Biomedical subjects

Kuo-Hsing Kuo

Publications and source records attributed to Kuo-Hsing Kuo.

At least 19 recordsLinked to original sources

PubMed2006

Acetylcholine-induced asynchronous calcium waves in intact human bronchial muscle bundle.

Calcium (Ca2+) is an important activator of the contractile machinery in airway smooth muscle (ASM). While agonist-induced Ca2+ signals are well characterized in animal ASM, little is known about what occurs in adult human ASM. In this study, we examined the Ca2+ signal elicited by acetylcholine (ACh) in smooth muscle cells of the intact human bronchial muscle strips obtained from fresh surgical specimens in relation to muscle contraction. We found that ACh induces repetitive Ca2+ waves that spread along the longitudinal axis of individual cells in the intact human bronchial smooth muscle strips. These Ca2+ waves display no apparent synchronization between neighboring cells, and their generation precedes force development. Comparison of the ACh concentration dependence of tissue contraction and selected parameters of the asynchronous Ca2+ waves (ACW) reveals that the graded force generation by ACh-stimulated human bronchial muscle strips is achieved by differential recruitment of cells to initiate Ca2+ waves and by enhancement of the frequency of ACW once the cells are recruited. Furthermore, pharmacologic characterization shows that the ACW are produced by repetitive cycles of SR Ca2+ release via ryanodine-sensitive channels followed by SR Ca2+ reuptake by sarco(endo)plasmic reticulum Ca2+ ATPase. Extracellular Ca2+ entry involving receptor-operated channels/store-operated channels, reverse-mode Na+/Ca2+ exchange, and to a lesser extent L-type voltage-gated Ca2+ channels is required to maintain the ACW. These findings for the first time demonstrate the occurrence and the role of ACW in excitation-contraction coupling in adult human ASM.

Acetylcholine↗

PubMed2006

Acute intralipid infusion reduces cardiac luminal lipoprotein lipase but recruits additional enzyme from cardiomyocytes.

OBJECTIVE: Lipoprotein lipase (LPL) metabolizes the triglyceride (TG) core of lipoproteins. We evaluated whether circulating lipids can regulate LPL by influencing the transfer of enzyme from the myocyte to the endothelial lumen. METHODS: Acute intralipid (IL, 10% and 20%) infusion was performed in male Wistar rats. After 3 h, insulin resistance was assessed using a euglycemic hyperinsulinemic clamp. Cardiac LPL activity was determined by retrogradely perfusing the hearts with heparin. Immunogold electron microscopy visualized LPL, and heparanase was detected by immunofluorescence. Cardiac myocytes were also isolated, and heparin-releasable LPL activity was measured. RESULTS: IL infusion increased both plasma and cardiac lipids. Circulating basal plasma LPL activity increased for the duration of the infusion. Compared to control (CON) hearts, there was a substantial decrease in heparin-releasable LPL activity at the vascular lumen following 3 h of IL infusion, an effect unrelated to changes in gene and protein expression or whole-body insulin resistance. Although constant perfusion of CON hearts with heparin stripped off most of the luminal bound LPL, hearts from IL-infused animals continued to release excessive amounts of the enzyme, suggesting buildup of LPL within endothelial cells or at the endothelial basolateral surface. Immunogold labeling confirmed this observation and demonstrated robust anti-LPL staining at these sites, only in IL hearts. Perfusing hearts from IL-rats in vitro, in the absence of TG, allowed the accumulated enzyme pool to transfer to the coronary lumen. CONCLUSION: Our data suggest that acute amplification of lipids reduces cardiac luminal LPL but facilitates additional recruitment of cardiomyocyte enzyme. Should this mechanism occur globally, it could contribute towards management of hyperlipidemia.

Animals↗

PubMed2006

Store-operated Ca2+ entry modulates sarcoplasmic reticulum Ca2+ loading in neonatal rabbit cardiac ventricular myocytes.

