Rho kinase mediates serum-induced contraction in fibroblast fibers independent of myosin LC20 phosphorylation

Fibroblasts form fibers when grown in culture medium containing native type 1 collagen. The contractile forces generated can be precisely quantified and used to analyze the signal transduction pathways regulating fibroblast contraction. Calf serum (30%) induces a sustained contraction that is accompanied by a transient increase in intracellular calcium ([Ca(2+)](i)). W-7, a calmodulin inhibitor, KN-62, an inhibitor of calcium/calmodulin-dependent protein kinase, and ML-7, a myosin light-chain kinase inhibitor, had no effects on either the contraction or the [Ca(2+)](i) responses. Neither genistein, a tyrosine kinase inhibitor, nor calphostin C, a protein kinase C inhibitor, had major effects on force or [Ca(2+)](i). In contrast, the Rho kinase inhibitors (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide (Y-27632) and HA1077 depressed the contraction in a dose-dependent manner without affecting the [Ca(2+)](i) response. Stress fiber formation was also suppressed by Y-27632. Surprisingly, calf serum, Y-27632, and calf serum plus Y-27632 did not alter mono- or diphosphorylation of the myosin regulatory light chain (MRLC) compared with control untreated fibers. These results suggest that the sustained contraction of NIH 3T3 fibroblast fibers induced by calf serum is mediated by Rho kinase but is independent of a sustained increase in [Ca(2+)](i), calcium/calmodulin- or protein kinase C-dependent pathways, or increases in MRLC phosphorylation.

The Na,K-ATPase alpha 2 isoform is expressed in neurons, and its absence disrupts neuronal activity in newborn mice

Na,K-ATPase is an ion transporter that impacts neural and glial physiology by direct electrogenic activity and the modulation of ion gradients. Its three isoforms in brain have cell-type and development-specific expression patterns. Interestingly, our studies demonstrate that in late gestation, the alpha2 isoform is widely expressed in neurons, unlike in the adult brain, in which alpha2 has been shown to be expressed primarily in astrocytes. This unexpected distribution of alpha2 isoform expression in neurons is interesting in light of our examination of mice lacking the alpha2 isoform which fail to survive after birth. These animals showed no movement; however, defects in gross brain development, muscle contractility, neuromuscular transmission, and lung development were ruled out. Akinesia suggests a primary neuronal defect and electrophysiological recordings in the pre-Bötzinger complex, the brainstem breathing center, showed reduction of respiratory rhythm activity, with less regular and smaller population bursts. These data demonstrate that the Na,K-ATPase alpha2 isoform could be important in the modulation of neuronal activity in the neonate.

The sarcoplasmic reticulum and smooth muscle function: evidence from transgenic mice

Smooth muscle Ca2+ handling is of major importance to understanding its function. A new approach utilizes molecular biology to develop transgenic mouse models in which the protein constituents of the various Ca2+ regulatory subsystems have been altered. Gene-targeted or gene-ablated (knockout) mice have been reported for the sarcoplasmic reticulum (SR) Ca2+ pump isoforms SERCA2, SERCA2a and SERCA3, the plasma membrane Ca2+ pump isoforms, PMCA1, PMCA2 and PMCA4, and the SR-associated protein, phospholamban (PLB), an inhibitor of SERCA2. A mouse line carrying a transgene for the smooth muscle specific expression of PLB has been reported. Evidence from studies using these mice combined with the classical pharmacological approaches has provided new insight into the relative role of the SR. We review this field with particular emphasis on PLB, since its modulation of SR function and smooth muscle contractility has the largest database. PLB via modulation of SERCA can play a major role in regulation of both phasic and tonic smooth muscle contractility. The use of transgenic mice has yielded surprises ,uch as PLB modulation of endothelial cell Ca2+ homeostasis, and the demonstration that PLB is the major site for A-kinase-mediated relaxation of mouse bladder. The use of these gene-altered models has provided evidence clearly implicating a major role for the SR in modulating smooth muscle Ca2+ and contractility, with the caveat that this modulation is tissue specific.

Decreased blood pressure and vascular smooth muscle tone in mice lacking basolateral Na(+)-K(+)-2Cl(-) cotransporter

The basolateral Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) functions in the maintenance of cellular electrolyte and volume homeostasis. NKCC1-deficient (Nkcc1(-/-)) mice were used to examine its role in cardiac function and in the maintenance of blood pressure and vascular tone. Tail-cuff measurements demonstrated that awake Nkcc1(-/-) mice had significantly lower systolic blood pressure than wild-type (Nkcc1(+/+)) mice (114.5 +/- 2.2 and 131.8 +/- 2.5 mmHg, respectively). Serum aldosterone levels were normal, indicating that extracellular fluid-volume homeostasis was not impaired. Studies using pressure transducers in the femoral artery and left ventricle showed that anesthetized Nkcc1(-/-) mice have decreased mean arterial pressure and left ventricular pressure, whereas myocardial contraction parameters were not significantly different from those of Nkcc1(+/+) mice. When stimulated with phenylephrine, aortic smooth muscle from Nkcc1(+/+) and Nkcc1(-/-) mice exhibited no significant differences in maximum contractility and only moderate dose-response shifts. In phasic portal vein smooth muscle from Nkcc1(-/-) mice, however, a sharp reduction in mechanical force was noted. These results indicate that NKCC1 can be important for the maintenance of normal blood pressure and vascular tone.

Hypoxic vasorelaxation inhibition by organ culture correlates with loss of Kv channels but not Ca(2+) channels

We (Thorne GD, Shimizu S, and Paul RJ. Am J Physiol Cell Physiol 281: C24-C32, 2001) have recently shown that organ culture for 24 h specifically inhibits relaxation to acute hypoxia (95% N(2)-5% CO(2)) in the porcine coronary artery. Here we show similar results in the porcine carotid artery and the rat and mouse aorta. In the coronary artery, part of the inability to relax to hypoxia after organ culture is associated with a concomitant loss in ability to reduce intracellular Ca(2+) concentration ([Ca(2+)](i)) during hypoxia (Thorne GD, Shimizu S, and Paul RJ. Am J Physiol Cell Physiol 281: C24-C32, 2001). To elucidate the mechanisms responsible for the loss of relaxation to hypoxia, we investigated changes in K(+) and Ca(2+) channel activity and gene expression that play key roles in [Ca(2+)](i) regulation in vascular smooth muscle (VSM). Reduced mRNA expression of O(2)-sensitive K(+) channels (Kv1.5 and Kv2.1) was shown by reverse transcriptase-polymerase chain reaction in the rat aorta. In contrast, no change in other expressed voltage-gated K(+) channels (Kv1.2 and Kv1.3) or Ca(2+) channel subtypes was found. Modified K(+) channel expression is supported by functional evidence indicating a reduced response to general K(+) channel activation, by pinacidil, and to specific voltage-dependent K(+) (Kv) channel blockade by 4-aminopyridine. In conclusion, organ culture decreases expression of specific Kv channels. These changes are consistent with altered mechanisms of VSM contractility that may be involved in Ca(2+)-dependent pathways of hypoxia-induced vasodilation.

Circulatory oxygen transport in the water flea Daphnia magna

To determine the contribution of circulatory convection to tissue oxygen supply in animals of Daphnia magna, heart rate ( f(H)), in-vivo Hb oxygen-saturation ( S(Hb)) and NADH fluorescence intensity ( I(NADH)) as a measure of the tissue oxygenation state were simultaneously measured using digital motion analysis, microabsorption spectroscopy and fluorescence microscopy. In addition, the relationship between stroke volume and body size was established. Groups of differently sized animals (small: 1.4-1.6 mm, medium: 2.7-2.9 mm, large: 3.3 mm) with either low (Hb-poor) or high Hb concentration (Hb-rich) in the hemolymph were exposed to a gradual decrease in ambient oxygen partial pressure ( P(O2amb)) between normoxia and anoxia. In all groups, f(H) increased in response to progressive hypoxia. The hypoxic maximum in f(H) was highest in medium-sized Hb-poor animals, whereas perfusion rate increased continuously with increasing body size in Hb-poor and Hb-rich animals. The P(O2amb) at which Hb in the heart region was half-saturated (in-vivo P(50)) was higher in medium-sized (Hb-poor: 3.2 kPa, Hb-rich: 2.0 kPa) than in small (Hb-poor: 2.1 kPa, Hb-rich: 1.5 kPa) and large animals (Hb-poor: 1.9 kPa). The in-vivo P(50) was always lower in Hb-rich than in Hb-poor animals. The I(NADH) indicated an impairment of tissue oxygenation starting at higher critical P(O2amb) with increasing body size and with lower Hb concentration. Model calculations suggest that at the respective critical P(O2amb), circulatory convection delivers less than half of the oxygen demand in Hb-poor animals. In contrast, in Hb-rich animals, the contribution of circulatory convection to tissue oxygen supply at respective critical P(O2amb) was much greater due to the higher concentration of Hb.

