Pacing rate, halothane, and BDM affect fura 2 reporting of [Ca2+]i in intact rat trabeculae

Effects of temperature and fatigue on the metabolism and swimming capacity of juvenile Chinese sturgeon (Acipenser sinensis)

Chinese sturgeon (Acipenser sinensis) is a critically endangered species. A flume-type respirometer, with video, was used to conduct two consecutive stepped velocity tests at 10, 15, 20, and 25 °C. Extent of recovery was measured after the 60-min recovery period between trials, and the recovery ratio for critical swimming speed (U _crit) averaged 91.88% across temperatures. Temperature (T) effects were determined by comparing U _crit, oxygen consumption rate (MO ₂), and tail beat frequency (TBF) for each temperature. Results from the two trials were compared to determine the effect of exercise. The U _crit occurring at 15 °C in both trials was significantly higher than that at 10 and 25 °C (p < 0.05). The U _crit was plotted as a function of T and curve-fitting allowed calculation of the optimal swimming temperature 3.28 BL/s at 15.96 °C (trial 1) and 2.98 BL/s at 15.85 °C (trial 2). In trial 1, MO ₂ increased rapidly with U, but then declined sharply as swimming speed approached U _crit. In trial 2, MO ₂ increased more slowly, but continuously, to U _crit. TBF was directly proportional to U and the slope (dTBF/dU) for trial 2 was significantly lower than that for trial 1. The inverse slope (tail beats per body length, TB/BL) is a measure of swimming efficiency and the significant difference in slopes implies that the exercise training provided by trial 1 led to a significant increase in swimming efficiency in trial 2.

Quantitative Ratiometric Ca2+ Imaging to Assess Cell Viability

Viability of cells is strongly related to their Ca²⁺ homeostasis. Ca²⁺ signal fluctuations can be on a slow time scale, e.g., in non-excitable cells, but also in the range of tens of milliseconds for excitable cells, such as nerve and muscle. Muscle fibers respond to electrical stimulation with Ca²⁺ transients that exceed their resting basal level about 100 times. Fluorescent Ca²⁺ dyes have become an indispensable means to monitor Ca²⁺ fluctuations in living cells online. Fluorescence intensity of such "environmental dyes" relies on a buffer-ligand interaction which is not only governed by laws of mass action but also by binding and unbinding kinetics that have to be considered for proper Ca²⁺ kinetics and amplitude validation. The concept of Ca²⁺ dyes including the different approaches using ratiometric and non-ratiometric dyes, the way to correctly choose dyes according to their low-/high-affinity properties and kinetics as well as staining techniques, and in situ calibration are reviewed and explained. We provide detailed protocols to apply ratiometric Fura-2 imaging of resting Ca²⁺ and Ca²⁺ fluctuations during field-stimulation in single isolated skeletal muscle cells and how to translate fluorescence intensities into absolute Ca²⁺ concentrations using appropriate calibration techniques.

Activation ofβ2-adrenergic receptor plays a pivotal role in generating the protective effect of ischemic preconditioning in rat hearts

BACKGROUND

Ischemic preconditioning (IPC) protects hearts against ischemia by reducing infarct size. However, IPC does not preserve cardiac function, such as left ventricular peak developed pressure (LVPDP). Moreover, IPC fails to protect the post-myocardial infarct (MI) heart.

DESIGN

Rat hearts were transfected with beta2-adrenergic receptor (B2AR) cDNA by the hemagglutinating virus of Japan-liposome method. After the gene transfer, the hearts were perfused in a Langendorff mode and preconditioned with two cycles of 5 min of ischemia and reperfusion. After 20 min of global ischemia, the hearts were reperfused under aerobic conditions for 90 min. LVPDP was measured as an indicator of the cardiac function.

RESULTS

LVPDP of ischemic hearts was well preserved by the combination treatment of IPC and gene transfer of B2AR, but not IPC or gene transfer of B2AR alone. Moreover, the treatment was beneficial to even the post-MI heart. On the contrary, gene transfer of beta-adrenergic receptor kinase 1 (BARK1) reduced the protective effect of IPC. We also found that the mRNA ratio of B2AR and BARK1 was well correlated with the preservation of the LVPDP.

CONCLUSIONS

The combination treatment of IPC and gene transfer of B2AR protects cardiac function against ischemia and it shows the beneficial effect also in post-MI hearts.