Store-operated Ca2+ entry (SOCE), which is Ca2+ entry triggered by the depletion of intracellular Ca2+ stores, has been observed in many cell types, but only recently has it been suggested to occur in cardiomyocytes. In the present study, we have demonstrated SOCE-dependent sarcoplasmic reticulum (SR) Ca2+ loading (load(SR)) that was not altered by inhibition of L-type Ca2+ channels, reverse mode Na+/Ca2+ exchange (NCX), or nonselective cation channels. In contrast, lowering the extracellular [Ca2+] to 0 mM or adding either 0.5 mM Zn2+ or the putative store-operated channel (SOC) inhibitor SKF-96365 (100 microM) inhibited load(SR) at rest. Interestingly, inhibition of forward mode NCX with 30 microM KB-R7943 stimulated SOCE significantly and resulted in enhanced load(SR). In addition, manipulation of the extracellular and intracellular Na+ concentrations further demonstrated the modulatory role of NCX in SOCE-mediated SR Ca2+ loading. Although there is little knowledge of SOCE in cardiomyocytes, the present results suggest that this mechanism, together with NCX, may play an important role in SR Ca2+ homeostasis. The data reported herein also imply the presence of microdomains unique to the neonatal cardiomyocyte. These findings may be of particular importance during open heart surgery in neonates, in which uncontrolled SOCE could lead to SR Ca2+ overload and arrhythmogenesis.

Age Factors↗

PubMed2005

Critical role of actin in modulating BBB permeability.

A major obstacle in the treatment of degenerative manifestations and debilitating diseases in the central nervous system (CNS) lies in the impediment of drug delivery into these tissues. The impediment is due to a membrane barrier referred to as the blood-brain barrier (BBB). It is known that the BBB is a unique membranous structure in brain capillaries that tightly segregates the brain from systemic blood circulation. It is imperative to have a thorough understanding of the molecular components and their integrated function of this barrier to develop effective therapeutics for CNS disorders and diseases. Although there are other cell and biochemical properties that underlie this barrier function, it is well established that the barrier is mainly made up of the physical elements of tight junction (TJ) complex. The major constituents of TJ, such as occludin, claudins, zonula occludens (ZOs) and junctional adhesion molecule (JAM) have been subjects of intensive studies and reviews. However, after examining currently proposed models, we have come to believe that a cytoskeletal component-actin may play a critical role in interacting TJ molecular constituents and modulating functional TJ complex. In this review, we will discuss the correlation of temporal and spatial distribution and remodeling of actin filaments with altering integrity of TJ complexes in various systems and present a hypothesis to depict its potential role in modulating BBB permeability.

Actins↗

PubMed2005

Mechanism of ACh-induced asynchronous calcium waves and tonic contraction in porcine tracheal muscle bundle.

Stimulation of the tracheal muscle bundle by acetylcholine (ACh) results in the generation of asynchronous repetitive Ca2+ waves (ACW) in intact tracheal smooth muscle (TSM) cells. We showed previously that ACW underlie cholinergic excitation-contraction coupling in porcine TSM and that Ca2+ entry through the L-type voltage-gated Ca2+ channel (VGCC) contributes partially to maintenance of the ACW. However, the mechanism of the ACW remains undefined. In this study, we pharmacologically characterized the mechanism of ACh-induced ACW in the intact porcine tracheal muscle bundle. We found that inhibition of receptor-operated channels/store-operated channels (ROC/SOC) by SKF-96365 completely abolished the nifedipine-insensitive component of ACh-mediated ACW and tonic contraction. Blockade of Na+/Ca2+ exchange with KB-R7943 or 2',4'-dichlorobenzamil or removal of extracellular Na+ resulted in nearly complete inhibition of the nifedipine-insensitive component of ACh-mediated ACW and tonic contraction. Inhibition of the sarco(endo)plasmic reticulum Ca2+-ATPase by cyclopiazonic acid abolished the ongoing ACW. Application of 2-aminoethoxydiphenyl borate (2-APB) or xestospongin C to inhibit the inositol 1,4,5-trisphosphate-sensitive sarcoplasmic reticulum (SR) Ca2+ release channels produced no effect on ACh-mediated ACW and tonic contraction. However, pretreatment with caffeine or ryanodine inhibited ACh-induced ACW. Furthermore, application of procaine or tetracaine prevented the generation and abolished the ongoing ACh-mediated ACW and tonic contraction. Collectively, these results indicate that the ACh-stimulated ACW in porcine TSM are produced by repetitive cycles of Ca2+ release from SR through 2-APB- and xestospongin C-insensitive Ca2+ release channels, and plasmalemmal Ca2+ entry involving reverse-mode Na+/Ca2+ exchange, ROC/SOC, and L-type VGCC is required to refill the SR via SERCA to support the ongoing ACW.