Polylysine binding to unphosphorylated smooth muscle myosin enhances formation and stabilizes myosin filaments in vitro

Previously, we demonstrated that positively charged polylysine, our model for biological polyamines, activates the Mg2+ ATPase activity of unphosphorylated smooth muscle myosin and shifts the myosin conformation from the folded 10S to linear 6S form. These effects of polylysine were reversed by the oppositely charged heparin (Szymanski et al. (1993) Am J Physiol 265, C379). In the present report, we provide further information on polylysine binding to smooth muscle myosin, and test the hypothesis that polylysine binding to unphosphorylated myosin involves filament formation. To relate the effects of polylysine on contractility in smooth muscle to physiologically relevant material, we investigated the ability of naturally occurring positively charged polyamines, histones, cadaverine, putrescine and spermidine to activate the Mg2+ ATPase activity of unphosphorylated smooth muscle myosin. Our data show that polylysine binding to individual unphosphorylated myosin molecules stimulates formation of myosin filaments. Polylysine also interacts with myosin filaments, causing enhancement of their size and the numbers, and this could be reversed by heparin. Polylysine binding to myosin filaments made them more resistant to disassembly by high salt concentrations (KCl) or ATP. Naturally occurring polyamines in millimolar concentrations activate the Mg2+ ATPase activity of unphosphorylated smooth muscle myosin. We suggest that the electrostatic interactions between naturally occurring positively charged polyamines and unphosphorylated smooth muscle myosin may play a role in stabilization of thick filament structurein situ.

Aquaporin 5-deficient mouse lungs are hyperresponsive to cholinergic stimulation

Although aquaporin 5 (AQP5) is the major water channel expressed in alveolar type I cells in the lung, its actual role in the lung is a matter of considerable speculation. By using immunohistochemical staining, we show that AQP5 expression in mouse lung is not restricted to type I cells, but is also detected in alveolar type II cells, and in tracheal and bronchial epithelium. Aqp5 knockout (Aqp5(-/-)) mice were used to analyze AQP5 function in pulmonary physiology. Compared with Aqp5(+/+) mice, Aqp5(-/-) mice show a significantly increased concentration-dependent bronchoconstriction to intravenously administered Ach, as shown by an increase in total lung resistance and a decrease in dynamic lung compliance (P < 0.05). Likewise, Penh, a measure of bronchoconstriction, was significantly enhanced in Aqp5(-/-) mice challenged with aerosolized methacholine (P < 0.05). The hyperreactivity to bronchoconstriction observed in the Aqp5(-/-) mice was not due to differences in tracheal smooth muscle contractility in isolated preparations or to altered levels of surfactant protein B. These data suggest a novel pathway by which AQP5 influences bronchoconstriction. This observation is of special interest because studies to identify genetic loci involved in airway hyperresponsiveness associated with asthma bracket genetic intervals on human chromosome 12q and mouse chromosome 15, which contain the Aqp5 gene.

Loss of SM-B myosin affects muscle shortening velocity and maximal force development

We used an exon-specific gene-targeting strategy to generate a mouse model deficient only in the SM-B myosin isoform. Here we show that deletion of exon-5B (specific for SM-B) in the gene for the heavy chain of smooth muscle myosin results in a complete loss of SM-B myosin and switching of splicing to the SM-A isoform, without affecting SM1 and SM2 myosin content. Loss of SM-B myosin does not affect survival or cause any overt smooth muscle pathology. Physiological analysis reveals that absence of SM-B myosin results in a significant decrease in maximal force generation and velocity of shortening in smooth muscle tissues. This is the first in vivo study to demonstrate a functional role for the SM-B myosin isoform. We conclude that the extra seven-residue insert in the surface loop 1 of SM-B myosin is a critical determinant of crossbridge cycling and velocity of shortening.

Benefits of haemoglobin in the cladoceran crustaceanDaphnia magna

To determine the contribution of haemoglobin (Hb) to the hypoxia-tolerance of Daphnia magna, we exposed Hb-poor and Hb-rich individuals (2.4–2.8 mm long) to a stepwise decrease in ambient oxygen partial pressure (PO2amb) over a period of 51 min from normoxia (20.56 kPa) to anoxia (&lt;0.27 kPa) and looked for differences in their physiological performance. The haem-based concentrations of Hb in the haemolymph were 49 μmol l–1 in Hb-poor and 337 μmol l–1 in Hb-rich animals, respectively. The experimental apparatus made simultaneous measurement of appendage beating rate (fa), NADH fluorescence intensity (INADH) of the appendage muscles, heart rate (fh) and in vivo Hb oxygen-saturation possible. In response to progressive, moderate hypoxia, both groups showed pronounced tachycardia and a slight decrease in fa. The fa and fh of Hb-rich animals were generally 4–6 % lower than those of Hb-poor animals. In addition, Hb-rich animals showed a significant decrease in the PO2amb at which the Hb in the heart region was half-saturated and a striking reduction in the critical PO2amb of appendage-related variables. In Hb-poor animals, the INADH signal indicated that the oxygen supply to the limb muscle tissue started to become impeded at a critical PO2amb of 4.75 kPa, although the high level of fa was largely maintained until 1.77 kPa. The obvious discrepancy between these two critical PO2amb values suggested an anaerobic supplementation of energy provision in the range 4.75–1.77 kPa. The fact that INADH of Hb-rich animals did not rise until PO2amb fell below 1.32 kPa strongly suggests that the extra Hb available to Hb-rich animals ensured an adequate oxygen supply to the limb muscle tissue in the PO2amb range 4.75–1.32 kPa. This finding illustrates the physiological benefit of Hb in enabling the animal to sustain its aerobic metabolism as the energetically most efficient mode of fuel utilization under conditions of reduced oxygen availability.

Phospholamban regulation of bladder contractility: evidence from gene-altered mouse models

1. Phospholamban (PLB) is an inhibitor of the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA). Its presence and/or functional significance in contractility of bladder, a smooth muscle tissue particularly dependent on SR function, is unknown. We investigated this by measuring the effects of carbachol (CCh) on force and [Ca2+]i in bladder from mice in which the PLB gene was ablated (PLB-KO mice). In the PLB-KO bladder, the maximum increases in [Ca2+]i and force were significantly decreased (41.5 and 47.4 % of WT), and the EC50 values increased. 2. Inhibition of SERCA with cyclopiazonic acid (CPA) abolished these differences between WT and PLB-KO bladder, localizing the effects to the SR. 3. To determine whether these effects were specific to PLB, we generated mice with smooth-muscle-specific expression of PLB (PLB-SMOE mice), using the SMP8 alpha-actin promoter. Western blot analysis of PLB-SMOE mice showed approximately an eightfold overexpression of PLB while SERCA was downregulated 12-fold. 4. In PLB-SMOE bladders, in contrast, the response of [Ca2+]i and force to CCh was significantly increased and the EC50 values were decreased. CPA had little affect on the CCh-induced increases in [Ca2+]i and force in PLB-SMOE bladder. 5. These results show that alteration of the PLB:SERCA ratio can significantly modulate smooth muscle [Ca2+]i. Importantly, our data show that PLB can play a major role in modulation of bladder contractility.

The alpha(1)- and alpha(2)-isoforms of Na-K-ATPase play different roles in skeletal muscle contractility

The Na-K-ATPase, which maintains the Na(+) and K(+) gradients across the plasma membrane, can play a major role in modulation of skeletal muscle contractility. Although both alpha(1)- and alpha(2)-isoforms of the Na-K-ATPase are expressed in skeletal muscle, the physiological significance of these isoforms in contractility is not known. Evaluation of the contractile parameters of mouse extensor digitorum longus (EDL) was carried out using gene-targeted mice lacking one copy of either the alpha(1)- or alpha(2)-isoform gene of the Na-K-ATPase. The EDL muscles from heterozygous mice contain approximately one-half of the alpha(1)- or alpha(2)-isoform, respectively, which permits differentiation of the functional roles of these isoforms. EDL from the alpha(1)(+/-) mouse shows lower force compared with wild type, whereas that from the alpha(2)(+/-) mouse shows greater force. The different functional roles of these two isoforms are further demonstrated because inhibition of the alpha(2)-isoform with ouabain increases contractility of alpha(1)(+/-) EDL. These results demonstrate that the Na-K-ATPase alpha(1)- and alpha(2)-isoforms may play different roles in skeletal muscle contraction.

EP2 receptors mediate airway relaxation to substance P, ATP, and PGE2

Substance P (SP) and ATP evoke transient, epithelium-dependent relaxation of constricted mouse tracheal smooth muscle. Relaxation to either SP or ATP is blocked by indomethacin, but the specific eicosanoid(s) involved have not been definitively identified. SP and ATP are reported to release PGE2 from airway epithelium in other species, suggesting PGE2 as a likely mediator in epithelium-dependent airway relaxation. Using mice homozygous for a gene-targeted deletion of the EP2 receptor [EP2(-/-)], one of the PGE2 receptors, we tested the hypothesis that PGE2 is the primary mediator of relaxation to SP or ATP. Relaxation in response to SP or ATP was significantly reduced in tracheas from EP2(-/-) mice. There were no differences between EP2(-/-) and wild-type tracheas in their physical dimensions, contraction to ACh, or relaxation to isoproterenol, thus ruling out any general alterations of smooth muscle function. There were also no differences between EP2(-/-) and wild-type tracheas in basal or stimulated PGE2 production. Exogenous PGE2 produced significantly less relaxation in EP2(-/-) tracheas compared with the wild type. Taken together, this experimental evidence supports the following two conclusions: EP2 receptors are of primary importance in airway relaxation to PGE2 and relaxation to SP or ATP is mediated through PGE2 acting on EP2 receptors.

