytes. The observation that isoproterenol lowers diastolic [Ca2+]i in Hyp myocytes toward normal may provide a cellular mechanism for the lack of efficacy of beta-adrenergic blockers to improve diastolic compliance in patients with hypertensive hypertrophic cardiomyopathy.
Induction of NG-monomethyl-L-arginine uptake: a mechanism for differential inhibition of NO synthases?
Authors: Bogle R. G. , MacAllister R. J. , Whitley G. S. , Vallance P.
Published: December 2017

The properties, selectivity, and regulation of NG-monomethyl-L-arginine (L-NMMA) uptake were examined in a human cultured vascular endothelial cell line SGHEC-7 and murine macrophage J774 cells. In both cell types the uptake of L-[14C]NMMA was time and temperature dependent. In endothelial cells L-[14C]NMMA uptake occurred via a single saturable carrier-mediated system with an apparent Kt of 77 +/- 2 microM. In murine macrophage cells a saturable component with an apparent Kt of 51 +/- 6 microM and a nonsaturable component of L-NMMA uptake were identified. In both cell types uptake of L-[14C]NMMA (10 microM) was significantly inhibited in the presence of 100-fold excess of L-NMMA, asymmetric NG,NG-dimethyl-L-arginine (ADMA), symmetric NG,NG-dimethyl-L-arginine (SDMA), L-canavanine, L-arginine, and to a lesser extent D-arginine. Uptake of L-[14C]NMMA was inhibited weakly (approximately 30%) by NG-nitro-L-arginine, NG-nitro-L-arginine methyl ester, aminoguanidine, and L-citrulline. Incubation of macrophage J774 cells with lipopolysaccharide (LPS; 1 or 10 micrograms/ml) resulted in the induction of nitric oxide (NO) synthase activity determined by the accumulation of nitrite in the culture medium. In these cells an enhanced uptake of L-NMMA uptake was observed which was prevented by pretreatment with cycloheximide (1 microM) but not dexamethasone (1 microM).(ABSTRACT TRUNCATED AT 250 WORDS)
Water channel-carrying vesicles in the rat IMCD contain cellubrevin
Authors: Franki N. , Macaluso F. , Schubert W. , Gunther L. , Hays R. M.
Published: December 2017

Antidiuretic hormone (arginine vasopressin) induces a cyclic process of docking, fusion, and endocytosis of water channel-containing vesicles in the collecting duct. There is now evidence that docking and endocytosis are mediated by an array of proteins associated with vesicles and target membranes. In recent studies, we have shown that cellubrevin, a member of the vesicle-associated membrane protein family, as well as other docking proteins, are expressed in the rat inner medullary collecting duct. We now show by immunogold electron microscopy that cellubrevin is present on vesicles containing water channels, that it is associated with both coated and uncoated vesicles, and that it is present on the apical membrane. Cellubrevin, therefore, is in a position to mediate one or more steps in arginine vasopressin-induced water channel cycling.
Control of beta-myosin heavy chain expression in systemic hypertension and caloric restriction in the rat heart
Authors: Swoap S. J. , Haddad F. , Bodell P. , Baldwin K. M.
Published: December 2017

In the rat left ventricle, both pressure overload induced by abdominal aortic constriction (Abcon) and caloric restriction (CR) induce an increase in the steady-state level of the beta-myosin heavy chain (MHC) protein and mRNA. Both models also induce a concomitant decrease in the alpha-MHC protein and mRNA. The goals of this study were to 1) determine if the changes in MHC expression in the models are due to altered transcription and 2) identify the relative levels of some key factors interacting with the regulatory regions of these genes. Female Sprague-Dawley rats were randomly assigned to the following groups: 1) normal control (NC), 2) Abcon, and 3) CR. After 5 wk of experimental manipulations, myocardial nuclei were isolated. These nuclei were used for 1) nuclear run-on assays or 2) nuclear extract, which was prepared and used for gel mobility shift assays (GMSAs). Nuclear run-on assays demonstrated that the increase in beta-MHC mRNA and protein expression in both Abcon and CR can be at least partially attributed to increased transcription. The concomitant decrease in alpha-MHC content can similarly be attributed to a decrease in transcription of this gene. Furthermore, GMSAs demonstrate that nuclear extract from each group interact differently with certain elements known to be important for expression in vitro. CR nuclear extracts have a 25.6 +/- 7.2% decrease (P < 0.05 vs. NC) in interaction with a thyroid-responsive element, a potential repressor of beta-MHC transcription.(ABSTRACT TRUNCATED AT 250 WORDS)
Immunolocalization of rat cardiac beta-MHC protein expression in systemic hypertension and caloric restriction
Authors: Swoap S. J. , Gastellum C. , Bodell P. , Baldwin K. M.
Published: December 2017