Sarcomere mechanics in uniform and nonuniform cardiac muscle: a link between pump function and arrhythmias

Starling's law and the end-systolic pressure-volume relationship (ESPVR) reflect the effect of sarcomere length (SL) on the development of stress (sigma) and shortening by myocytes in the uniform ventricle. We show here that tetanic contractions of rat cardiac trabeculae exhibit a sigma-SL relationship at saturating [Ca2+] that depends on sarcomere geometry in a manner similar to that of skeletal sarcomeres and the existence of opposing forces in cardiac muscle shortened below slack length. The sigma-SL -[Ca2+](free) relationships (sigma-SL-Ca relationships) at submaximal [Ca2+] in intact and skinned trabeculae were similar, although the sensitivity for Ca2+ of intact muscle was higher. We analyzed the mechanisms underlying the sigma-SL-Ca relationship by using a kinetic model assuming that the rates of Tn-C Ca2+ binding and/or cross-bridge (XB) cycling are determined by either the SL, [Ca2+], or sigma. We analyzed the correlation between the model results and steady-state sigma measurements at varied SL at [Ca2+] from skinned rat cardiac trabeculae to test the hypotheses that the dominant feedback mechanism is SL-, sigma-, or [Ca2+]-dependent, and that the feedback mechanism regulates Tn-C Ca2+ affinity, XB kinetics, or the unitary XB force. The analysis strongly suggests that the feedback of the number of strong XBs to cardiac Tn-C Ca2+ affinity is the dominant mechanism regulating XB recruitment. Using this concept in a model of twitch-sigma accurately reproduced the sigma-SL-Ca relationship and the time courses of twitch sigma and the intracellular [Ca2+]i. The foregoing concept has equally important repercussions for the nonuniformly contracting heart, in which arrhythmogenic Ca2+ waves arise from weakened areas in the cardiac muscle. These Ca2+ waves can reversibly be induced with nonuniform excitation-contraction coupling (ECC) by the cycle of stretch and release in the border zone between the damaged and intact regions. Stimulus trains induced propagating Ca2+ waves and reversibly induced arrhythmias. We hypothesize that rapid force loss by the sarcomeres in the border zone during relaxation causes Ca2+ release from Tn-C and initiates Ca2+ waves propagated by the sarcoplasmic reticulum (SR). Modeling of the response of the cardiac twitch to rapid force changes using the feedback concept uniquely predicts the occurrence of [Ca2+]i transients as a result of accelerated Ca2+ dissociation from Tn-C. These results are consistent with the hypothesis that a force feedback to Ca2+ binding by Tn-C is responsible for Starling's law and the ESPVR in the uniform myocardium and leads to a surge of Ca2+ released by the myofilaments during relaxation in the nonuniform myocardium, which initiates arrhythmogenic propagating Ca2+ release by the SR.

Effect of tumor necrosis factor α on electrically induced calcium transients elicited in C2C12 skeletal myotubes

Diseases involving chronic inflammation can lead to prolonged exposure of skeletal muscle to inflammatory cytokines such as tumor necrosis factor alpha (TNFalpha), which may contribute to the skeletal muscle weakness seen in these conditions. In this study we examined the effect of a prolonged exposure to TNFalpha on intracellular Ca(2+) transients elicited in skeletal C(2)C(12) myotubes. A 48-h exposure to TNFalpha (10 ng/mL) significantly reduced the peaks, time to peak, and rate of Ca(2+) decay of electrically induced Ca(2+) transients elicited in C(2)C(12) skeletal myotubes. TNFalpha exposure had no significant effect on the resting Ca(2+) levels. The results of this study indicate that prolonged exposure to TNFalpha decreases sarcoplasmic reticulum Ca(2+) release in cultured skeletal muscle cells. This altered Ca(2+) release could contribute to the muscle weakness found in conditions involving chronic inflammation.

Spatial Nonuniformity of Contraction Causes Arrhythmogenic Ca2+Waves in Rat Cardiac Muscle