Acetylcholine↗

PubMed2005

The critical component to establish in vitro BBB model: Pericyte.

The blood-brain barrier (BBB), a highly regulated membranous barrier of brain capillaries, consists of an intricate network of tight junctions (TJs) that segregate the central nervous system (CNS) from systemic blood circulation and maintain a delicate homeostasis of the CNS environment. While endothelial cells (ECs) of brain capillaries are clearly the principal cellular element of BBB, the formation and regulation of intact BBB structure appear to require the interactions of endothelial cells with other cellular components. Astrocytes, one of the major non-neural cells in the brain, associate closely and interact with capillary endothelial cells during the angiogenesis and BBB development. Current in vitro cellular models for the study of BBB functions often incorporate astrocytes with endothelial cells. However, another foremost cell type, CNS pericyte, which intimately embraces brain capillary endothelium, attracts relatively little attention for its role in developing the in vitro BBB system. This review will analyze the critical functions of pericytes in angiogenesis in various systems and discuss the relevance of these functions in mediating the development, maintenance, and regulation of BBB. The author will also discuss the functional role of actin in both ECs and pericytes, and further elaborate the molecular mechanisms of BBB permeability regulation that involves the transduction pathway-mediated actin remodeling process. Finally, the rationale of incorporating pericytes for establishing a better in vitro BBB model will be emphasized.

Actins↗

PubMed2005

15-F(2t)-isoprostane exacerbates myocardial ischemia-reperfusion injury of isolated rat hearts.

Reactive oxygen species induce formation of 15-F(2t)-isoprostane (15-F(2t)-IsoP), a specific marker of in vivo lipid peroxidation, which is increased after myocardial ischemia and during the subsequent reperfusion. 15-F(2t)-IsoP possesses potent bioactivity under pathophysiological conditions. However, it remains unknown whether 15-F(2t)-IsoP, by itself, can influence myocardial ischemia-reperfusion injury (IRI). Adult rat hearts were perfused by the Langendorff technique with Krebs-Henseleit (KH) solution at a constant flow rate of 10 ml/min. 15-F(2t)-IsoP (100 nM), SQ-29548 (1 microM, SQ), a thromboxane receptor antagonist that can abolish the vasoconstrictor effect of 15-F(2t)-IsoP, 15-F(2t)-IsoP + SQ in KH, or KH alone (vehicle control) was applied for 10 min before induction of 40 min of global ischemia followed by 60 min of reperfusion. During ischemia, saline (control), 15-F(2t)-IsoP, 15-F(2t)-IsoP + SQ, or SQ in saline was perfused through the aorta at 60 microl/min. 15-F(2t)-IsoP, 15-F(2t)-IsoP + SQ, or SQ in KH was infused during the first 15 min of reperfusion. Coronary effluent endothelin-1 concentrations were significantly higher in the group treated with 15-F(2t)-IsoP than in the control group during ischemia and also in the later phase of reperfusion (P < 0.05). Infusion of 15-F(2t)-IsoP increased release of cardiac-specific creatine kinase, reduced cardiac contractility during reperfusion, and increased myocardial infarct size relative to the control group. SQ abolished the deleterious effects of 15-F(2t)-IsoP. 15-F(2t)-IsoP exacerbates myocardial IRI and may, therefore, act as a mediator of IRI. 15-F(2t)-IsoP-induced endothelin-1 production during cardiac reperfusion may represent a mechanism underlying the deleterious actions of 15-F(2t)-IsoP.