Previous studies have shown that both systemic hypertension induced by abdominal aortic constriction (Abcon) and 50% caloric restriction (CR) increase left ventricular (LV) beta-myosin heavy chain (MHC) protein expression in the rat. However, these two physiological states have different effects on hemodynamic load, and information regarding beta-MHC localization across the LV wall in these two models may provide insight into the process of adaptation to chronic stress among myocardial cells. Thus the goal of this study was to determine the pattern of beta-MHC protein expression across the LV wall in Abcon and CR models using a beta-MHC-specific antibody. Adult female Sprague-Dawley rats (approximately 225-250 g) were randomly assigned to one of three groups: 1) normal control (NC), 2) Abcon, and 3) CR. After a treatment period of 5 wk, Abcon LVs hypertrophied 52% relative to NC, accompanying the 42% increase in mean blood pressure. CR rats, however, had a normal LV weight-to-body weight ratio. The relative content of LV beta-MHC protein expression, as assessed by native gel electrophoresis, increased from 3% in NC to 25 and 41% in Abcon and CR rats, respectively. Immunohistochemical analysis of beta-MHC expression demonstrated that the increase in beta-MHC protein in the Abcon group occurred primarily on the endocardial side of the LV. In contrast, the increase in beta-MHC protein in the CR LV occurred equally across the entire LV wall. This suggests that CR has a global effect on MHC isoform expression in LV myocardial cells.(ABSTRACT TRUNCATED AT 250 WORDS)x
Altered hepatic localization and expression of occludin after common bile duct ligation
Authors: Fallon M. B. , Brecher A. R. , Balda M. S. , Matter K. , Anderson J. M.
Published: December 2017

Epithelial tight junctions form a regulated barrier that seals the paracellular space and prevents mixing of luminal contents with the interstitium. This barrier is composed of a group of proteins including the putative “sealing” protein occludin that appears to bind directly to a cytoplasmic junction protein, ZO-1. To study the interaction and regulation of these two components when paracellular integrity is altered, we assessed protein expression and immunofluorescent (IF) localization of ZO-1 and occludin in a rat model of hepatocyte tight junction damage induced by common bile duct ligation (CBDL). Protein levels were detected in liver by immunoblotting and IF localization by 3-dimensional reconstruction of serial 0.5-micron confocal microscopic optical sections. As previously described, ZO-1 protein levels progressively increased to threefold control levels 9 days after CBDL. In contrast, occludin protein levels decreased by 50% within 2 days after CBDL and returned to control values by 9 days. In control IF sections, ZO-1 and occludin colocalized, forming thin continuous staining outlining canaliculi. After CBDL, ZO-1 staining appeared discontinuous, and a punctate pericanalicular accumulation of signal developed around junctional areas. Occludin staining was also discontinuous after CBDL, but, in contrast to ZO-1, was not punctate and remained localized either in a linear fashion along canalicular margins or in a homogeneous fashion in immediately surrounding areas. CBDL results in changes in the expression and localization of the putative tight junction sealing protein occludin in hepatocytes that are distinct from those observed for the peripheral membrane tight junction protein ZO-1.(ABSTRACT TRUNCATED AT 250 WORDS)
Chronic enhancement of neuromuscular activity increases acetylcholinesterase gene expression in skeletal muscle
Authors: Sveistrup H. , Chan R. Y. , Jasmin B. J.
Published: December 2017

