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R Marthan

Publications and source records attributed to R Marthan.

At least 55 records · Page 3Linked to original sources
PubMed1998

Calcium signaling in airway smooth muscle cells is altered by in vitro exposure to the aldehyde acrolein.

We have previously observed that acrolein administered ex vivo to isolated airways alters the subsequent airway responsiveness. To examine the cellular mechanisms involved in this alteration, we have studied the effect of acrolein exposure on calcium signaling in myocytes freshly isolated from rat trachea. We have also studied the effect of acrolein exposure on isometric contraction of rat epithelium-free tracheal rings. Tissues were exposed to a variety of acrolein concentrations from 0.1 to 1 microM and durations from 5 to 15 min. In isolated cells, exposure to acrolein did not modify the resting cytosolic Ca2+ concentration ([Ca2+]i) whatever the concentration or duration of exposure, but altered the pattern of the Ca2+ response to acetylcholine (ACh). ACh typically induces an initial [Ca2+]i rise followed by peaks of decreasing amplitude (oscillations). Exposure to a fixed concentration of acrolein (0.2 microM) for 5 and 10 min significantly enhanced the amplitude of the initial [Ca2+]i rise in response to a low concentration of ACh (0.1 microM) by 50.8 and 77%, respectively. Similarly, exposure for a fixed duration of 10 min significantly enhanced the amplitude of the initial [Ca2+]i rise by 49.4% at an acrolein concentration of 0.3 microM. When cells were stimulated with a high ACh concentration (10 microM), the value of the first [Ca2+]i peak was not changed by acrolein exposure; but the frequency at which subsequent peaks occurred was significantly increased by 44.4% after 10 min of exposure to a fixed concentration of 0.2 microM and by 36.3% following an exposure for a fixed duration of 10 min at the concentration of 0.3 microM. In contrast, acrolein, whatever the concentration, had no effect on the caffeine-induced [Ca2+]i response. In rat epithelium-free tracheal rings, acrolein increased the response to muscarinic stimulation, with a maximal effect observed for an exposure to 0.3 microM for 10 min. The effect of acrolein on the [Ca2+]i response of isolated myocytes occurred over a range of doses similar to that on the contractile response of rings, suggesting that the effect of this pollutant on calcium signaling may account, at least partially, for acrolein-induced airway hyperresponsiveness.

Acetylcholine↗
PubMed1998

[Leukotrienes and airway smooth muscle].

The understanding of cellular and molecular mechanisms involved in the contraction of airway smooth muscle has tremendously advanced in the recent years. Among extracellular messengers that control airway smooth muscle contraction attention has focused on leukotrienes since several strategies for pharmacological interventions in either the production or the effect of these substances have been developed. Two types of receptor, CysLT and BLT, coupled to G proteins, have been identified and airway smooth muscle contraction mostly depends on CysLT1 receptor activation. This activation induces intracellular calcium release leading to an increase in cytoplasmic calcium concentration responsible for airway smooth muscle contraction. Leukotriene antagonists are now available and their role in asthma treatment is being defined.

Anti-Asthmatic Agents↗
PubMed1998

Study of central and peripheral conductions to the diaphragm in 22 patients with definite multiple sclerosis.

Involvement of the diaphragm was evaluated electrophysiologically in 22 patients with definite multiple sclerosis. Magnetic transcranial stimulation (MTS), magnetic cervical stimulation at C4 level (MCS) and electric stimulation of the phrenic nerve at the neck (EPS) were performed for measuring latencies, motor conduction times and amplitudes of the responses recorded with a pair of surface or subcutaneous electrodes located at the xiphoid and the 8th costal interspace on the anterior axillary line. Latency of the motor evoked potentials (MEPs) was abnormal: in 9 patients following MTS, in 6 following MCS, in 2 following EPS. The motor conduction time between the cortex and the cervical spine, we called CMCT1, was abnormal in 11 patients and the motor conduction time between the cortex and the neck, we called CMCT2, was abnormal in 8 patients. However CMCT1 was more often unmeasurable than CMCT2 because the MEPs following MCS were unreliable in 4 patients. The conduction time between the cervical spine and the neck was abnormally long in 2 patients but it was paradoxically abnormally short in 3, probably because of the difficulties in locating exactly the place of the stimulation at the cervical C4 level. The MEP amplitude was not considered a reliable parameter because of the large range of the values in our controls, although the mean amplitude was significantly lower in the patients than in the controls. The amplitude of the compound muscle action potential (CMAP) following EPS was below the lower limit of the normal in 9 patients. The percentage of abnormal MEP latencies and CMCTs when both sides were combined was higher for the hemidiaphragms than for the upper limbs and was roughly the same for the hemidiaphragms and the lower limbs. Moreover electrophysiological study of the diaphragm was abnormal in 5 patients without pulmonary symptoms and with normal pulmonary function tests, demonstrating that this study is useful for revealing infraclinical demyelinating lesions on the central motor pathways down to diaphragm. In addition, alterations of the CMAPs in some patients suggest a possible extension of the lesions towards the anterior horns and anterior roots.

Adult↗
PubMed1997

Oscillatory Cl- current induced by angiotensin II in rat pulmonary arterial myocytes: Ca2+ dependence and physiological implication.