Animals↗

PubMed2005

Calyculin-A disrupts subplasmalemmal junction and recurring Ca2+ waves in vascular smooth muscle.

Excitation-contraction coupling (E-C coupling) in phenylephrine(PE)-stimulated rabbit inferior vena cava (IVC) depends on the generation of asynchronous recurring Ca2+ waves in the in situ vascular smooth muscle cells (VSMC). Previous studies by our group have implicated a putative non-selective cationic store-operated channel and the reverse-mode Na+-Ca2+ exchange in refilling of the intracellular Ca2+ store via the sarco/endoplasmic reticulum ATPase (SERCA) and the maintenance of the recurring Ca2+ waves. We hypothesize that for the proper functioning of these three Ca2+ translocators in the process of SR refilling, the plasma membrane (PM) and the underlying superficial sarcoplasmic reticulum (SR) form specialized PM-SR junctions, which are essential for the maintenance of the recurring Ca2+ waves. In order to test this hypothesis, calyculin-A, a serine/threonine phosphatase inhibitor that has been demonstrated to result in the disruption of the PM-SR junctions was used. In the control rabbit IVC, electron microscopy of the in situ VSMC indicates that 14.2+/-0.7% of the PM is closely apposed by the prominent superficial SR network, forming numerous flattened PM-SR junctional cytoplasmic spaces. In the control IVC stimulation with 5 microM PE resulted in sustained recurring Ca2+ waves with a frequency of 0.42+/-0.02 Hz. In calyculin-A treated rabbit IVC, a concentration-dependent dissociation of the superficial SR and loss of PM-SR junctions was observed. This progressive loss of the PM-SR junctions occurs over the same concentration range as the inhibition of PE-induced recurring Ca2+ waves. These findings offer support for the hypothesis that the presence of the PM-SR junctions is required for the generation of asynchronous recurring Ca2+ waves, which underlie excitation-contraction coupling in the VSMC of the rabbit IVC.

Action Potentials↗

PubMed2005

Rearrangement of the close contact between the mitochondria and the sarcoplasmic reticulum in airway smooth muscle.

The mitochondria and the sarcoplasmic reticulum (SR) are two major intracellular calcium-storing organelles that exhibit close functional interaction with each other. Close spatial association is believed to be important for their functional interaction. In this study, we have characterized the spatial relationship between the SR and the mitochondria in porcine tracheal smooth muscle cells (TSMC) under different conditions. By examining the cross-section of unstimulated TSMC with electron microscopy, we found that 99.4 +/- 0.5% of the mitochondria seen on random cross-sections were situated within 30 nm of the SR and that 82.2 +/- 6.7% of the mitochondria were completely enveloped by the SR network. Overall, 48.0 +/- 3.5% of the mitochondrial outer membrane was within 30 nm with the SR. After stimulation of the TSMC with acetylcholine (ACh) or 80 mM [K(+)] solution 97.0 +/- 2.1% and 98.6 +/- 1.4% of the mitochondria observed were situated within 30 nm of the SR, respectively. However, the proportion of the mitochondria that was completely enveloped by the SR was significantly reduced to 12.2 +/- 5.9% in ACh-stimulated cells and 9.7 +/- 6.6% in 80 mM [K(+)] stimulated cells. The percentage of mitochondrial membrane closely associated with the SR was correspondingly lower at 10.1 +/- 1.0% during ACh stimulation and 10.8 +/- 0.9% during 80 mM [K(+)] stimulation. During smooth muscle cell stimulation, the SR appears to unwrap from the mitochondria and extend into the cytoplasm while maintaining close contact with the mitochondria over a smaller area. Such static and dynamic components of the close spatial association between the mitochondria and the SR may serve as a structural basis for the selective and efficient Ca(2+) trafficking between the two organelles in TSMC.

Acetylcholine↗

PubMed2005

Endothelin A and B receptor antagonist bosentan reduces postischemic myocardial injury in the rat: critical timing of administration.