We determined levels of mRNA encoding acetylcholinesterase (AChE) in muscles of rats subjected to chronic enhancement of neuromuscular activation. After 8 wk of voluntary wheel running, extensor digitorum longus (EDL) muscles displayed a 72% increase in total AChE activity as a result of a selective threefold increase in the G4 content. Soleus muscles, on the other hand, exhibited a 30% decrease in A12 while displaying a small (33%) increase in total AChE activity. These enzymatic adaptations were paralleled by increases in the levels of AChE mRNAs in both EDL (32%; P < 0.03) and soleus (42%; P < 0.02) muscles. In addition, compensatory hypertrophy of the plantaris muscle increased total AChE activity by 75%. This change was reflected by an elevation in all AChE molecular forms with A12 (89%) and A8 (179%) showing the most prominent increases. Similar to exercise-trained muscles, hypertrophied plantaris muscles displayed an increase in AChE transcripts (25%; P < 0.04). These results indicate that increases in neuromuscular activity modulate expression of the AChE gene in vivo and suggest the involvement of pretranslational regulatory mechanisms in the adaptive response of AChE to enhanced neuromuscular activation.
Copper transport and kinetics in cultured C6 rat glioma cells
Authors: Qian Y. , Tiffany-Castiglioni E. , Harris E. D.
Published: December 2017

C6 rat glioma cells accumulate and efflux 67Cu. Both processes showed saturation kinetics with increasing 67Cu concentration. The Michaelis constant (Km) for uptake was 0.63 +/- 0.14 microM; maximum velocity (Vmax) was 3.29 +/- 0.57 pmol Cu.mg protein-1.min-1. The Km for efflux was 0.15 +/- 0.06 microM; Vmax was 1.08 +/- 0.71 pmol Cu.mg protein-1.min-1. p-Chloromercuribenzoate (p-CMB) totally blocked 67Cu efflux but had no effect on Km or Vmax of uptake. Total 67Cu in the cell after 50 min was partitioned equally between particulate and soluble fractions. p-CMB-treated cells accumulated more 67Cu, but < 10% was bound to the particulate (membrane) fraction. Pb also increased 67Cu accumulation without affecting Km and Vmax of 67Cu uptake. These data suggest that carriers for import and export of Cu in C6 cells are distinct or operate in two different cellular environments. Efflux is a sulfhydryl-dependent process subject to inhibition by Pb. The data are consistent with a P-type ATPase in the efflux of Cu from cells and the potential for Pb to inhibit the efflux mechanism.
Pharmacology of ATP-sensitive K+ currents in smooth muscle cells from rabbit mesenteric artery
Authors: Quayle J. M. , Bonev A. D. , Brayden J. E. , Nelson M. T.
Published: December 2017

The inference that ATP-sensitive K+ (KATP) channels are involved in arterial responses to the synthetic K+ channel openers, hypoxia, adenosine, and calcitonin gene-related peptide, has relied on the sensitivity of these responses to the sulfonylureas glibenclamide and tolbutamide and to tetraethylammonium (TEA+). The inhibition of KATP currents by glibenclamide, tolbutamide, and TEA+ was investigated in single smooth muscle cells from rabbit mesenteric artery by use of the whole cell patch-clamp technique. The synthetic K+ channel openers pinacidil (half-activation 0.6 microM), cromakalim (half-activation 1.9 microM), and diazoxide (half-activation 37.1 microM) activated K(+)-selective currents that were blocked by glibenclamide. Elevation of pipette (intracellular) ATP concentration decreased K+ currents induced by pinacidil. Half-inhibition of KATP currents by glibenclamide and tolbutamide occurred at 101 nM and 351 microM, respectively. KATP currents were also inhibited by external TEA+, with half-inhibition at 6.2 mM. The results indicate that glibenclamide is an effective inhibitor of KATP channels in arterial smooth muscle and that tolbutamide and TEA+ are much less effective. Furthermore, these results support numerous functional studies that have demonstrated that the vasorelaxations to K+ channel openers are inhibited by < 10 microM glibenclamide but not by < 1 mM TEA+.
Warming macrophages to febrile range destabilizes tumor necrosis factor-alpha mRNA without inducing heat shock
Authors: Ensor J. E. , Crawford E. K. , Hasday J. D.
Published: December 2017