Contractile regulation of the Na(+)-K(+)-2Cl(-) cotransporter in vascular smooth muscle

Vasoconstrictors activate the Na(+)-K(+)-2Cl(-) cotransporter NKCC1 in rat aortic smooth muscle, but the mechanism is unknown. Efflux of (86)Rb(+) from rat aorta in response to phenylephrine (PE) was measured in the absence and presence of bumetanide, a specific inhibitor of NKCC1. Removal of extracellular Ca(2+) completely abolished the activation of NKCC1 by PE. This was not due to inhibition of Ca(2+)-dependent K(+) channels since blocking these channels with Ba(2+) in Ca(2+)-replete solution did not prevent activation of NKCC1 by PE. Stimulation of NKCC1 by PE was inhibited 70% by 75 microM ML-9, 97% by 2 microM wortmannin, and 70% by 2 mM 2,3-butanedione monoxime, each of which inhibited isometric force generation in aortic rings. Bumetanide-insensitive Rb(+) efflux, an indication of Ca(2+)-dependent K(+) channel activity, was reduced by ML-9 but not by the other inhibitors. Stretching of aortic rings on tubing to increase lumen diameter to 120% of normal almost completely blocked the stimulation of NKCC1 by PE without inhibiting the stimulation by hypertonic shrinkage. We conclude that activation of the Na(+)-K(+)-2Cl(-) cotransporter by PE is the direct result of smooth muscle contraction through Ca(2+)-dependent activation of myosin light chain kinase. This indicates that the Na(+)-K(+)-2Cl(-) cotransporter is regulated by the contractile state of vascular smooth muscle.

Is myosin phosphatase regulated in vivo by inhibitor-1? Evidence from inhibitor-1 knockout mice

1. The Ca(2+) sensitivity of smooth muscle contractility is modulated via regulation of phosphatase activity. Protein phosphatase inhibitor-1 (I-1) is the classic type-1 phosphatase inhibitor, but its presence and role in cAMP-dependent protein kinase (PKA) modulation of smooth muscle is unclear. To address the relevance of I-1 in vivo, we investigated smooth muscle function in a mouse model lacking the I-1 protein (I-1((-/-)) mice). 2. Significant amounts of I-1 protein were detected in the wild-type (WT) mouse aorta and could be phosphorylated by PKA, as indicated by (32)P-labelled aortic extracts from WT mice. 3. Despite the significant presence of I-1 in WT aorta, phenylephrine and KCl concentration- isometric force relations in the presence or absence of the PKA pathway activator isoproterenol (isoprenaline) were unchanged compared to I-1((-/-)) aorta. cGMP-dependent protein kinase (PKG) relaxation pathways were also not different. Consistent with these findings, dephosphorylation rates of the 20 kDa myosin light chains (MLC(20)), measured in aortic extracts, were nearly identical between WT and I-1((-/-)) mice. 4. In the portal vein, I-1 protein ablation was associated with a significant (P < 0.05) rightward shift in the EC(50) of isoproterenol relaxation (EC(50) = 10.4 +/- 1.4 nM) compared to the WT value (EC(50) = 3.5 +/- 0.2 nM). Contraction in response to acetylcholine as well as Ca(2+) sensitivity were similar between WT and I-1((-/-)) aorta. 5. Despite the prevalence of I-1 and its activation by PKA in the aorta, I-1 does not appear to play a significant role in contractile or relaxant responses to any pharmacomechanical or electromechanical agonists used. I-1 may play a role as a fine-tuning mechanism involved in regulating portal vein responsiveness to beta-adrenergic agonists.

Hypoxic vasodilation in porcine coronary artery is preferentially inhibited by organ culture

Hypoxia (95% N2-5% CO2) elicits an endothelium-independent relaxation (45-80%) in freshly dissected porcine coronary arteries. Paired artery rings cultured at 37 degrees C in sterile DMEM (pH approximately 7.4) for 24 h contracted normally to KCl or 1 microM U-46619. However, relaxation in response to hypoxia was sharply attenuated compared with control (fresh arteries or those stored at 4 degrees C for 24 h). Hypoxic vasorelaxation in organ cultured vessels was reduced at both high and low stimulation, indicating that both Ca2+-independent and Ca2+-dependent components are altered. In contrast, relaxation to G-kinase (sodium nitroprusside) or A-kinase (forskolin and isoproterenol) activation was not significantly affected by organ culture. Additionally, there was no difference in relaxation after washout of the stimulus, indicating that the inhibition is specific to acute hypoxia-induced relaxation. Simultaneous force and intracellular calcium concentration ([Ca2+]i) measurements indicate the reduction in [Ca2+]i concomitant with hypoxia at low stimulus levels in these tissue is abolished by culture. Our results indicate that organ culture at 37 degrees C specifically attenuates hypoxic relaxation in vascular smooth muscle by altering dynamics of [Ca2+]i handling and decreasing a Ca2+-independent component of relaxation. Thus organ culture can be a novel tool for investigating the mechanisms of hypoxia-induced vasodilation.

Distinct pathways of Ca(2+) sensitization in porcine coronary artery: effects of Rho-related kinase and protein kinase C inhibition on force and intracellular Ca(2+)

Alterations of the Ca(2+) sensitivity of contraction have been reported for porcine coronary artery, but the mechanisms are not clearly understood. We investigated the mechanism(s) of Ca(2+) sensitization in response to the thromboxane A(2) analogue (U46619). Our hypothesis is that different mechanisms of Ca(2+) sensitization could be distinguished by their distinct time courses. Therefore, we measured the time course of [Ca(2+)](i) and isometric force simultaneously in an intact artery after a single addition of U46619. The initial transient phase was associated with Ca(2+) release from the sarcoplasmic reticulum, whereas the maintained phase was associated with Ca(2+) influx. Two distinct types of Ca(2+) sensitization characterized these phases with either protein kinase C (PKC)-mediated or Rho-kinase-mediated mechanisms. Their effects were quite distinct on the basis of the time courses over which the sensitization was effective. PKC inhibition (1 micromol/L calphostin C) had a much greater effect in the initial phase, diminishing the size of the transient and prolonging the rise in force and the decline in [Ca(2+)](i). There were limited effects on the sustained force. Rho-kinase inhibition (10 micromol/L Y27632), in contrast, nearly abolished the sustained force but had a lesser effect on the transient phase. Neither inhibitor had any effect on the force versus [Ca(2+)](i) relations for KCl contractures. Our evidence suggests that both PKC-mediated and Rho-kinase-mediated Ca(2+) sensitizations are present in coronary arteries, but the latter is dominant in thromboxane A(2) receptor-mediated contraction.

Dantrolene reduces serum TNFalpha and corticosterone levels and muscle calcium, calpain gene expression, and protein breakdown in septic rats

The effects of dantrolene on serum TNFalpha and corticosterone levels and on muscle calcium, calpain gene expression, and protein breakdown were studied in rats with abdominal sepsis induced by cecal ligation and puncture. Treatment of rats with 10 mg/kg of dantrolene 2 h before and 8 h after induction of sepsis reduced serum TNFalpha and corticosterone, muscle calcium levels, mRNA levels for m- and mu-calpain, and the muscle specific calpain p94, as well as total and myofibrillar protein breakdown rates, determined as release of tyrosine and 3-methylhistidine, respectively, from incubated extensor digitorum longus muscles. The results support the concept that increased calcium concentrations may be an important mechanism of sepsis-induced muscle protein breakdown. The data also indicate that other mechanisms, in addition to reduced muscle calcium concentrations such as decreased levels of TNFalpha and glucocorticoids, may contribute to the anti-catabolic effects of dantrolene during sepsis. The observations are important from a clinical standpoint because they suggest that the catabolic response in skeletal muscle during sepsis may be prevented by treatment with a calcium antagonist.