Landesberg and Sideman's four state model of the cardiac cross-bridge (XB) hypothesizes a feedback of force development to Ca(2+) binding by troponin C (TnC). We have further modeled this behavior and observed that the force (F)-Ca(2+) relationship as well as the F-sarcomere length (SL) relationship and the time course of F and Ca(2+) transients in cardiac muscle can be reproduced faithfully by a single effect of F on deformation of the TnC-Ca complex and, thereby, on the dissociation rate of Ca(2+). Furthermore, this feedback predicts that rapid decline of F in the activated sarcomere causes release of Ca(2+) from TnC-Ca(2+), which is sufficient to initiate arrhythmogenic Ca(2+) release from the sarcoplasmic reticulum (SR). This work investigated the initiation of Ca(2+) waves underlying triggered propagated contractions (TPCs) in rat cardiac trabeculae under conditions that simulate functional nonuniformity caused by mechanical or ischemic local damage of the myocardium. A mechanical discontinuity along the trabeculae was created by exposing the preparation to a small constant flow jet of solution that reduces excitation-contraction coupling in myocytes within that segment. Force was measured, and SL as well as [Ca(2+)](i) were measured regionally. When the jet contained caffeine, 2,3-butanedione monoxime or low-[Ca(2+)], muscle-twitch F decreased and the sarcomeres in the exposed segment were stretched by shortening the normal regions outside the jet. During relaxation, the sarcomeres in the exposed segment shortened rapidly. Short trains of stimulation at 2.5 Hz reproducibly caused Ca(2+) waves to rise from the borders exposed to the jet. Ca(2+) waves started during F relaxation of the last stimulated twitch and propagated into segments both inside and outside of the jet. Arrhythmias, in the form of nondriven rhythmic activity, were triggered when the amplitude of the Ca(2+) wave increased by raising [Ca(2+)](o). The arrhythmias disappeared when the muscle uniformity was restored by turning the jet off. These results show that nonuniform contraction can cause Ca(2+) waves underlying TPCs, and suggest that Ca(2+) dissociated from myofilaments plays an important role in the initiation of arrhythmogenic Ca(2+) waves.

Enhanced response to caffeine and 4-chloro-m-cresol in malignant hyperthermia-susceptible muscle is related in part to chronically elevated resting [Ca2+]i

Malignant hyperthermia (MH) is a potentially fatal pharmacogenetic syndrome caused by exposure to halogenated volatile anesthetics and/or depolarizing muscle relaxants. We have measured intracellular Ca(2+) concentration ([Ca(2+)](i)) using double-barreled, Ca(2+)-selective microelectrodes in myoballs prepared from skeletal muscle of MH-susceptible (MHS) and MH-nonsusceptible (MHN) swine. Resting [Ca(2+)](i) was approximately twofold in MHS compared with MHN quiescent myoballs (232 +/- 35 vs. 112 +/- 11 nM). Treatment of myoballs with caffeine or 4-chloro-m-cresol (4-CmC) produced an elevation in [Ca(2+)](i) in both groups; however, the concentration required to cause a rise in [Ca(2+)](i) elevation was four times lower in MHS than in MHN skeletal muscle cells. Incubation of MHS cells with the fast-complexing Ca(2+) buffer BAPTA reduced [Ca(2+)](i), raised the concentration of caffeine and 4-CmC required to cause an elevation of [Ca(2+)](i), and reduced the amount of Ca(2+) release associated with exposure to any given concentration of caffeine or 4-CmC to MHN levels. These results suggest that the differences in the response of MHS skeletal myoballs to caffeine and 4-CmC may be mediated at least in part by the chronic high resting [Ca(2+)](i) levels in these cells.

Cystic fibrosis transmembrane conductance regulator in human and mouse red blood cell membranes and its interaction with ecto-apyrase

Elevated blood ATP and increased red blood cell (RBC) ATP transport is associated with cystic fibrosis (CF). In this report, we demonstrate the presence of the wild-type and the DeltaF508 mutant form of the CF transmembrane conductance regulator protein in RBC membranes and its putative interaction with ecto-apyrase, an ATP hydrolyzing enzyme also present in the RBC membrane. RBC membranes of control and DeltaF508 individuals and of wild-type and CF transmembrane conductance regulator-knockout mice were examined by immunoblot using several antibodies directed against different epitopes of this protein. These experiments indicated that human RBC membranes contain comparable amounts of the wild-type CF transmembrane conductance regulator protein and the DeltaF508 mutant form of the protein, respectively. CF transmembrane conductance regulator protein was also detected in wild-type mouse RBC membranes but not in the gene knockout mouse RBC membranes. Antibodies directed against ecto-apyrase co-immunoprecipitated CF transmembrane conductance regulator protein of human RBC membranes indicating a physical interaction between these two membrane proteins consistent with ATP transport and extracellular hydrolysis. We conclude that RBCs are a significant repository of CF transmembrane conductance regulator protein and should provide a novel system for evaluating its expression and function.