We have previously reported that sustained tumor necrosis factor (TNF)-alpha expression is suppressed by temperatures in the febrile range in human macrophages. In this study, we examined the mechanisms of high-temperature-induced macrophage TNF suppression in the RAW 264.7 macrophage cell line. Incubating lipopolysaccharide (LPS)-stimulated RAW 264.7 cells at 40 degrees C reduced TNF secretion by 92% and peak TNF mRNA levels by 43% compared with cells incubated at 37 degrees C (P < 0.05) but did not affect levels of glyceraldehyde-3-phosphate dehydrogenase, beta-actin, or interleukin-6 mRNA. TNF mRNA half-life, measured after transcriptional arrest with actinomycin D, was reduced from 21.8 +/- 3.6 min in LPS-stimulated RAW 264.7 cells at 37 degrees C to 16.0 +/- 1.8 min at 40 degrees C (P < 0.03), but these cells at 40 degrees C did not alter transcription rate or TNF mRNA polysome association. TNF mRNA destabilization occurred at temperatures below the threshold (43 degrees C) for the generalized heat shock response in these cells. We conclude that heating macrophages to febrile-range temperatures attenuates sustained TNF expression by modulating posttranscriptional processing, including acceleration of TNF mRNA decay.
Suppression of a nonselective cation conductance by substance P in cochlear outer hair cells
Authors: Kakehata S. , Yamamoto T. , Takasaka T. , Akaike N.
Published: December 2017

Substance P (SP) hyperpolarizes outer hair cells (OHCs) of guinea pig cochlea. The cellular mechanisms of the SP response were investigated with the whole cell patch-clamp technique. SP induced outward currents in a dose-dependent manner at a holding potential of -60 mV in a concentration range between 3 x 10(-6) and 10(-4) M. SP decreased slope conductance between -60 and +20 mV. Ion substitutions in the external medium revealed that SP suppresses nonselective cation conductance with high permeability for Ca2+. The relative ion permeability of the channel modulated by SP was as follows: Ca2+ > Li+ approximately Cs+ approximately Na+ > Tris+. The potency of the agonist action was as follows: SP >> neurokinin A > neurokinin B. Peptide antagonists induced currents similar to those of SP. CP-96345, a selective nonpeptide antagonist for the neurokinin type 1 receptor, did not inhibit the SP-induced current. Intracellular dialysis of guanosine 5'-O-(2-thiodiphosphate) and pertussis toxin (PTX) suggests that a PTX-insensitive G protein is involved in the SP response. Neither the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid nor staurosporine (10(-6) M) affects the SP response. Local application of SP by a puffer pipette indicates that the SP receptors are distributed along the side of the OHC. These results suggest the possibility that the action of SP on the OHCs may not be mediated by the tachykinin receptors but rather by a tachykinin receptor-independent pathway. It is proposed that SP suppresses the nonselective cation conductance in the lateral wall of OHCs via a PTX-insensitive G protein.
Ion channel classes in purified olfactory cilia membranes: planar lipid bilayer studies
Authors: Jorquera O. , Latorre R. , Labarca P.
Published: December 2017

Ciliary membrane fragment fusion to planar lipid bilayers resulted in the insertion of four ion channel types. cAMP-activated, cation-selective channels could be detected only in the absence of Ca2+ and had a conductance of 23 pS. They exhibited an apparent dissociation constant (Kd) for the cyclic nucleotide of approximately 30 microM and an estimated permeability ratio (PNa/PK) of 2.4. The cAMP cation-selective channel coinserted with a K(+)-selective channel refractory to cAMP, Ca2+, and D-myo-inositol 1,4,5-trisphosphate. This K+ channel was voltage independent and exhibited open-conductance substates of 60 and 112 pS. cAMP was also found to modulate a novel K+ channel with a Kd = 140 microM. It displayed three nearly equally spaced open substates with conductances of 34, 80, and 130 pS. In the absence and in the presence of cAMP the probability of occurrence of the open substates was binomially distributed. A fourth channel type was a Ca(2+)-activated K+ channel with a conductance of 240 pS. It was blocked by charybdotoxin at nanomolar concentrations (Kd = 3 nM). These results add support to the idea that, besides cAMP-activated cation-selective channels, vertebrate chemosensory olfactory membranes possess an arrangement of ion channels.
Volume-associated osmolyte fluxes in cell lines with or without the anion exchanger
Authors: Sanchez-Olea R. , Fuller C. , Benos D. , Pasantes-Morales H.
Published: December 2017