Chloride channel function is linked to epithelium-dependent airway relaxation

We previously reported that substance P (SP) and ATP evoke transient, epithelium-dependent relaxation of mouse tracheal smooth muscle. Since both SP and ATP are known to evoke transepithelial Cl- secretion across epithelial monolayers, we tested the hypothesis that epithelium-dependent relaxation of mouse trachea depends on Cl- channel function. In perfused mouse tracheas, the responses to SP and ATP were both inhibited by the Cl- channel inhibitors diphenylamine-2-carboxylate and 5-nitro-2-(3-phenylpropylamino)benzoate. Relaxation to ATP or SP was unaffected by 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS), and relaxation to SP was unaffected by either DIDS or DNDS. Replacing Cl- in the buffer solutions with the impermeable anion gluconate on both sides of the trachea inhibited relaxation to SP or ATP. In contrast, increasing the gradient for Cl- secretion using Cl- free medium only in the tracheal lumen enhanced the relaxation to SP or ATP. We conclude that Cl- channel function is linked to receptor-mediated, epithelium-dependent relaxation. The finding that relaxation to SP was not blocked by DIDS suggested the involvement of a DIDS-insensitive Cl- channel, potentially the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel. To test this hypothesis, we evaluated tracheas from CFTR-deficient mice and found that the peak relaxation to SP or ATP was not significantly different from those responses in wild-type littermates. This suggests that a DIDS-insensitive Cl- channel other than CFTR is active in the SP response. This work introduces a possible role for Cl- pathways in the modulation of airway smooth muscle function and may have implications for fundamental studies of airway function as well as therapeutic approaches to pulmonary disease.

Smooth muscle-targeted overexpression of insulin-like growth factor I results in enhanced vascular contractility

Insulin-like growth factor I (IGF-I) has been postulated to function as a vasodilator. We explored the vasoactive effects of chronic elevations of arterial IGF-I levels in SMP8-IGF-I mice, in which IGF-I is overexpressed in smooth muscle (SM) by means of a SM alpha-actin promoter. Denuded aortas from SMP8-IGF-I mice generated increased force in response to KCl or phenylephrine and had greater sensitivity to KCl depolarization. This is not due to desensitization of a SM NO pathway, as pretreatment with n-omega-nitro-L-arginine affected both wild-type and SMP8-IGF-I aortas to a similar degree. The increased contractility ex vivo is not associated with changes in heart rate or blood pressure. Total smooth muscle myosin heavy chain (SMHC) messenger RNA (mRNA) was greater in SMP8-IGF-I aortas, with preferential expression of SMHC-A. Reciprocal effects on contractility and SMHC mRNA were observed in SMP8-IGFBP-4 animals, in which IGF-binding protein-4 was overexpressed through the same promoter. Also, SM alpha-actin mRNA was increased in the aortas from SMP8-IGF-I mice. In summary, chronic arterial overexpression of IGF-I is associated with increased contractility. These effects differ from those seen after acute exposure to the growth factor and may relate to IGF-mediated changes in expression and relative isoform abundance of critical contractile proteins.

Preferential role of intracellular Ca2+ stores in regulation of isometric force in NIH 3T3 fibroblast fibres

Fibroblast contraction plays a major role in wound repair, but the regulatory mechanisms are not well known. We investigated the relations between isometric force and intracellular calcium concentration ([Ca2+]i) in fibroblast fibres. These fibres were made with mouse NIH 3T3 fibroblasts cultured with native collagen in a three-dimensional matrix. Calf serum (CS; 30%) elicited a monotonic increase in force that attained a maximum within 15 min and could be sustained indefinitely. In contrast, [Ca2+]i increased to a peak at 3 min after CS stimulation, then returned to baseline levels by 10 min. Pretreatment with Ca2+-free medium or the Ca2+-channel antagonist nicardipine (10 microM) blocked the CS-induced [Ca2+]i increase, but force was not affected. KCl (50 mM) stimulation on the other hand, elicited a prolonged increase in [Ca2+]i but did not increase force. Inhibition of the endoplasmic reticulum Ca2+ release with Ca2+-ATPase inhibitors cyclopiazonic acid (5 microM) or thapsigargin (5 microM) nearly abolished (<20% control) the increase in [Ca2+]i and force response to CS. Treatment with ryanodine (10 microM) and caffeine (20 mM) had a similar effect. The phospholipase C inhibitor U73122 (3 microM) reduced the CS-induced increases in [Ca2+]i and force by 70 and 40%, respectively. We conclude that fibroblast isometric force is not coupled to Ca2+ arising from transmembrane influx but is correlated with the transient [Ca2+]i increase due to release from intracellular stores. Store-released Ca2+ may initiate activation pathways for fibroblast force development, but is not required for force maintenance.

Metabolic adaptations to environmental changes in Caenorhabditis elegans

Metabolic adaptations to environmental changes were studied in Caenorhabditis elegans. To assess adjustments in enzyme function, maximum activities of key enzymes of main metabolic pathways were determined. After a 12 h incubation at varying temperatures (10, 20 degrees C) and oxygen supplies (normoxia or anoxia), the activities of the following enzymes were determined at two measuring temperatures in tissue extracts: lactate dehydrogenase (LDH; anaerobic glycolysis), 3-hydroxyacyl-CoA-dehydrogenase (HCDH; fatty acid oxidation), isocitrate dehydrogenases (NAD-IDH, NADP-IDH; tricarboxylic acid cycle) and isocitrate lyase (ICL; glyoxylate cycle). Incubation at 20 degrees C induced a strong increase in maximum LDH activity. Anoxic incubation caused maximum HCDH and NADP-IDH activities and, at 10 degrees C incubation, LDH activity to increase. Maximum NAD-IDH and ICL activities were not influenced by any type of incubation. In order to study the time course of metabolic adaptations to varying oxygen supplies, relative quantities of free and protein-bound NADH were determined in living C. elegans using time-resolved fluorescence spectroscopy. During several hours of anoxia, free and protein-bound NADH showed different time courses. One main result was that just at the moment when the protein-bound NADH had reached a constant level, and the free NADH started to increase rapidly, the worms fell into a rigor state. The data on enzyme activity and NADH fluorescence can be interpreted on the basis of a two-stage model of anaerobiosis.

Effects of microtubule disruption on force, velocity, stiffness and [Ca(2+)](i) in porcine coronary arteries

Force generated by smooth muscle cells is believed to result from the interaction of actin and myosin filaments and is regulated through phosphorylation of the myosin regulatory light chain (LC(20)). The role of other cytoskeleton filaments, such as microtubules and intermediate filaments, in determining the mechanical output of smooth muscle is unclear. In cultured fibroblasts, microtubule disruption results in large increases in force similar to contractions associated with LC(20) phosphorylation (15). One hypothesis, the "tensegrity" or "push-pull" model, attributes this increase in force to the disruption of microtubules functioning as rigid struts to resist force generated by actin-myosin interaction (9). In porcine coronary arteries, the disruption of microtubules by nocodazole (11 microM) also elicited moderate but significant increases in isometric force (10-40% of a KCl contracture), which could be blocked or reversed by taxol (a microtubule stabilizer). We tested whether this nocodazole-induced force was accompanied by changes in coronary artery stiffness or unloaded shortening velocity, parameters likely to be highly sensitive to microtubule resistance elements. Few changes were seen, ruling out push-pull mechanisms for the increase in force by nocodazole. In contrast, the intracellular calcium concentration, measured by fura 2 in the intact artery, was increased by nocodazole in parallel with force, and this was inhibited and/or reversed by taxol. Our results indicate that microtubules do not significantly contribute to vascular smooth muscle mechanical characteristics but, importantly, may play a role in modulation of Ca(2+) signal transduction.

Effects of microtubules and microfilaments on [Ca(2+)](i) and contractility in a reconstituted fibroblast fiber

We used a reconstituted fiber formed when 3T3 fibroblasts are grown in collagen to characterize nonmuscle contractility and Ca(2+) signaling. Calf serum (CS) and thrombin elicited reversible contractures repeatable for >8 h. CS elicited dose-dependent increases in isometric force; 30% produced the largest forces of 106 +/- 12 microN (n = 30), which is estimated to be 0.5 mN/mm(2) cell cross-sectional area. Half times for contraction and relaxation were 4.7 +/- 0.3 and 3.1 +/- 0.3 min at 37 degrees C. With imposition of constant shortening velocities, force declined with time, yielding time-dependent force-velocity relations. Forces at 5 s fit the hyperbolic Hill equation; maximum velocity (V(max)) was 0.035 +/- 0. 002 L(o)/s. Compliance averaged 0.0076 +/- 0.0006 L(o)/F(o). Disruption of microtubules with nocodazole in a CS-contracted fiber had no net effects on force, V(max), or stiffness; force increased in 8, but decreased in 13, fibers. Nocodazole did not affect baseline intracellular Ca(2+) concentration ([Ca(2+)](i)) but reduced ( approximately 30%) the [Ca(2+)](i) response to CS. The force after nocodazole treatment was the primary determinant of stiffness and V(max), suggesting that microtubules were not a major component of fiber internal mechanical resistance. Cytochalasin D had major inhibitory effects on all contractile parameters measured but little effect on [Ca(2+)](i).