Age Increases Expression and Receptor-Mediated Activation of Gαi in Human Atria

Recently, we demonstrated that beta2AR and several other Galphas-coupled receptors in human atria also couple to Galphai, a G protein that inhibits adenylyl cyclase (AC). The present study was undertaken to determine whether age increases expression of Galphai in human atrium, and more specifically whether it results in an increase in receptor-mediated activation of Galphai. Right atrial appendages were obtained from 14 mature adult (40-55 years) and 14 elderly (71-79 years) patients undergoing cardiac surgery. Immunoblotting of atrial membranes indicates that elderly atria have 82 +/- 18% more Galphai2 than atria from mature adults (P < 0.002); this increase in Galphai with age is confirmed by pertussis toxin-catalyzed ADP-ribosylation as well as by photoaffinity labeling with [32P]azidoanilido-GTP. We also find that receptor-mediated activation of Galphai is greater in elderly atria and that both basal and receptor-mediated AC activities decrease in elderly atria. These decreases in AC activity can be reversed by disabling Galphai with pertussis toxin, indicating that the age-dependent increases in Galphai expression and activation have functional consequences. Because beta2ARs in human atria mediate contractility through cAMP-mediated phosphorylation of phospholamban, we conclude that an age-induced increase in Galphai may have a role in depressing cardiac function in aged human atria.

Stimulation of beta 2-adrenergic receptor increases cystic fibrosis transmembrane conductance regulator expression in human airway epithelial cells through a cAMP/protein kinase A-independent pathway

PSD-95/Dlg-A/ZO-1 (PDZ) domains play an essential role in determining cell polarity. The Na(+)/H(+) exchanger regulatory factor (NHERF), also known as EBP50, contains two PDZ domains that mediate the assembly of transmembrane and cytosolic proteins into functional signal transduction complexes. Moreover, it has been shown that cystic fibrosis transmembrane conductance regulator (CFTR) and beta(2)-adrenergic receptor (beta(2)AR) bind equally well to the PDZ1 domain of EBP50. We hypothesized that beta(2)AR activation may regulate CFTR protein expression. To verify this, we evaluated the effects of a pharmacologically relevant concentration of salmeterol (2.10(-7) m), a long acting beta(2)AR agonist, on CFTR expression in primary human airway epithelial cells (HAEC). beta(2)AR stimulation induced a time-dependent increase in apical CFTR protein expression, with a maximal response reached after treatment for 24 h. This effect was post-transcriptional, dependent upon the beta(2)AR agonist binding to beta(2)AR and independent of the known beta(2)AR agonist-mediated cAMP/PKA pathway. We demonstrated by immunohistochemistry that CFTR, beta(2)AR, and EBP50 localize to the apical membrane of HAEC. Analyses of anti-EBP50 protein immunoprecipitate showed that salmeterol induced an increase in the amount of CFTR that binds to EBP50. These data suggest that beta(2)AR activation regulates the association of CFTR with EBP50 in polarized HAEC.

Reduced contraction strength with increased intracellular [Ca2+] in left ventricular trabeculae from failing rat hearts

Intracellular calcium ([Ca2+](i)) and isometric force were measured in left ventricular (LV) trabeculae from spontaneously hypertensive rats (SHR) with failing hearts and normotensive Wistar-Kyoto (WKY) controls. At a physiological stimulation frequency (5 Hz), and at 37 degrees C, the peak stress of SHR trabeculae was significantly (P < or = 0.05) reduced compared to WKY (8 +/- 1 mN mm(-2) (n = 8) vs. 21 +/- 5 mN mm(-2) (n = 8), respectively). No differences between strains in either the time-to-peak stress, or the time from peak to 50 % relaxation were detected. Measurements using fura-2 showed that in the SHR both the peak of the Ca2+ transient and the resting [Ca2+](i) were increased compared to WKY (peak: 0.69 +/- 0.08 vs. 0.51 +/- 0.08 microM(P < or = 0.1) and resting: 0.19 +/- 0.02 vs. 0.09 +/- 0.02 microM(P < or = 0.05), SHR vs. WKY, respectively). The decay of the Ca2+ transient was prolonged in SHR, with time constants of: 0.063 +/- 0.002 vs. 0.052 +/- 0.003 s (SHR vs. WKY, respectively). Similar results were obtained at 1 Hz stimulation, and for [Ca2+ ](o) between 0.5 and 5 mM. The decay of the caffeine-evoked Ca2+ transient was slower in SHR (9.8 +/- 0.7 s (n = 8) vs. 7.7 +/- 0.2 s (n = 8) in WKY), but this difference was removed by use of the SL Ca2+ -ATPase inhibitor carboxyeosin. Histological examination of transverse sections showed that the fractional content of perimysial collagen was increased in SHR compared to WKY (18.0 +/- 4.6 % (n = 10) vs. 2.9 +/- 0.9 % (n = 11) SHR vs. WKY, respectively). Our results show that differences in the amplitude and the time course of the Ca2+ transient between SHR and WKY do not explain the reduced contractile performance of SHR myocardium per se. Rather, we suggest that, in this animal model of heart failure, contractile function is compromised by increased collagen, and its three-dimensional organisation, and not by reduced availability of intracellular Ca2+.