To investigate the involvement of a red cell-type anion exchanger in the volume-sensitive amino acid release, the hyposmolarity-evoked release of D-[3H]aspartate and [3H]taurine was examined in three cell lines: 1) wild-type Chinese hamster ovary (CHO-K1) cells, expressing an anion exchanger activity (Cl-/SO4(2-)) functionally similar to the erythroid band 3; 2) a mutant CHO cell type (CHO 605) lacking this anion exchanger activity; and 3) 293 cells in which the Cl-/HCO3(-) anion exchanger is absent. All cell types accumulated D-[3H]aspartate and [3H]taurine under isosmotic conditions, and, similarly, in the three cell lines, cell swelling evoked by hyposmolarity induced a rapid and transient increase in the amino acid efflux. Blockers of the anion exchanger and/or Cl- channels [niflumic acid, dipyridamole, diphenylamine-2-carboxylate,5-nitro-2-(3-phenylpropylamino)-benzoi c acid, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid] were potent inhibitors of amino acid efflux in the three cell lines. 125I- efflux, used as a marker for Cl- fluxes, was also markedly increased in response to cell swelling in all cell lines, and this efflux was inhibited by the anion exchanger/Cl- channel blockers. These results do not support a role for an anion exchanger in the hyposmolarity-induced amino acid efflux and suggest that amino acids and Cl- may be transported by the same or a similar mechanism, presumably an anion channel-like structure.
Relationship between severity, necrosis, and apoptosis in five models of experimental acute pancreatitis
Authors: Kaiser A. M. , Saluja A. K. , Sengupta A. , Saluja M. , Steer M. L.
Published: December 2017

In an effort to elucidate factors that determine the severity of an attack of acute pancreatitis, we have quantitated the extent of necrosis and of apoptosis in five different models of experimental acute pancreatitis. Severe pancreatitis was induced by obstructing the opossum common bile-pancreatic duct, by administering to mice 12 hourly injections of a supramaximally stimulating dose of caerulein, and by feeding young female mice a choline-deficient, ethionine-supplemented diet. In each of these models of severe pancreatitis, marked necrosis but very little apoptosis was found. Mild pancreatitis was induced by obstructing the rat common bile-pancreatic duct and by infusing rats with a supramaximally stimulating dose of caerulein. In contrast to our findings in severe pancreatitis, mild pancreatitis was characterized by very little necrosis but a high degree of apoptosis. Our finding that the severity of acute pancreatitis is inversely related to the degree of apoptosis suggests that apoptosis may be a teleologically beneficial response to acinar cell injury in general and especially in acute pancreatitis.
Effects of magnesium on nitric oxide synthase activity in endothelial cells
Authors: Howard A. B. , Alexander R. W. , Taylor W. R.
Published: December 2017

Pages C612<C618: A. B. Howard, R. W. Alexander, and W. R. Taylor. “Effects of magnesium on nitric oxide synthase activity in endothelial cells.” Page C614, legend to Fig. 1: the open bars refer to A-23187-stimulated cells and the solid bars refer to cells under basal conditions, not the reverse as published.
MRF4, Myf-5, and myogenin mRNAs in the adaptive responses of mature rat muscle
Authors: Jacobs-El J. , Zhou M. -Y. , Russell B.
Published: December 2017

Pages C1045,C1052: J. Jacobs-El, M.-Y. Zhou, and B. Russell. “MRF4, Myf-5, and myogenin mRNAs in the adaptive responses of mature rat muscle.” Pages C1049 and C1051, Figs. 4 and 6 were inadvertently switched, although the legends as placed are correct. The correct Figs. 4 and 6 with their legends are as follows.