The purpose of this study was to investigate the effects of bosentan, a mixed endothelin receptor A and B subtype antagonist, on myocardial ischemia-reperfusion injury and to explore the influence of the timing of bosentan administration on its cardioprotective effects. Adult rat hearts were perfused by the Langendorff technique with Krebs-Henseleit solution (KH) at a constant flow rate at 10 mL/min. Global myocardial ischemia was induced by stopping KH perfusion for 40 min, and this was followed by 60 min of reperfusion. Hearts were randomized to 1 of 3 experimental groups (n = 7 each): untreated control; treatment with bosentan 1 micromol/L 10 min prior to, during 40 min global ischemia, and for 15 min of reperfusion (BOS); or treatment with bosentan 1 micromol/L after 15 min of reperfusion (BOS-R). We observed that BOS-R, but not the BOS treatment regimen, significantly reduced the release of cardiac-specific creatine kinase and postischemic myocardial infarct size (P < 0.05 vs. control) without affecting myocardial contractility. Left ventricular developed pressure in the BOS group was significantly (P < 0.01) lower than that in the control group throughout reperfusion. It is concluded that pharmacologically delayed antagonism of endothelin-1 during reperfusion attenuates postischemic myocardial injury. Endothelin-1 antagonist application during early reperfusion may exacerbate postischemic myocardial dysfunction.

Animals↗

PubMed2004

Inhibition of iNOS augments cardiovascular action of noradrenaline in streptozotocin-induced diabetes.

OBJECTIVE: The aim was to determine if inducible nitric oxide synthase (iNOS) contributes to depressed cardiovascular function at the acute phase of streptozotocin-induced diabetes. METHODS: Male Wistar rats were injected with streptozotocin [60 mg/kg, intravenously (i.v.)] or the vehicle (0.9% NaCl) and were studied 3 weeks later. RESULTS: The diabetic and control rats had similar mean arterial pressure (MAP) and total peripheral resistance (TPR). Noradrenaline (NA) increased in vivo left ventricular contractility (LV +dP/dt), MAP and TPR in both groups; however, the responses were markedly less in the diabetic than control rats. Acute administration of 1400W (selective inhibitor of iNOS; 3 mg/kg followed by 3 mg/kg/h, i.v.) did not alter responses to NA in the control rats, but augmented the influence of NA on MAP, TPR and LV +dP/dt in the diabetic rats. At this time, reverse transcription-polymerase chain reaction (RT-PCR) products (RNA) of iNOS were present in the hearts of the diabetic but not control rats. The activity of iNOS was threefold higher in the hearts of the diabetic rats relative to the controls, and the increase was inhibited by 1400W. Furthermore, immunostaining (proteins) of iNOS and nitrotyrosine (NT; marker of peroxynitrite) were identified in the hearts of the diabetic but not control rats. In contrast, the RT-PCR products of eNOS, activity of eNOS and immunostaining of eNOS were of similar intensity in the hearts of both groups. CONCLUSIONS: Activation of iNOS contributes to depressed cardiovascular contractile function to NA at the acute phase of streptozotocin-induced diabetes. Selective inhibition of iNOS partially restored cardiovascular responses to NA.

Acute Disease↗

PubMed2004

Brief episode of STZ-induced hyperglycemia produces cardiac abnormalities in rats fed a diet rich in n-6 PUFA.

Diabetic patients are particularly susceptible to cardiomyopathy independent of vascular disease, and recent evidence implicates cell death as a contributing factor. Given its protective role against apoptosis, we hypothesized that dietary n-6 polyunsaturated fatty acid (PUFA) may well decrease the incidence of this mode of cardiac cell death after diabetes. Male Wistar rats were first fed a diet rich in n-6 PUFA [20% (wt/wt) sunflower oil] for 4 wk followed by streptozotocin (STZ, 55 mg/kg) to induce diabetes. After a brief period of hyperglycemia (4 days), hearts were excised for functional, morphological, and biochemical analysis. In diabetic rats, n-6 PUFA decreased caspase-3 activity, crucial for myocardial apoptosis. However, cardiac necrosis, an alternative mode of cell death, increased. In these hearts, a rise in linoleic acid and depleted cardiac glutathione could explain this "switch" to necrotic cell death. Additionally, mitochondrial abnormalities, impaired substrate utilization, and enhanced triglyceride accumulation could have also contributed to a decline in cardiac function in these animals. Our study provides evidence that, in contrast to other models of diabetic cardiomyopathy that exhibit cardiac dysfunction only after chronic hyperglycemia, n-6 PUFA feeding coupled with only 4 days of diabetes precipitated metabolic and contractile abnormalities in the heart. Thus, although promoted as being beneficial, excess n-6 PUFA, with its predisposition to induce obesity, insulin resistance, and ultimately diabetes, could accelerate myocardial abnormalities in diabetic patients.