Halothane, isoflurane and sevoflurane inhibit NADH:ubiquinone oxidoreductase (complex I) of cardiac mitochondria

We have investigated the effects of volatile anaesthetics on electron transport chain activity in the mammalian heart. Halothane, isoflurane and sevoflurane reversibly increased NADH fluorescence (autofluorescence) in intact ventricular myocytes of guinea-pig, suggesting that NADH oxidation was impaired. Using pig heart submitochondrial particles we found that the anaesthetics dose-dependently inhibited NADH oxidation in the order: halothane > isoflurane = sevoflurane. Succinate oxidation was unaffected by either isoflurane or sevoflurane, indicating that these agents selectively inhibit complex I (NADH:ubiquinone oxidoreductase). In addition to inhibiting NADH oxidation, halothane also inhibited succinate oxidation (and succinate dehydrogenase), albeit to a lesser extent. To test the hypothesis that complex I is a target of volatile anaesthetics, we examined the effects of these agents on NADH:ubiquinone oxidoreductase (EC 1.6.99.3) activity using the ubiquinone analogue DBQ (decylubiquinone) as substrate. Halothane, isoflurane and sevoflurane dose-dependently inhibited NADH:DBQ oxidoreductase activity. Unlike the classical inhibitor rotenone, none of the anaesthetics completely inhibited enzyme activity at high concentration, suggesting that these agents bind weakly to the 'hydrophobic inhibitory site' of complex I. In conclusion, halothane, isoflurane and sevoflurane inhibit complex I (NADH:ubiquinone oxidoreductase) of the electron transport chain. At concentrations of approximately 2 MAC (minimal alveolar concentration), the activity of NADH:ubiquinone oxidoreductase was reduced by about 20 % in the presence of halothane or isoflurane, and by about 10 % in the presence of sevoflurane. These inhibitory effects are unlikely to compromise cardiac performance at usual clinical concentrations, but may contribute to the mechanism by which volatile anaesthetics induce pharmacological preconditioning.

Monitoring intracellular pH changes in response to osmotic stress and membrane transport activity using 5-chloromethylfluorescein

Intracellular free H+ concentration (pHi) responds to numerous extracellular stimuli. The use of fluorescent indicator dyes to measure pHi is strongly influenced by the ability of target cells to retain activated dye within the cytoplasmic compartment. Here, 3 pH-sensitive indicator dye - acetoxymethyl (AM) esters of SNARF-1 and BCECF, and the thiol-reactive 5-chloromethyfluorescein (CMFDA) - were examined for monitoring pHi. The stability of pH measurements was strongly affected by temperature, cell type, indicator dye, and use of transport inhibitors to prevent dye export. Cellular retention of CMFDA, which forms covalent complexes, was sufficient to permit monitoring of transient pHi changes over extended time periods in a multi-well plate assay format. In human embryonic kidney (HEK293) and Chinese hamster ovary (CHO) cells, increasing osmotic pressure caused a significant rise in pHi. In contrast, activation of native or transfected beta-adrenergic, cholinergic, and d and m opioid receptors did not measurably affect pHi in HEK293 cells. Decreases in pHi were observed in CHO cells expressing the human H+/peptide transporter PEPT1 upon addition of dipeptide substrates. The use of CMFDA in multi-well formats should facilitate study of osmotic and transport activity and screening for drugs that affect pHi.

Age increases cardiac Galpha(i2) expression, resulting in enhanced coupling to G protein-coupled receptors