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Tachykinins activate nonselective cation currents in canine colonic myocytes
Authors: Lee H. K. , Shuttleworth C. W. , Sanders K. M.
Published: December 2017

The mechanism of tachykinin-induced excitation was studied in isolated colonic muscle cells and intact muscle strips. In whole cell voltage-clamp studies performed at 33 degrees C, neurokinin A (NKA) and substance P (SP) reduced L-type Ca2+ current. NKA and SP activated a cationic current that reversed near 0 mV. This current (INKA or ISP, respectively) had properties similar to the acetylcholine (ACh)-activated nonselective cation conductance (IACh), activated by muscarinic stimulation in other gastrointestinal smooth muscle cells. INKA and ISP were decreased when external Na+ was reduced. In contrast to IACh, INKA and ISP were not facilitated by increases in internal Ca2+, but little or no current was activated by these peptides when extracellular Ca2+ was low. INKA (10(-7) M) and ISP (10(-5) M) were blocked by Cd2+ (5 x 10(-4) M), quinine (10(-3) M), and the tachykinin-receptor antagonist [D-Pro2,D-Trp7,9]SP (10(-5) M). Current clamp recordings and intracellular recordings of intact tissues showed that NKA and SP depolarized the cell membrane, which is consistent with the activation of a nonselective cation conductance. These data suggest that a primary mechanism of the tachykinins is to activate a nonselective cation conductance that leads to depolarization. The increase in Ca2+ entry due to tachykinin stimulation appears to be secondary to the activation of the nonselective cation conductance.
Impaired development of interstitial cells and intestinal electrical rhythmicity in steel mutants
Authors: Ward S. M. , Burns A. J. , Torihashi S. , Harney S. C. , Sanders K. M.
Published: December 2017

Electrical rhythmicity in the gastrointestinal tract may originate in interstitial cells of Cajal (IC). Development of IC in the small intestine is linked to signaling via the tyrosine kinase receptor, c-kit. IC express c-kit protein, and disruption of c-kit signaling causes breakdown in IC networks and loss of slow waves. We tested whether mutations in steel factor, the ligand for c-kit, affect the development of IC networks. IC were found in the region of the myenteric plexus (IC-MY) in mice with steel mutations (i.e., Sl/Sld) at 5-10 days postpartum, but these cells formed an abnormal network. IC-MY were not observed in adult Sl/Sld animals. IC in the deep muscular plexus (IC-DMP) appeared normal in Sl/Sld animals. Electrical slow waves, normally present in the small intestine, were absent in Sl/Sld animals (10-30 days postpartum). Neural inputs were intact in Sl/Sld animals. Steel factor appears important for the development of certain classes of IC, and IC-MY appear to be involved in the generation of electrical rhythmicity in the small intestine.
Effects of acidosis on phosphorylation of phospholamban and troponin I in rat cardiac muscle
Authors: Mundina-Weilenmann C. , Vittone L. , Cingolani H. E. , Orchard C. H.
Published: December 2017

Acidosis inhibits Ca2+ transport by the sarcoplasmic reticulum of cardiac muscle and decreases the Ca2+ sensitivity of the contractile proteins, although the mechanisms underlying these changes are unclear. We have investigated the hypothesis that changes in the phosphorylation of the regulatory proteins phospholamban and troponin I might play a role in the acidosis-induced changes in the function of the sarcoplasmic reticulum and the myofilaments, respectively. Langendorff-perfused rat hearts were labeled with 32P and then perfused with either control (pH 7.4) or acid (pH 6.8) physiological salt solution, in both the absence and presence of isoproterenol. The incorporation of 32P into phospholamban and troponin I was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of sarcoplasmic reticulum and myofibrillar proteins, followed by autoradiography and liquid scintillation counting. The data show that acidosis has no effect on the phosphorylation of phospholamban in the absence of isoproterenol but that, in the presence of isoproterenol, acidosis increased the phosphorylation of phospholamban. However, acidosis increased the phosphorylation of troponin I, in both the absence and the presence of isoproterenol. Acidosis did not alter the adenosine 3',5'-cyclic monophosphate content of the hearts but did inhibit type 1 phosphatase. These data show that acidosis can alter the phosphorylation of these two proteins and suggest that these changes underlie, in part the changes observed in cardiac muscle during acidosis.
Growth hormone-releasing hormone augments voltage-gated Na+ current in cultured rat pituitary cells
Authors: Kato M.
Published: December 2017