Animal Feed↗

PubMed2004

Contractile filament architecture and force transmission in swine airway smooth muscle.

It is well known that the cyclic interaction of myosin cross bridges with actin filaments is responsible for force and shortening generation in smooth muscle. The intracellular organization of contractile filaments, however, is still poorly understood. Here, we show electron microscopic and functional evidence that contractile filaments in airway smooth muscle lie parallel to the longitudinal axis of the cell bundle, in contrast to the obliquely arranged filaments depicted in conventional models. The parallel arrangement of contractile filaments is maintained despite the fact that individual cells are spindle-shaped. This is accomplished through filament attachment to membrane-associated dense plaques that are in turn connected to similar structures on neighboring cells. Intracellularly, the parallel arrangement is maintained despite the centrally located nucleus. This is accomplished by attachment of actin filaments to the nuclear envelope and making the nucleus a force transmitting structure. The results suggest that smooth muscle cells in tissue form a mechanical syncytium and are able to function properly only as a group.

Actins↗

PubMed2004

Organellar junctions promote targeted Ca2+ signaling in smooth muscle: why two membranes are better than one.

Numerous cellular processes are regulated by fluctuations in the concentration of a single cation, Ca(2+). To accomplish this feat, cells have developed mechanisms that target Ca(2+) signals to specific effectors in both space, by strategically localizing effectors and ion-transporting molecules, and time, by encoding the regulation of the frequency of Ca(2+) oscillations. With an emphasis on smooth muscle, we have analyzed how the interaction of Ca(2+) transporters located on closely apposing membranes of the plasma membrane, sarcoplasmic reticulum and mitochondria provides the structural foundation for site-specific and time-specific Ca(2+) signaling. These junctional membrane complexes can either control the concentration of Ca(2+) in the microdomain that surrounds an effector molecule or deliver Ca(2+) from the translocator on one membrane to a second translocator on the opposing membrane without significant diffusion into the bulk cytosol, an event we term 'linked Ca(2+) transport'.

Calcium↗

PubMed2003

Relationship between asynchronous Ca2+ waves and force development in intact smooth muscle bundles of the porcine trachea.

Fluctuations in intracellular calcium concentration ([Ca2+]i) constitute the main link in excitation-contraction coupling (E-C coupling) in airway smooth muscle cells (ASMC). It has recently been reported that ACh induces asynchronous recurring Ca2+ waves in intact ASMC of murine bronchioles. With the use of a novel technique allowing us to simultaneously measure subcellular [Ca2+]i and force generation in ASMC located within an intact tracheal muscle bundle, we examined a similar pattern of Ca2+ signaling in the trachea. We found that application of ACh resulted in the generation of recurring intracellular Ca2+ waves progressing along the longitudinal axis of the ribbon-shaped intact ASMC. These Ca2+ waves were not synchronized between neighboring cells, and induction of wave-like [Ca2+]i oscillations was temporally associated with development of force by the tracheal muscle bundle. By comparing the concentration dependence of force generation and the parameters characterizing the [Ca2+]i oscillations, we found that the concentration-dependent increase in ACh-induced force development by the tracheal smooth muscle bundle is achieved by differential recruitment of intact ASMC to initiate Ca2+ waves and by enhancement in the frequency of [Ca2+]i oscillations and elevation of interspike [Ca2+]i once the cells are recruited. Our findings demonstrate that asynchronous recurring Ca2+ waves underlie E-C coupling in ACh-induced contraction of the intact tracheal smooth muscle bundle. Furthermore, in contrast to what was reported in enzymatically dissociated ASMC, Ca2+ influx through the L-type voltage-gated Ca2+ channel was not an obligatory requirement for the generation of [Ca2+]i oscillations and development of force in ACh-stimulated intact ASMC.