H(2)O(2) mediates Ca(2+)- and MLC(20) phosphorylation-independent contraction in intact and permeabilized vascular muscle

One purpose of the current study was to establish whether vasoconstriction occurs in all vessel types in response to H(2)O(2). Isometric force was measured in pulmonary venous and arterial rings, and isobaric contractions were measured in mesenteric arteries and veins in response to H(2)O(2). A second purpose was to determine whether H(2)O(2)-induced contraction is calcium independent. The addition of H(2)O(2) to calcium-depleted (using the Ca(2+) ionophore ionomycin in zero calcium EGTA buffer) muscle caused contraction. Furthermore, permeabilized muscle contracted in response to H(2)O(2) even in zero Ca(2+). The final purpose was to determine whether the 20-kDa regulatory myosin light chain (MLC(20)) phosphorylation plays a role in H(2)O(2)-induced contraction. Pulmonary arterial strips were freeze-clamped at various time points during H(2)O(2)-induced contractions, and the relative amounts of phosphorylated MLC(20) were measured. H(2)O(2) caused dose-dependent contractions that were independent of MLC(20) phosphorylation. ML-9, a myosin light chain kinase inhibitor, had no effect on the H(2)O(2) contractile response. In conclusion, H(2)O(2) induces Ca(2+)- and MLC(20) phosphorylation-independent contraction in pulmonary and systemic arterial and venous smooth muscle.

Effects of hypoxia on isometric force, intracellular Ca(2+), pH, and energetics in porcine coronary artery

When exposed to hypoxic conditions, coronary arteries dilate, which is an important protective response. Although vessel sensitivity to oxygen is well documented, the mechanisms are not known with certainty. To further characterize the mechanisms of oxygen sensing in the coronary artery, we tested the major classes of hypotheses by measuring the effects of hypoxia on energetics, [Ca(2+)](i), K(+) channel function, and pH(i). Hypoxia relaxes porcine coronary arteries stimulated with either KCl or U46619. The extent of relaxation is dependent on both the degree and kind of stimulation. [Ca(2+)](i) was measured in endothelium-denuded arteries using fura 2-AM and ratiometric fluorescent techniques. At lower stimulus levels, hypoxia decreased both force and [Ca(2+)](i). Inhibitor studies suggest that K(Ca) and K(ATP) channels are not involved in the hypoxic relaxation, whereas K(V) channels may play a minor role, if any. Despite the hypoxia-mediated decrease in force, [Ca(2+)](i) was unchanged or increased at high levels of stimulation. Despite a marked increase in lactate content, pH(i) (measured with the ratiometric fluorescent dye BCECF) was also little affected by hypoxia. Measurement of the phosphagen and metabolite profile of freeze-clamped arteries with analytical isotachophoresis indicated that hypoxia increased lactate content by 4-fold and decreased phosphocreatine to 60% of control. However, neither ATP nor P(i) was affected by hypoxia. Interestingly, additional stimulation under hypoxia increased force but not ATP utilization, as estimated from measurements of anaerobic lactate production. Thus, surprisingly, the economy of force maintenance is increased under hypoxia. In porcine coronary artery, both Ca(2+)-dependent and, importantly, Ca(2+)-independent mechanisms are involved in hypoxic vasodilatation. For the latter, mechanisms involving either ATP, [Ca(2+)](i), pH(i), or P(i) cannot be invoked. This novel oxygen sensing mechanism involves a decreased Ca(2+) sensitivity.

A role for smad6 in development and homeostasis of the cardiovascular system

Smad proteins are intracellular mediators of signalling initiated by Tgf-betasuperfamily ligands (Tgf-betas, activins and bone morphogenetic proteins (Bmps)). Smads 1, 2, 3, 5 and 8 are activated upon phosphorylation by specific type I receptors, and associate with the common partner Smad4 to trigger transcriptional responses. The inhibitory Smads (6 and 7) are transcriptionally induced in cultured cells treated with Tgf-beta superfamily ligands, and downregulate signalling in in vitro assays. Gene disruption in mice has begun to reveal specific developmental and physiological functions of the signal-transducing Smads. Here we explore the role of an inhibitory Smad in vivo by targeted mutation of Madh6 (which encodes the Smad6 protein). Targeted insertion of a LacZ reporter demonstrated that Smad6 expression is largely restricted to the heart and blood vessels, and that Madh6 mutants have multiple cardiovascular abnormalities. Hyperplasia of the cardiac valves and outflow tract septation defects indicate a function for Smad6 in the regulation of endocardial cushion transformation. The role of Smad6 in the homeostasis of the adult cardiovascular system is indicated by the development of aortic ossification and elevated blood pressure in viable mutants. These defects highlight the importance of Smad6 in the tissue-specific modulation of Tgf-beta superfamily signalling pathways in vivo.

Respiratory adaptations to running-water microhabitats in mayfly larvae Epeorus sylvicola and Ecdyonurus torrentis, Ephemeroptera

The mayfly larvae Epeorus sylvicola and Ecdyonurus torrentis inhabit either fast-flowing or, for the latter species, calm zones of running water. We studied (1) mechanisms and limitations of oxygen transport in single individuals (oxygen consumption rate, occurrence and rate of gill movements, and heartbeats) in running water of different oxygen concentrations and (2) capacities for anaerobiosis (L-lactate production). Our aim was to look for specific adaptations in the two species to slightly different microhabitats. Epeorus sylvicola, whose immovable gills are not able to generate ventilatory convection, proved to be an oxyconformer at both test temperatures (11 degrees and 15 degrees C). Ecdyonurus torrentis showed a progressively stronger oxyregulatory behavior at higher temperatures. In this species an onset of gill beating was found at moderate hypoxia (below 16 kPa). Ventilating individuals reached maximum rates (300 min-1) of 5-14 kPa. In the case of a further reduction of oxygen partial pressure, the ventilatory rate started to decrease. Ventilatory activity, however, was maintained down to very low oxygen concentrations. Neither in E. sylvicola nor in E. torrentis was experimental evidence found to confirm the hypothesis of a respiratory function of hindgut movements. During hypoxia, the heart rate was constant in both species (E. sylvicola: 80 min-1; E. torrentis: 60 min-1): bradycardia occurred either below 1.5 kPa or below 4 kPa. Anaerobiosis, that is, lactate production, was not detected in either species.

Role of voltage-dependent and Ca(2+)-activated K(+) channels on the regulation of isometric force in porcine coronary artery

We investigated the role of K(+) channels in the regulation of vascular tone in de-endothelialized porcine coronary artery. Isometric force and intracellular Ca(2+) ([Ca(2+)](i)) under resting conditions were increased by treatment with 4-aminopyridine (4-AP, 1 mM), an inhibitor of voltage-dependent K(+) (K(v)) channels, but not by tetraethylammonium chloride (TEA, 1 mM) or charybdotoxin (100 nM), both inhibitors of Ca(2+)-activated K(+) (K(Ca)) channels, or glibenclamide (10 microM), an inhibitor of ATP-sensitive K(+) channels. Under stimulated conditions with 9,11-dideoxy-11alpha, 9alpha-epoxymethano-prostaglandin F(2alpha) (U46619), 4-AP as well as TEA or charybdotoxin increased isometric force and [Ca(2+)](i), but not glibenclamide. 4-AP was the most potent in terms of depolarization of membrane potential compared with TEA or glibenclamide in the presence or absence of EGTA. In the presence of U46619, a high concentration of 4-AP (10 mM) caused a further contraction with oscillations. The force oscillations induced by 4-AP were inhibited by diltiazem (10 microM), an inhibitor of voltage-dependent Ca(2+) channels, or TEA (1 mM), but not by glibenclamide (10 microM). These force oscillations may be associated with the periodic activation of K(Ca) channels. These findings suggested that 4-AP-sensitive K(v) channels play an important role in the control of vascular tone in both resting and stimulated conditions. Moreover, under stimulated conditions, K(Ca) channels also have an important role in the regulation of vascular tone. Dysfunction of these channels induces abnormal vasoconstriction and may be implicated in vascular diseases such as hypertension and vasospasm.

The sites of respiratory gas exchange in the planktonic crustacean daphnia magna: an in vivo study employing blood haemoglobin as an internal oxygen probe

Recent studies on Daphnia magna have revealed that the feeding current is important for uptake of oxygen from the ambient medium. Respiratory gas exchange should therefore mainly occur within the filtering chamber, whose boundaries are formed by the trunk and the extended carapace shell valves. The precise site of gas exchange in the genus Daphnia is, however, a matter of conjecture. We have developed a method of imaging the haemoglobin oxygen-saturation in the circulatory system of transparent animals, which provides an opportunity to localize oxygen uptake from the environment and oxygen release to the tissues. Experiments were carried out at 20 degrees C on 2.8-3.0 mm long parthenogenetic females maintained in hypoxic culturing conditions, which had resulted in an increased haemoglobin content in the haemolymph. In lateral views of D. magna, the highest values of haemoglobin oxygen-saturation occurred near the posterior margin of the carapace and, surprisingly, in the rostral part of the head. The ambient oxygen partial pressures at which haemoglobin was half-oxygenated were 15 mmHg (2.0 kPa) for the posterior carapace region and 6 mmHg (0.8 kPa) for the rostrum. Although not all parts of the circulatory system could be analyzed using this technique, the data obtained from the accessible regions suggest that the inner wall of the carapace is a major site of respiratory gas exchange. Taking the circulatory pattern and the flow pattern of the medium in the filtering chamber into consideration, it becomes clear that the haemolymph, after passing from the limbs to the carapace lacuna, becomes oxygenated while flowing through the ventral part of the double-walled carapace in a posterior direction. The laterally flattened rostral region, where sensory and central nervous system structures are located, seems to have direct diffusive access to ambient oxygen, which could be especially advantageous during severe hypoxia when the convective transport systems fail to supply enough oxygen to that region.