The effect of human growth hormone-releasing hormone (hGHRH), a potent stimulator of adenylate cyclase in somatotrophs on the voltage-gated sodium current was determined by perforated patch clamp of cultured rat somatotrophs The amplitude of the voltage-gated sodium current was augmented by 65.3 +/- 20.6% (mean +/- SE, n = 7) by 10 nM hGHRH. This augmentation was reversibly blocked by 10 microM H-89 a specific inhibitor for adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. The membrane-permeant analogue of cAMP, dibutyryl cAMP (5 mM), also augmented the voltage-gated sodium current by 39.6 +/- 7.4% (n = 10). There were no effects of hGHRH or dibutyryl cAMP on steady-state inactivation of the sodium current. In contrast, in the whole cell configuration of patch clamp, no augmentation of the sodium current was observed by hGHRH or by the membrane-permeant analogue of cAMP. These results suggest that hGHRH augments the peak amplitude of the voltage-gated sodium current in rat somatotrophs via phosphorylation by cAMP-dependent protein kinase. For this augmentation, the intracellular environment must be kept relatively intact.
Induction of GLUT-1 mRNA in response to inhibition of oxidative phosphorylation: role of increased [Ca2+]i
Authors: Mitani Y. , Dubyak G. R. , Ismail-Beigi F.
Published: December 2017

Exposure of Clone 9 cells (a rat liver cell line expressing only the GLUT-1 isoform) to 5 mM azide or to 3 microM ionomycin for 12 h results in 3.7 +/- 0.3- and 4.9 +/- 0.4-fold increases in GLUT-1 mRNA content, respectively, suggesting the hypothesis that a rise in cytosolic free calcium concentration ([Ca2+]i) mediates the induction of GLUT-1 mRNA by azide. Five lines of evidence were employed to test this hypothesis. 1) Exposure of cells to 0-3 microM of ionomycin increased [Ca2+]i from 83 +/- 9 to 504 +/- 20 nM (half-maximal effect at 0.1 microM ionomycin), whereas half-maximal increase in GLUT-1 mRNA occurred at 1 microM ionomycin, with the increase in the mRNA being negligible at [Ca2+]i below 400 nM. Exposure of cells to 5 mM azide, however, increased [Ca2+]i to maximal value of 174 +/- 22 nM at 15 s, suggesting that the magnitude of the increase in [Ca2+]i by azide may not be adequate for the response. 2) The increase in GLUT-1 mRNA content by azide was fully preserved in cells preloaded with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). 3) GLUT-1 mRNA content increased within 30 min of exposure to ionomycin, whereas the mRNA increased after a "delay" period of 2 h in cells exposed to 5 mM azide. 4) A brief (2-min) rise in [Ca2+]i by ionomycin was sufficient to increase GLUT-1 mRNA content, whereas continuous exposure to azide for > 1 h was necessary for a subsequent induction of the mRNA. 5) Treatment with ionomycin, A-23187, and thapsigargin caused larger increases in glucose-regulated protein 78 and 94 and in 70-kDa heat shock protein mRNAs than in GLUT-1 mRNA, whereas treatment with azide resulted in greater induction of GLUT-1 mRNA. These results strongly suggest that, whereas increased [Ca2+]i enhances GLUT-1 mRNA expression and azide increases [Ca2+]i, the rise in [Ca2+]i does not mediate the induction of GLUT-1 mRNA in response to inhibition of oxidative phosphorylation.
Shortening heat in slow- and fast-twitch muscles of the rat
Authors: Holroyd S. M. , Gibbs C. L. , Luff A. R.
Published: December 2017

Shortening heat has been reported in several amphibian skeletal muscles. In this investigation, shortening heat has been investigated in both soleus and extensor digitorum longus (EDL) muscles of young rats. The procedure involved shortening the muscles through two different distances, at near maximum velocity and at the onset of a summated twitch from different initial lengths. At the end of the shortening period, the muscle contracted isometrically, and the stress and associated heat production were recorded. These heat-stress data were compared with heat-stress data of isometric twitches at different initial lengths. There was a parallel upward shift in energy output when shortening occurred, indicating the presence of a shortening heat. Shortening heat increased with the distance shortened in soleus, but this was not the case for EDL. The values for the shortening heat coefficient for both muscle types are slightly higher than those reported for amphibian skeletal muscle and suggest that shortening heat is a significant component of the energy output of mammalian skeletal muscle.
Creatine analogue beta-guanidinopropionic acid alters skeletal muscle AMP deaminase activity
Authors: Tullson P. C. , Rundell K. W. , Sabina R. L. , Terjung R. L.
Published: December 2017