Acetylcholine↗

PubMed2003

Structure-function correlation in airway smooth muscle adapted to different lengths.

Airway smooth muscle is able to adapt and maintain a nearly constant maximal force generation over a large length range. This implies that a fixed filament lattice such as that found in striated muscle may not exist in this tissue and that plastic remodeling of its contractile and cytoskeletal filaments may be involved in the process of length adaptation that optimizes contractile filament overlap. Here, we show that isometric force produced by airway smooth muscle is independent of muscle length over a twofold length change; cell cross-sectional area was inversely proportional to cell length, implying that the cell volume was conserved at different lengths; shortening velocity and myosin filament density varied similarly to length change: increased by 69.4% +/- 5.7 (SE) and 76.0% +/- 9.8, respectively, for a 100% increase in cell length. Muscle power output, ATPase rate, and myosin filament density also have the same dependence on muscle cell length: increased by 35.4% +/- 6.7, 34.6% +/- 3.4, and 35.6% +/- 10.6, respectively, for a 50% increase in cell length. The data can be explained by a model in which additional contractile units containing myosin filaments are formed and placed in series with existing contractile units when the muscle is adapted at a longer length.

Adaptation, Physiological↗

PubMed2003

Agonist-induced mitochondrial Ca2+ transients in smooth muscle.

We investigated the role of mitochondria (MT) in calcium signaling in a culture of rat aortic smooth muscle cells. We used targeted aequorin to selectively measure [Ca2+] in this organelle. Our results reveal that smooth muscle cell stimulation with agonists causes a large, transient increase in mitochondrial [Ca2+] ([Ca2+]m). This large transient can be blocked with inhibitors of the sarco-endoplasmic reticulum Ca2+-ATPase, suggesting a close relationship between the sarcoplasmic reticulum (SR) and the mitochondria. FCCP completely abolished the response to agonists, and targeted mitochondrial GFP revealed a vast tubular network of MT in these cells. When added before stimulation with ATP, IP3 inhibitors partially blocked the ATP-induced rise in mitochondrial Ca2+ release. The role of the Na+/Ca2+ exchanger (NCX) was examined by removing extracellular Na+. This procedure prevented the decrease in the [Ca2+]m transient normally seen on removal of extracellular Ca2+. We propose a functional linkage of MT and SR dependent on a narrow junctional space between the two organelles in which Ca2+ diffusion is restricted. Approximately half of the mitochondria appear to be associated with the superficial SR, which communicates with the extracellular space via NCX.

Adenosine Triphosphate↗

PubMed2002

Influence of calcium on myosin thick filament formation in intact airway smooth muscle.

Myosin thick filaments have been shown to be structurally labile in intact smooth muscles. Although the mechanism of thick filament assembly/disassembly for purified myosins in solution has been well described, regulation of thick filament formation in intact muscle is still poorly understood. The present study investigates the effect of resting calcium level on thick filament maintenance in intact airway smooth muscle and on thick filament formation during activation. Cross-sectional density of the thick filaments measured electron microscopically showed that the density increased substantially (144%) when the muscle was activated. The abundance of filamentous myosins in relaxed muscle was calcium sensitive; in the absence of calcium (with EGTA), the filament density deceased by 35%. Length oscillation imposed on the muscle under zero-calcium conditions produced no further reduction in the density. Isometric force and filament density recovered fully after reincubation of the muscle in normal physiological saline. The results suggest that in airway smooth muscle, filamentous myosins exist in equilibrium with monomeric myosins; muscle activation favors filament formation, and the resting calcium level is crucial for preservation of the filaments in the relaxed state.

Actin Cytoskeleton↗