Transgenic overexpression of beta(2)-adrenergic receptors in airway smooth muscle alters myocyte function and ablates bronchial hyperreactivity

beta(2)-Adrenergic receptors (beta(2)AR) act to relax airway smooth muscle and can serve to counteract hyperresponsiveness, although the effect may not be ablative even in the presence of exogenous agonist. Within this signaling cascade that ultimately transduces smooth muscle relaxation, a significant "spare receptor" pool has been hypothesized to be present in the airway. In order to modify the relationship between beta(2)AR and downstream effectors, transgenic mice (TG) were created overexpressing beta(2)AR approximately 75-fold in airway smooth muscle using a mouse smooth muscle alpha-actin promoter. While >90% of these receptors were expressed on the smooth muscle cell surface, the percentage of receptors able to form the agonist-promoted high affinity complex was less than that found with nontransgenic (NTG) cells (R(H) = 18 versus 36%). Nevertheless, beta(2)AR signaling was found to be enhanced. Intact airway smooth muscle cells from TG had basal cAMP levels that were greater than NTG cells. A marked increase in agonist-stimulated cAMP levels was found in the TG ( approximately 200% stimulation over basal) compared with NTG ( approximately 50% over basal) cells. Adenylyl cyclase studies gave similar results and also showed a 10-fold lower EC(50) for TG cells. Tracheal rings from TG mice that were precontracted with acetylcholine had an enhanced responsiveness (relaxation) to beta-agonist, with a 60-fold decrease in the ED(50), indicating that the enhanced signaling imposed by overexpression results in an increase in the coordinated function of the intact airway cells. In vivo studies showed a significantly blunted airway resistance response to the inhaled bronchoconstrictor methacholine in the TG mice. Indeed, with beta-agonist pretreatment, the TG mice displayed no response whatsoever to methacholine. These results are consistent with beta(2)AR being the limiting factor in the transduction system. Increases in the initial component of this transduction system (the beta(2)AR) are sufficient to markedly alter signaling and airway smooth muscle function to the extent that bronchial hyperresponsiveness is ablated, consistent with an anti-asthma phenotype.

Epipodite and fat cells as sites of hemoglobin synthesis in the branchiopod crustacean Daphnia magna

In contrast to the malacostracan crustaceans that use hemocyanin as the oxygen carrier, a number of branchiopod crustaceans, such as the water flea Daphnia magna, utilize hemoglobin (Hb) as the respiratory protein. By means of in situ hybridization (ISH) techniques with subsequent signal amplification using catalyzed reporter deposition, sites of Hb synthesis were localized in Daphnia magna. Based on a previously reported Hb-cDNA sequence, a specific ISH probe was designed and hybridized with the Hb-mRNA in histological sections of adult D. magna. The detection of Hb-mRNA was tissue specific and revealed that Hb is synthesized in fat cells, which play a role in fat and glycogen metabolism, and in epithelial cells of the epipodites, which are involved in osmoregulation. Sites of Hb synthesis have been identified in several invertebrate phyla, including Annelida and Nematoda. However, this is the first example in the class Crustacea, and only the second in the phylum Arthropoda.

Anaerobiosis in the nematode Caenorhabditis elegans

In Caenorhabditis elegans, mortality rates and changes in concentrations of carbohydrate stores and anaerobic end products were determined in anoxic (test) and normoxic (control) animals at two different temperatures (10 and 20 degrees C). The anoxic tolerance of the free-living nematode proved to be well-developed: at 10 degrees C, about 50% of animals had survived a period of 50 h of anoxia. The carbohydrate stores (approximately 30 mmol glycosyl units kg-1 freshweight (FW)) were reduced by two-thirds within 24 h of anoxia at both temperatures. L-lactate, acetate, succinate, and propionate were identified as the main anaerobic end products. The amounts and proportions of the end products were dependent on temperature. They did not accumulate very much in the tissues, but were mainly excreted. During anoxia, the metabolism of C. elegans was depressed to 3-4% of the aerobic value. The food-source Escherichia coli was found to be at least partly alive in the gut of the animals. To separate between anaerobiosis in animals and bacteria, cleaning procedures were applied, and additional control measurements were made: anaerobic end products produced either by E. coli alone or by bacteria-free (axenic) bred nematodes were quantified at identical incubation conditions.

Management of queues in out-patient departments: the use of computer simulation

Notes that patients attending public outpatient departments in Hong Kong spend a long time waiting for a short consultation, that clinics are congested and that both staff and patients are dissatisfied. Points out that experimentation of management changes in a busy clinical environment can be both expensive and difficult. Demonstrates computerized simulation modelling as a potential tool for clarifying processes occurring within such systems, improving clinic operation by suggesting possible answers to problems identified and evaluating the solutions, without interfering with the clinic routine. Adds that solutions can be implemented after they had proved to be successful on the model. Demonstrates some ways in which managers in health care facilities can benefit from the use of computerized simulation modelling. Specifically, shows the effect of changing the duration of consultation and the effect of the application of an appointment system on patients' waiting time.

Hypoxia and alkalinization inhibit endothelium-derived nitric oxide but not endothelium-derived hyperpolarizing factor responses in porcine coronary artery

We investigated the mechanisms by which hypoxia and alkalinization inhibit the endothelium-dependent relaxation to Substance P (SP) in porcine coronary artery. In a KCl contracture, the major component of the SP response is endothelium-derived nitric oxide (EDNO), whereas with receptor-mediated 9,11-dideoxy-llalpha, 9alpha-epoxymethanoprostaglandin F(2alpha) (U46619) stimulation, the SP response is dependent on both EDNO and endothelium-derived hyperpolarization factor. Intracellular alkalinization by NH(4)Cl reduced the peak of SP responses when arteries were contracted with KCl, whereas with U46619 stimulation, the peak was little effected but the duration was shortened. In endothelial cell-denuded arteries, alkalinization with NH(4)Cl shifted the sodium nitroprusside concentration-relaxation relations rightward. The effects of NH(4)Cl in SP- and sodium nitroprusside-induced relaxations were attenuated by decreasing extracellular pH (pH(o)) from 7.4 to 7.2, which normalized intracellular pH (pH(i)) to control levels. In contrast, in U46619 contractures, the SP response in the presence of a NO synthase inhibitor was unaffected by NH(4)Cl. Moreover, hypoxia blunted but did not abolish the responses to SP for U46619 contractures; addition of KCl, however, abolished the SP response under hypoxia. Endothelial [Ca(2+)](i) was measured with fura-2 differentially loaded only into endothelial cells on intact arteries. Despite the attenuation of the SP response in KCl contractures by NH(4)Cl or hypoxia, endothelial [Ca(2+)](i) responses were unchanged. Our results suggest that hypoxia and alkalinization inhibit EDNO but not endothelium-derived hyperpolarization factor relaxations through a mechanism(s) not involving endothelial cell [Ca(2+)](i). Inhibition of EDNO relaxation by alkalinization with NH(4)Cl is likely to occur at the level of activation of guanylate cyclase and/or at a step downstream in smooth muscle.

[Ca2+]i homeostasis and cyclic nucleotide relaxation in aorta of phospholamban-deficient mice

Phospholamban (PLB), a protein localized in the sarcoplasmic reticulum (SR), inhibits the SR Ca2+-ATPase; phosphorylation of PLB relieves this inhibition. We previously reported significant differences in contractility in aorta from mice in which the gene for PLB was ablated (PLB-). In this study, we measured intracellular Ca2+ concentration ([Ca2+]i) with fura 2 in the intact mouse aorta to more directly test the hypothesis that these changes are ascribable to altered SR function in vivo. Ten micromoles per liter of the alpha-agonist phenylephrine (PE) increased [Ca2+]i monotonically to a steady state in the wild-type aorta. In contrast, in PLB- aorta there was an initial rapid increase to a peak [Ca2+]i, which then decreased to a steady state that was lower than that in the wild type. Upon removal of the stimulus (either PE or KCl), the decrease in [Ca2+]i was two times as fast in the PLB- as in the wild-type aorta. There were no significant differences between PLB- and wild-type aortas in the concentration vs. force relations or the time courses of relaxation in response to forskolin or sodium nitroprusside. Interestingly, stimulation of the cAMP pathway before cGMP pathway activation resulted in a significant increase in sensitivity and a difference in relaxation parameters between PLB- and wild-type aortas. Western blot analysis indicated that the PLB-to-sarcoendoplasmic reticulum Ca2+ATPase ratio in the mouse aorta was similar to that in the heart; 20-fold more aortic than heart homogenate was required to achieve a similar level of immunoreactivity. Our data indicate that PLB can play a major role in modulating smooth muscle [Ca(2+)](i) but only a minor role, if any, in cyclic nucleotide-mediated relaxation.