Cardiac G protein-coupled receptors that function through stimulatory G protein Galpha(s), such as beta(1)- and beta(2)-adrenergic receptors (beta(1)ARs and beta(2)ARs), play a key role in cardiac contractility. Recent data indicate that several Galpha(s)-coupled receptors in heart also activate Galpha(i), including beta(2)ARs (but not beta(1)ARs). Coupling of cardiac beta(2)ARs to Galpha(i) inhibits adenylyl cyclase and opposes beta(1)AR-mediated apoptosis. Dual coupling of beta(2)AR to both Galpha(s) and Galpha(i) is likely to alter beta(2)AR function in disease, such as congestive heart failure in which Galpha(i) levels are increased. Indeed, heart failure is characterized by reduced responsiveness of betaARs. Cardiac betaAR-responsiveness is also decreased with aging. However, whether age increases cardiac Galpha(i) has been controversial, with some studies reporting an increase and others reporting no change. The present study examines Galpha(i) in left ventricular membranes from young and old Fisher 344 rats by employing a comprehensive battery of biochemical assays. Immunoblotting reveals significant increases with age in left ventricular Galpha(i2), but no changes in Galpha(i3), Galpha(o), Galpha(s), Gbeta(1), or Gbeta(2). Aging also increases ADP-ribosylation of pertussis toxin-sensitive G proteins. Consistent with these results, basal as well as receptor-mediated incorporation of photoaffinity label [(32)P]azidoanilido-GTP indicates higher amounts of Galpha(i2) in older left ventricular membranes. Moreover, both basal and receptor-mediated adenylyl cyclase activities are lower in left ventricular membranes from older rats, and disabling of Galpha(i) with pertussis toxin increases both basal and receptor-stimulated adenylyl cyclase activity. Finally, age produces small but significant increases in muscarinic potency for the inhibition of both beta(1)AR- and beta(2)AR-stimulated adenylyl cyclase activity. The present study establishes that Galpha(i2) increases with age and provides data indicating that this increase dampens adenylyl cyclase activity.

Compartmentation of G protein-coupled signaling pathways in cardiac myocytes

There is a large body of functional data that supports the existence of subcellular compartmentation of the components of cyclic AMP action in the heart. Data from isolated perfused hearts and from purified ventricular myocytes imply a fixed and hormone-specific spatial relationship amongst components of cyclic AMP synthesis, response, and degradation. Available data demonstrate that within a cardiac myocyte, not all cyclic AMP gains access to all cyclic AMP-dependent protein kinase (PKA), that not all PKA interacts with all possible cellular substrates of PKA, and that only a subset of the myocyte's phosphodiesterases (PDEs) may degrade cyclic AMP after a given synthetic stimulus. Molecular mechanisms contributing to compartmentation are being discovered: localization of receptors, G proteins, and adenylyl cyclases in caveolar versus noncaveolar regions of the sarcolemma; localization of PKA by A-kinase anchoring proteins; localization of PKA substrates, PDE isoforms, and phosphoprotein phosphatases in discrete subcellular regions; and differential regulation of multiple isoforms of adenylyl cyclase, phosphoprotein phosphatase, and PDE in distinct subcellular compartments.

Control of cystic fibrosis transmembrane conductance regulator expression by BAP31

Expression of the cystic fibrosis transmembrane conductance regulator (CFTR) is stringently controlled by molecular chaperones participating in formation of the quality control system. It has been shown that about 75% of all CFTR protein and close to 100% of the [DeltaPhe(508)] CFTR variant are rapidly degraded before leaving the endoplasmic reticulum (ER). B cell antigen receptor-associated proteins (BAPs) are ubiquitously expressed integral membrane proteins that may control association with the cytoskeleton, vesicular transport, or retrograde transport from the cis Golgi to the ER. The present study delivers evidence for cytosolic co-localization of both BAP31 and CFTR and for the control of expression of recombinant CFTR in Chinese hamster ovary (CHO) cells and Xenopus oocytes by BAP31. Antisense inhibition of BAP31 in various cell types increased expression of both wild-type CFTR and [DeltaPhe(508)]CFTR and enabled cAMP-activated Cl(-) currents in [DeltaPhe(508)]CFTR-expressing CHO cells. Coexpression of CFTR together with BAP31 attenuated cAMP-activated Cl(-) currents in Xenopus oocytes. These data therefore suggest association of BAP31 with CFTR that may control maturation or trafficking of CFTR and thus expression in the plasma membrane.

Measurements of intracellular free calcium concentration in biological systems

Intracellular calcium plays a role in signaling and as a second messenger in many types of cells and its concentration is closely regulated in cells. Two techniques for measuring intracellular free calcium are using fluorescent ratiometric and nonratiometric probes are described in this unit: fluorescent spectroscopy to measure calcium concentrations in a suspension of cells and fluorescent digital imaging microscopy (FDIM) to measure calcium concentrations in plated cells.