Dietary supplementation of the creatine analogue beta-guanidinopropionic acid (beta-GPA) decreases in vitro skeletal muscle AMP deaminase (AMP-D) activity in rats. Downregulation of AMP-D activity was progressive and greater in fast-twitch muscles (70-80%) than in the slow-twitch soleus muscle (approximately 50%). The loss in AMP-D activity had little effect on inosine 5'-monophosphate accumulation in mixed-fiber muscle with intense tetanic contractions. In contrast, inosine 5'-monophosphate formation was evident earlier in fast-twitch red and white fiber sections of creatine-depleted animals during intense twitch contractions, indicating that fast-twitch muscle of beta-GPA-treated rats buffers decreases in the ATP/ADPfree ratio via deamination, even though AMP-D activity is less. Isoforms of skeletal muscle AMP-D mRNAs in mixed-fiber muscle were not altered by feeding beta-GPA for up to 9 wk. Creatine depletion did not alter total immunoreactivity; however, a redistribution of AMP-D immunoreactivity from primarily an approximately 80-kDa form toward lower apparent molecular mass species (approximately 60 and approximately 56 kDa) was observed. Posttranslational changes in AMP-D appear related to changes in activity.
Regulatory phosphorylation of the secretory Na-K-Cl cotransporter: modulation by cytoplasmic Cl
Authors: Lytle C. , Forbush B.
Published: December 2017

The effect of cytoplasmic Cl concentration ([Cl]i) on the activation state ([3H]benzmetanide binding rate) and phosphorylation state (32P incorporation) of the Na-K-Cl cotransporter was evaluated in secretory tubules isolated from the dogfish shark rectal gland. Reduction of [Cl]i at relatively constant cell volume (by removal of extracellular Cl or Na or by addition of bumetanide) increased cotransporter activation and phosphorylation. Raising extracellular K concentration ([K]o) from 4 to 80 mM, a maneuver that elevated [Cl]i above normal, reduced basal cotransport activity and rendered it entirely refractory to forskolin. High [K]o also blocked activation and phosphorylation in response to cell shrinkage, despite the fact that [Cl]i was already greatly elevated as a consequence of osmotic water loss. The phosphatase inhibitor calyculin A also promoted activation, but not in cells preexposed briefly to high [K]o. In summary, maneuvers than lower [Cl]i activate the cotransporter, whereas those that elevate [Cl]i (or prevent it from decreasing) block activation in response to secretory stimuli. Cell Cl appears to govern its own rate of entry via Na-K-Cl cotransport by impeding regulatory phosphorylation of the Na-K-Cl cotransport protein.
Recovery from NMDA-induced intracellular acidification is delayed and dependent on extracellular bicarbonate
Authors: Canzoniero L. M. , Sensi S. L. , Choi D. W.
Published: December 2017

A 30-s exposure to N-methyl-D-aspartate (NMDA) produced a dose-dependent and long-lasting (10-20 min) reduction in intracellular pH in cultured cortical neurons, detected by the fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. This intracellular acidification could be blocked by addition of the NMDA antagonist, D-(-)-2-amino-5-phosphonovalerate, or by removal of extracellular Ca2+. Removal of extracellular HCO3- markedly impaired recovery from NMDA-induced intracellular acidification. Recovery was also impaired when 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid or 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, inhibitors of HCO3- transport, were added to the cultures immediately after NMDA exposure. In contrast, the Na+/H+ exchange blocker, 5-(N-ethyl-N-isopropyl)amiloride, did not affect pH recovery. Removal of extracellular Cl- partially prevented pH recovery after NMDA stimulation. In addition, extracellular HCO3- increased intracellular Na+ after NMDA exposure, consistent with HCO3- activation of a Na(+)-dependent exchanger. These results demonstrate that stimulation of cortical neuronal NMDA receptors is followed by long-lasting intracellular acidification and that the presence of extracellular HCO3- is important in the subsequent recovery of normal intracellular pH, likely acting at least in part via the Na(+)-dependent Cl-/HCO3- exchanger.