Ablation of the SERCA3 gene alters epithelium-dependent relaxation in mouse tracheal smooth muscle

Sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase 3 (SERCA3), an isoform of the intracellular Ca(2+) pump that has been shown to mediate endothelium-dependent relaxation of vascular smooth muscle, is also expressed in tracheal epithelium. To determine its possible role in regulation of airway mechanical function, we compared tracheal contractility in gene-targeted mice deficient in SERCA3 (SERCA3(-)) with that in wild-type tracheae. Cumulative addition of ACh elicited concentration-dependent increases in isometric force (ED(50) = 2 microM, maximum force = 8 mN/mm(2)) that were identical in SERCA3(-) and wild-type tracheae. After ACh stimulation, substance P (SP) elicited a transient relaxation (42.6 +/- 3.2%, n = 28) in both tracheae. However, the rate of relaxation was significantly (P < 0.04, n = 9) more rapid in the wild-type [half-time (t(1/2)) = 34.3 s] than in the SERCA3(-) (t(1/2) = 61.6 s) trachea. The SP relaxation was reduced by rubbing the trachea, indicative of epithelial cell involvement. This was verified using a perfused trachea preparation. SP in the outside medium had no effect, whereas SP in the perfusate bathing the epithelial side elicited a relaxation. Nitric oxide synthase inhibition (0.2 mM N(omega)-nitro-L-arginine) reduced the SP relaxation by 36.5 +/- 12.5%, whereas the SP effect was abolished by eicosanoid inhibition (10 microM indomethacin). ATP also elicited an epithelium-dependent relaxation similar to SP but with a more rapid relaxation in the SERCA3(-) trachea than in the wild-type trachea. Our results indicate that SERCA3 gene ablation does not directly affect smooth muscle, which is consistent with the distribution of the isoform, but suggest that SERCA3 plays a role in epithelial cell modulation of airway smooth muscle function.

Stimulation of both aerobic glycolysis and Na(+)-K(+)-ATPase activity in skeletal muscle by epinephrine or amylin

Epinephrine and amylin stimulate glycogenolysis, glycolysis, and Na(+)-K(+)-ATPase activity in skeletal muscle. However, it is not known whether these hormones stimulate glycolytic ATP production that is specifically coupled to ATP consumption by the Na(+)-K(+) pump. These studies correlated glycolysis with Na(+)-K(+)-ATPase activity in resting rat extensor digitorum longus and soleus muscles incubated at 30 degrees C in well-oxygenated medium. Lactate production rose three- to fourfold, and the intracellular Na(+)-to-K(+) ratio (Na(+)/K(+)) fell with increasing concentrations of epinephrine or amylin. In muscles exposed to epinephrine at high concentrations (5 x 10(-7) and 5 x 10(-6) M), ouabain significantly inhibited glycolysis by approximately 70% in either muscle and inhibited glycogenolysis by approximately 40 and approximately 75% in extensor digitorum longus and soleus, respectively. In the absence of ouabain, but not in its presence, statistically significant inverse correlations were observed between lactate production and intracellular Na(+)/K(+) for each hormone. Epinephrine had no significant effect on oxygen consumption or ATP content in either muscle. These results suggest for the first time that stimulation of glycolysis and glycogenolysis in resting skeletal muscle by epinephrine or amylin is closely linked to stimulation of active Na(+)-K(+) transport.

Vasoconstrictors and nitrovasodilators reciprocally regulate the Na+-K+-2Cl- cotransporter in rat aorta

Little is known about the function and regulation of the Na+-K+-2Cl- cotransporter NKCC1 in vascular smooth muscle. The activity of NKCC1 was measured as the bumetanide-sensitive efflux of 86Rb+ from intact smooth muscle of the rat aorta. Hypertonic shrinkage (440 mosmol/kgH2O) rapidly doubled cotransporter activity, consistent with its volume-regulatory function. NKCC1 was also acutely activated by the vasoconstrictors ANG II (52%), phenylephrine (50%), endothelin (53%), and 30 mM KCl (54%). Both nitric oxide and nitroprusside inhibited basal NKCC1 activity (39 and 34%, respectively), and nitroprusside completely reversed the stimulation by phenylephrine. The phosphorylation of NKCC1 was increased by hypertonic shrinkage, phenylephrine, and KCl and was reduced by nitroprusside. The inhibition of NKCC1 significantly reduced the contraction of rat aorta induced by phenylephrine (63% at 10 nM, 26% at 30 nM) but not by KCl. We conclude that the Na+-K+-2Cl- cotransporter in vascular smooth muscle is reciprocally regulated by vasoconstrictors and nitrovasodilators and contributes to smooth muscle contraction, indicating that alterations in NKCC1 could influence vascular smooth muscle tone in vivo.

Vasorelaxant properties of parathyroid hormone-related protein in the mouse: evidence for endothelium involvement independent of nitric oxide formation

PTH-related peptide is produced in vascular smooth muscle and is believed to participate in the local control of vascular tone. The recent identification of mid-region PTHrP peptides, as well as the discovery of multiple receptors in blood vessels, raises new questions concerning the mechanisms by which PTHrP relaxes the vasculature. In this study, we examined these mechanisms in two vascular beds of the mouse. PTHrP-(1-34) and PTH-(1-34), but not PTHrP-(38-64) or PTHrP-(38-94), caused concentration-dependent relaxation of pre-contracted aortas and reduced the spontaneous phasic activity of the portal vein. PTHrP and PTH-induced aortic relaxations were largely endothelium dependent, whereas an intact endothelium was not necessary for maximal portal vein relaxation. The endothelium-dependent component of PTHrP and PTH-induced aortic relaxations were unaffected by pretreatment with either L-NNA or indomethacin but were abolished by pretreatment with tetrabutyl ammonium. These results demonstrate that the N-terminal portions of PTHrP and PTH are required for their vasorelaxant activity in the mouse. In addition, maximal relaxant activity of PTHrP and PTH in murine aorta is dependent on the endothelium, which appears to involve the generation of an endothelium-derived hyperpolarizing factor.

Targeted overexpression of parathyroid hormone-related protein (PTHrP) to vascular smooth muscle in transgenic mice lowers blood pressure and alters vascular contractility

PTH-related protein (PTHrP) and its receptor are expressed in vascular smooth muscle cells and are believed to participate in the local regulation of vascular tone. To explore the function of locally produced PTHrP in vascular smooth muscle in vivo, we developed transgenic mice that overexpress PTHrP in smooth muscle using a smooth muscle alpha-actin promoter to direct expression of the transgene. In the PTHrP-overexpressing mice, messenger RNA expression was mainly restricted to smooth muscle-containing tissues. Several founders also expressed the transgene in bone and heart and exhibited striking abnormalities in the development of these tissues. In PTHrP-overexpressing mice, blood pressure was significantly lower than that in wild-type controls (121 +/- 3 vs. 135 +/- 2 mm Hg; P < 0.01). Moreover, the magnitude of the vasorelaxant response to iv infusions of PTHrP-(1-34)NH2 was significantly attenuated in the transgenic animals. A similar desensitization to PTHrP was observed in aortic ring and portal vein preparations. Surprisingly, PTHrP-overexpressing mice were also significantly less responsive to the hypotensive action of infused acetylcholine in vivo and to the relaxant actions of acetylcholine on aortic vessel preparations in vitro. In summary, we have successfully targeted overexpression of PTHrP to the smooth muscle of transgenic mice. When expressed in its normal autocrine/paracrine setting, PTHrP lowers systemic blood pressure and decreases vascular responsiveness to further relaxation by PTHrP and other endothelium-dependent vasorelaxants such as acetylcholine. We postulate that the heterologous desensitization to acetylcholine-induced relaxation in PTHrP-overexpressing blood vessels involves desensitization of second messenger/effector signaling pathways common to PTHrP and acetylcholine.

Reduced blood pressure and increased sensitivity of the vasculature to parathyroid hormone-related protein (PTHrP) in transgenic mice overexpressing the PTH/PTHrP receptor in vascular smooth muscle

PTH-related protein (PTHrP) is produced in vascular smooth muscle, where it is postulated to exert vasorelaxant properties by activation of the PTH/PTHrP type 1 receptor. As a model for studying the actions of locally produced PTHrP in vascular smooth muscle in vivo, we developed transgenic mice that overexpress the PTH/PTHrP receptor (PTHrP-R) in smooth muscle. Oocyte injection with a SMP8-PTHrP-R fusion construct yielded six founder mice. F1 offspring were viable and demonstrated selective overexpression of the SMP8-PTHP-R messenger RNA in smooth muscle-rich tissues. Baseline blood pressure measured in conscious mice by tail sphygmomanometry was significantly lower in the receptor-overexpressing mice than that in controls (117 +/- 4 vs. 133 +/- 3 mm Hg; P < 0.05). In anesthetized animals, iv infusion of PTHrP-(1-34)NH2 caused a significantly greater reduction in blood pressure and total peripheral resistance in transgenic mice than in control animals. Vascular contractility was studied in paired, isometrically mounted aortas from 9-week-old transgenic and wild-type mice. The force of contraction in response to phenlyephrine was not significantly different between transgenic and wild-type mice. However, PTHrP-(1-34) NH2 relaxed aortic vessel preparations from transgenic mice to a greater extent than in controls (77.1 +/- 3% vs. 38.4 +/- 4%; P < 0.001). To determine the impact of overexpression of PTH/PTHrP type 1 receptor and its ligand on the development of the cardiovascular system, double transgenic mice were created by crossing SMP8-PTHrP-R transgenic mice with mice overexpressing PTHrP (SMP8-PTHrP). Double transgenic mice died around day E9 with abnormalities in the developing heart. In conclusion, overexpression of PTH/PTHrP type 1 receptor in vascular smooth muscle of transgenic mice reduces blood pressure, probably through sustained activation of the receptor by endogenous ligand. The cardiovascular defects observed in mice overexpressing both PTHrP and its receptor suggest that PTHrP may play a role in the normal development of the cardiovascular system.