Effect of transient stretch on intracellular Ca2+ during triggered propagated contractions in intact trabeculae

Transient stretch of cardiac muscle during a twitch contraction may dissociate Ca2+ from myofilaments into the cytosol at the moment of quick release of the muscle. We studied the effect of stretch and quick release of trabeculae on changes in intracellular Ca2+ ([Ca2+]i) during triggered propagated contractions (TPCs). Trabeculae were dissected from the right ventricle of 9 rat hearts. [Ca2+]i was measured using electrophoretically injected fura-2. Force was measured using a silicon strain gauge and sarcomere length was measured using laser diffraction techniques. Reproducible TPCs (n = 13) were induced by trains of electrical stimuli (378 ± 19 ms interval) for 7.5 s at [Ca2+]o of 2.0 mM (27.9 ± 0.2°C). The latency of the TPC force and the underlying increase in [Ca2+]i was calculated from the time (TimeF) between the last stimulus and the peak of TPC force (PeakF), or the time (TimeCa) between the last stimulus and the peak of the increase in [Ca2+]i during the TPCs (PeakCa). As a result of a 10% increase in muscle length for 150-200 ms during the last stimulated twitches, TimeF and TimeCa decreased and PeakF and PeakCa increased significantly (n = 13). In addition, transient stretch sometimes induced a twitch contraction subsequent to the accelerated TPC and its underlying increase in [Ca2+]i. These results suggest that Ca2+ binding and dissociation from the myofilaments by the stretch and quick release of muscle may modulate the TPC force and the underlying increases in [Ca2+]i and play an important role in the induction of arrhythmias.Key words: rat cardiac trabeculae, stretch, calcium transients.

2,3-butanedione monoxime unmasks Ca(2+)-induced NADH formation and inhibits electron transport in rat hearts

We used 2,3-butanedione monoxime (BDM) to suppress work by the perfused rat heart and to investigate the effects of calcium on NADH production and tissue energetics. Hearts were perfused with buffer containing BDM and elevated perfusate calcium to maintain the rates of cardiac work and oxygen consumption at levels similar to those of control perfused hearts. BDM plus calcium hearts displayed higher levels of NADH surface fluorescence, indicating calcium activation of mitochondrial dehydrogenases. These hearts, however, displayed 20% lower phosphocreatine levels. BDM suppressed the rates of state 3 respiration of isolated mitochondria. Uncoupled respiration was suppressed to a lesser degree, and the state 4 respiration rates were not affected. Double-inhibitor experiments with liver mitochondria using BDM and carboxyatractyloside (CAT) were used to identify the site of inhibition. BDM at low levels (0-5 mM) suppressed respiration. In the presence of CAT at levels that inhibit respiration by 60%, low levels of BDM were without effect. Because these effects were not additive, BDM does not inhibit adenine nucleotide transport. This was supported by an assay of adenine nucleotide transport in liver mitochondria. BDM did not inhibit ATP hydrolysis by submitochondrial particles but strongly suppressed reversed electron transport from succinate to NAD(+). Oxidation of NADH by submitochondrial particles was inhibited by BDM but oxidation of succinate was not. We conclude that BDM inhibits electron transport at site 1.

A cystic fibrosis tracheal gland cell line, CF-KM4. Correction by adenovirus-mediated CFTR gene transfer

Human tracheal gland serous (HTGS) cells are now considered one principal pulmonary target for the gene therapy of cystic fibrosis (CF). We developed a CF tracheal gland serous cell line, CF-KM4, obtained by the transformation of primary cultures of CF tracheal gland serous cells homozygous for the DeltaF508 mutation by using the wild-type SV40 virus. This cell line retained epithelial and secretory features of the native CF-HTGS cells in primary culture, namely, presence of cytokeratin, constitutive secretion of secretory leukocyte proteinase inhibitor, absence of responsiveness to carbachol and isoproterenol, and defective cyclic adenosine monophosphate-dependent chloride channel activity. Adenovirus-mediated CF transmembrane conductance regulator (CFTR) gene transfer into CF-KM4 cells corrected the defective chloride channel activity as well as the responsiveness to adrenergic and cholinergic agonists. In contrast, control transfection using adenovirus-mediated beta-galactosidase gene transfer was totally ineffective. In conclusion, these results present a stable CF tracheal gland cell line that has retained its epithelial and CF-specific defective secretory characteristics which are corrected after CFTR gene transfer. This cell line therefore appears to be a useful tool for large-scale molecular and cellular pharmacologic investigations designed to test potential therapies of the disease CF.

Effects of isoflurane on [Ca2+]i, SR Ca2+ content, and twitch force in intact trabeculae

The goal was to test whether isoflurane exerts its depressant effect on the heart by mainly affecting the intracellular Ca2+ transient [Ca2+]i. Intact rat ventricular trabeculae, paced at 0.5 Hz and 30 degreesC with extracellular [Ca2+] ([Ca2+]o) of 2 mM, were used. The [Ca2+]i was monitored using fura 2 injected into the myoplasm. The sarcoplasmic reticulum (SR) Ca2+ content was estimated using rapid cooling with or without caffeine to induce Ca2+ release and contracture. A plot of peak twitch force versus peak [Ca2+]i transient with increasing isoflurane concentration declines linearly so that a 56% reduction in the peak [Ca2+]i transient would abolish twitch force. This relationship is intermediate between those obtained with lowering [Ca2+]o, which depresses twitch force through a reduction of the [Ca2+]i transient, and adding 2,3-butanedione monoxime, which reduces the responsiveness of the contractile system to [Ca2+]i. The isoflurane effect is different from that of halothane with respect to both the above relationship and the rapid-cooling response. Isoflurane abolishes the ability of rapid cooling to liberate Ca2+ from the SR.

Ca2+ regulates the kinetics of tension development in intact cardiac muscle

The goal of this study was to determine whether Ca2+ plays a role in regulating tension development kinetics in intact cardiac muscle. In cardiac muscle, this fundamental issue of Ca2+ regulation has been controversial. The approach was to induce steady-state tetanic contractions of intact right ventricular trabeculae from rat hearts at varying external Ca2+ concentrations ([Ca2+]) at 22 degreesC. During tetani, cross bridges were mechanically disrupted and the kinetics of tension redevelopment were assessed from the rate constant of exponential tension redevelopment (ktr). There was a relationship between ktr and external [Ca2+] that was similar in form to the relationship between tension and [Ca2+]. Thus a close relationship also existed between ktr and tension (r = 0.88; P < 0. 001); whereas at maximal tetanic tension (saturating cytosolic [Ca2+]), ktr was 16.4 +/- 2.2 s-1 (mean +/- SE, n = 7), at zero tension (low cytosolic [Ca2+]), ktr extrapolated to 20% of maximum (3.3 +/- 0.7 s-1). Qualitatively similar results were obtained using different mechanical protocols to disrupt cross bridges. These data demonstrate that tension redevelopment kinetics in intact cardiac muscle are influenced by the level of Ca2+ activation. These findings contrast with the findings of one previous study of intact cardiac muscle. Activation dependence of tension development kinetics may play an important role in determining the rate and extent of myocardial tension rise during the cardiac cycle in vivo.

Basis for late rise in fura 2 R signal reporting [Ca2+]i during relaxation in intact rat ventricular trabeculae

Intact rat ventricular trabeculae were injected with the salt form of fura 2, and the fura 2 ratio signal (R) was used to report intracellular Ca2+ concentration ([Ca2+]i). The fixed end relaxation phase of a twitch is associated with a slowing of the decay of the R signal, or even a reversal, to form a distinct bump, indicating a transient rise in [Ca2+]i. The bump is most prominent at 30 degrees C, and motion artifact is not its cause. Increasing doses of 2,3-butanedione monoxime caused progressive attenuation of the twitch and bump. Increasing the bathing Ca2+ concentration potentiated the twitch and enhanced the bump. Imposed muscle shortening during relaxation caused a much quicker force decline, and this led to the appearance of a much more prominent associated bump. The amplitude of the bump depends on the amplitude of twitch force and the rate of relaxation. These findings can be explained, as in skeletal muscle, by making cross-bridge attachment and Ca2+ binding to troponin C strongly cooperative; therefore, the bump during fast relaxation is produced by a reversal of this cooperatively, leading to rapid dissociation of Ca2+ from troponin C into the myoplasm.

Effects of halothane on [Ca2+]i transient, SR Ca2+ content, and force in intact rat heart trabeculae

The goal of this study was to test whether the well-known cardiodepressant effect of halothane is caused mainly by depression of the transient increase in intracellular Ca2+ concentration ([Ca2+]i) during a twitch. Intact rat ventricular trabeculae, paced at 0.5 Hz and 30 degrees C with a bathing extracellular Ca2+ concentration ([Ca2+]o) of 2 mM, were used. The [Ca2+]i was monitored with the use of fura 2 injected into the myoplasm. The sarcoplasmic reticulum (SR) Ca2+ content was estimated with the use of rapid cooling (RC)-induced contracture force and Ca2+ release. The relationship of the peak [Ca2+]i transient versus peak twitch force obtained with halothane is intermediate between those obtained with lowered [Ca2+]o and varying doses of 2,3-butanedione monoxime. The data indicate that the negative inotropic action of halothane at low (0.18 mM) dose is mainly achieved by reduction in the Ca2+ sensitivity of the contractile apparatus, whereas, at high dose (0.55 mM), halothane acts both by reducing the [Ca2+]i transient and the Ca2+ sensitivity of the contractile system. At moderate (0.37 mM) dose, the effects were midway between low and high doses. With the use of RC contracture force alone, the reduction of SR Ca2+ content caused by halothane is overestimated.