The importance of the feeding current for oxygen uptake in the water flea daphnia magna

In the planktonic crustacean Daphnia magna (Branchiopoda, Cladocera), different views exist on the mechanism of respiratory gas exchange, ranging from gill breathing to general integumentary respiration. The presumed structures for specialized gas exchange are located ventrally within the filter chamber, which is continuously perfused with the ambient medium for food gathering. To localize respiratory gas exchange in D. magna, we determined the contribution of the feeding current to total oxygen transport. Combining microscopy with special optical techniques, we used a phosphorescent oxygen-sensitive dye for oxygen partial pressure (PO2) measurements and applied fluorescent microspheres for flow-rate analysis. Appendage beat rate was determined by digital image-processing. All experiments were carried out on hypoxia-adapted animals with a body length ranging from 2.3 to 2.7 mm at 20 degreesC. External PO2 measurement revealed oxygen depletion in the ventral body region but essentially no change at posterior, lateral and dorsal positions. The PO2 difference between the inflow and outflow of the feeding current was 13.0 mmHg (1.73 kPa). The flow rate of the feeding current ranged from 1.2 to 5.2 ml h-1 and showed a close correlation with appendage beat rate, which varied from 310.4 to 460.7 beats min-1. Model calculations based on the Fick principle suggest that oxygen extraction from the feeding current satisfies most of the total of oxygen requirement of D. magna.

Phospholamban is present in endothelial cells and modulates endothelium-dependent relaxation. Evidence from phospholamban gene-ablated mice

Vascular endothelial cells regulate vascular smooth muscle tone through Ca2+-dependent production and release of vasoactive molecules. Phospholamban (PLB) is a 24- to 27-kDa phosphoprotein that modulates activity of the sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA). Expression of PLB is reportedly limited to cardiac, slow-twitch skeletal and smooth muscle in which PLB is an important regulator of [Ca2+]i and contractility in these muscles. In the present study, we report the existence of PLB in the vascular endothelium, a nonmuscle tissue, and provide functional data on PLB regulation of vascular contractility through its actions in the endothelium. Endothelium-dependent relaxation to acetylcholine was attenuated in aorta of PLB-deficient (PLB-KO) mice compared with wild-type (WT) controls. This effect was not due to actions of nitric oxide on the smooth muscle, because sodium nitroprusside-mediated relaxation in either denuded or endothelium-intact aortas was unaffected by PLB ablation. Relative to denuded vessels, relaxation to forskolin was enhanced in WT endothelium-intact aortas. The endothelium-dependent component of this relaxation was attenuated in PLB-KO aortas. To investigate whether these changes were due to PLB, WT mouse aorta endothelial cells were isolated. Both reverse transcriptase-polymerase chain reaction and Western blot analyses revealed the presence of PLB in endothelial cells, which were shown to be >98% pure by diI-acetylated LDL uptake and nuclear counterstaining. These data indicate that PLB is present and modulates vascular function as a result of its actions in endothelial cells. The presence of PLB in endothelial cells opens new fields for investigation of Ca2+ regulatory pathways in nonmuscle cells and for modulation of endothelial-vascular interactions.

Impaired cardiac performance in heterozygous mice with a null mutation in the sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 (SERCA2) gene

The sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 (SERCA2) gene encodes both SERCA2a, the cardiac sarcoplasmic reticulum Ca2+ pump, and SERCA2b, which is expressed in all tissues. To gain a better understanding of the physiological functions of SERCA2, we used gene targeting to develop a mouse in which the promoter and 5' end of the gene were eliminated. Mating of heterozygous mutant mice yielded wild-type and heterozygous offspring; homozygous mutants were not observed. RNase protection, Western blotting, and biochemical analysis of heart samples showed that SERCA2 mRNA was reduced by approximately 45% in heterozygous mutant hearts and that SERCA2 protein and maximal velocity of Ca2+ uptake into the sarcoplasmic reticulum were reduced by approximately 35%. Measurements of cardiovascular performance via transducers in the left ventricle and right femoral artery of the anesthetized mouse revealed reductions in mean arterial pressure, systolic ventricular pressure, and the absolute values of both positive and negative dP/dt in heterozygous mutants. These results demonstrate that two functional copies of the SERCA2 gene are required to maintain normal levels of SERCA2 mRNA, protein, and Ca2+ sequestering activity, and that the deficit in Ca2+ sequestering activity due to the loss of one copy of the SERCA2 gene impairs cardiac contractility and relaxation.

Levosimendan, a calcium sensitizer in cardiac muscle, induces relaxation in coronary smooth muscle through calcium desensitization

Levosimendan is a pyridazinone-dinitrile derivative belonging to a new class of cardiac inotropic drugs, Ca++ sensitizers. Levosimendan is also a vasodilator both in vitro and in vivo, but its mechanism is not well understood. The cardiac target protein of levosimendan, troponin C, is a Ca++-binding EF-hand protein. This raises the possibility that levosimendan may also interact with smooth muscle EF-hand proteins, such as, calmodulin, the regulatory myosin light chains, or S100 proteins. We investigated the effects of levosimendan on [Ca++]i, and force in porcine coronary arteries, with receptor-mediated (U46619) or KCl stimulation. At high levels of stimulation, levosimendan decreased force without changing or increasing [Ca++]i, measured with the Ca++-sensitive fluorescent probe fura-2 in the intact artery. With lower levels of U46619, levosimendan (1 microM) lowered force by 70% and reduced [Ca++]i by 38%. The relationship between force and [Ca++]i for KCl stimulation are significantly rightward shifted, indicating Ca++ desensitization by levosimendan. In contrast, the phosphodiesterase III inhibitor, milrinone, does not shift the force-Ca++ relations but elicits relaxation via lowering [Ca++]i. There was little change in pHi, indicating that the Ca++ desensitization by levosimendan was not attributable to decreasing pHi. Levosimendan relaxes coronary arteries and lowers [Ca++]i by mechanisms different than milrinone. Our results indicate a lowering of [Ca++]i by levosimendan consistent with opening of potassium channels and a relaxation that is independent of [Ca++]i. Our evidence points to a novel mechanism that might involve the direct effect of levosimendan on the smooth muscle contractile or regulatory proteins themselves.

The role of phospholamban and SERCA3 in regulation of smooth muscle-endothelial cell signalling mechanisms: evidence from gene-ablated mice

It is generally agreed that intracellular Ca2+ stores, the sarco(endo)plasmic-reticulum (SER), affect Ca2+ homeostasis and thus contractility of vascular smooth muscle. There is, however, no general consensus as to the magnitude of the SER contribution to Ca2+ handling, the basis for isoforms of the SER Ca(2+)-ATPases (SERCAs) or the role of an SER-associated regulatory protein, phospholamban (PLB). Although the biochemical and cell biological roles of the SER have been intensely studied in vitro, the development of gene-targeted and transgenic mouse models enables one to extend our information to the in vivo levels. A brief review of the role of PLB and SERCA function in vascular and endothelial cell function is presented. Studies on the PLB gene-ablated mouse indicate that vascular contractility is considerably altered. This is mirrored by changes in intracellular Ca2+. Moreover, differences in contractility of the gene-ablated tissues are eliminated by treatment with cyclopiazonic acid, which pharmacologically abolishes SER function by inhibiting the Ca(2+)-ATPase. Thus PLB modulation of sarcoplasmic reticulum (SR) Ca2+ uptake plays a major role in modulating vascular contractility. It is interesting that endothelium-dependent relaxation was decreased in the PLB-deficient aorta. This is surprising in light of the PLB distribution, thought to be limited to cardiac, slow skeletal and smooth muscle. Our data indicate the presence of PLB in endothelial cells and point to an unrecognized pathway for modulation of endothelial cell [Ca2+]i and vascular contractility. Data from smooth muscle tissues of the SERCA3 gene-ablated mouse demonstrate that this isoform affects endothelium-dependent function, but not that of smooth muscle, consistent with its known distribution. This isoform appears to perform a modulatory function, rather than the more essential role of SERCA2. Gene-targeted and transgenic models provide an important avenue for understanding the role of SER in vascular signalling.