We have previously reported that angiotensin II (ANG II) induces oscillations in the cytoplasmic calcium concentration ([Ca2+]i) of pulmonary vascular myocytes. The present work was undertaken to investigate the effect of ANG II in comparison with ATP and caffeine on membrane currents and to explore the relation between these membrane currents and [Ca2+]i. In cells clamped at -60 mV, ANG II (10 microM) or ATP (100 microM) induced an oscillatory inward current. Caffeine (5 mM) induced only one transient inward current. In control conditions, the reversal potential (Erev) of these currents was close to the equilibrium potential for Cl- ions (Ecl = -2.1 mV) and was shifted towards more positive values in low-Cl- solutions. Niflumic acid (10-50 microM) and DIDS (0.25-1 mM) inhibited this inward current. Combined recordings of membrane current and [Ca2+]i by indo-1 microspectrofluorimetry revealed that ANG II- and ATP-induced currents occurred simultaneously with oscillations in [Ca2+]i whereas the caffeine-induced current was accompanied by only one transient increase in [Ca2+]i. Niflumic acid (25 microM) had no effect on agonist-induced [Ca2+]i responses, whereas thapsigargin (1 microM) abolished both membrane current and the [Ca2+]i response. Heparin (5 mg/ml in the pipette solution) inhibited both [Ca2+]i responses and membrane currents induced by ANG II and ATP, but not by caffeine. In pulmonary arterial strips, ANG II-induced contraction was inhibited by niflumic acid (25 microM) or nifedipine (1 microM) to the same extent and the two substances did not have an additive effect. This study demonstrates that, in pulmonary vascular smooth muscle, ANG II, as well as ATP, activate an oscillatory calcium dependent chloride current which is triggered by cyclic increases in [Ca2+]i and that both oscillatory phenomena are primarily IP3-mediated. It is suggested that ANG II-induced oscillatory chloride current could depolarise the cell membrane leading to activation of voltage-operated Ca2+ channels. The resulting Ca2+ influx contributes to the component of ANG II-induced contraction that is equally sensitive to chloride or calcium channel blockade.

Adenosine Triphosphate↗
PubMed1997

[Ca2+]i oscillations induced by muscarinic stimulation in airway smooth muscle cells: receptor subtypes and correlation with the mechanical activity.

1. Cytosolic calcium concentration ([Ca2+]i) by indo 1 microspectrofluorimetry in freshly isolated cells and isometric contraction of isolated rings were measured in response to muscarinic cholinoceptor stimulation in rat tracheal smooth muscle. 2. In isolated myocytes, acetylcholine (ACh, 0.03-1 microM) caused a rapid and graded increase in [Ca2+]i up to a net amplitude of 492 +/- 26 nM (n = 19) which gradually declined. The EC50 for ACh was 0.13 microM. This first [Ca2+]i peak was followed, when the ACh concentration increased, in approximately 50-60% of the cells, by successive peaks of decreased amplitude ([Ca2+]i oscillations) superimposed on the plateau phase. Whereas the percentage of cells exhibiting [Ca2+]i oscillations remained consistent, the frequency of these oscillations increased to up to 10 min-1 with an ACh concentration of 100 microM. 3. Removal of extracellular calcium (in the presence of EGTA, 0.4 mM) or addition of the voltage-dependent Ca(2+)-channel blocker verapamil (10 microM) did not alter the first [Ca2+]i peak, the plateau or the oscillations induced by ACh or carbachol. In contrast, the specific inhibitor of the sarcoplasmic Ca(2+)-ATPase, thapsigargin (1 microM), completely abolished the [Ca2+]i response. Thapsigargin (1 microM) also blocked the caffeine (5 mM)-induced transient rise in [Ca2+]i. 4. Atropine (a non-selective muscarinic cholinoceptor antagonist) and 4-diphenyl acetoxy N-methyl piperidine (4-DAMP, a selective M3 antagonist) inhibited the [Ca2+]i response to muscarinic cholinoceptor activation with an IC50 of 13 and 20 nM, respectively. Pirenzepine (a selective M1 antagonist) also totally inhibited the [Ca2+]i response to ACh but with a higher IC50 of 2 microM. Methoctramine (a selective M2 antagonist) up to a concentration of 10 microM caused only a 40% inhibition. The effect of muscarinic antagonists on cumulative concentration-response curves (CCRC) for carbachol was assessed at the following concentrations: atropine and 4-DAMP at 3, 10 and 30 nM; pirenzepine 0.3, 1 and 3 microM, and methoctramine at 1, 3 and 10 microM. For these concentrations, all of the antagonists produced a rightward shift of the CCRC for carbachol and pA2 values were 9.2, 8.8, 6.7 and 6.3, respectively. 5. In conclusion, the present study indicates that muscarinic stimulation of rat isolated tracheal smooth muscle cells induces [Ca2+]i oscillations. The occurrence of these oscillations depends on the graded amplitude of the first [Ca2+]i rise and their frequency may play a role in the amplitude of the mechanical activity in response to muscarinic cholinoceptor activation. Both the [Ca2+]i and the contractile responses are primarily dependent on activation of the M3 receptor subtype.

Acetylcholine↗
PubMed1997

Modulation of the calcium sensitivity of the smooth muscle contractile apparatus: molecular mechanisms, pharmacological and pathophysiological implications.

Smooth muscle contraction is the basis of the physiological reactivity of several systems (vascular, respiratory, gastrointestinal, urogenital ...). Hyperresponsiveness of smooth muscle may also contribute to a variety of problems such as arterial hypertension, asthma and spontaneous abortion. An increase in cytoplasmic calcium concentration ([Ca2+]i) is the key event in excitation-contraction coupling in smooth muscle and the relationship linking the [Ca2+]i value to the force of contraction represents the calcium sensitivity of the contractile apparatus (CaSCA). Recently, it has become evident that CaSCA can be modified upon the action of agonists or drugs as well as in some pathophysiological situations. Such modifications induce, at a fixed [Ca2+]i value, either an increase (referred to as sensitization) or a decrease (desensitization) of the contraction force. The molecular mechanisms underlying this modulation are not yet fully elucidated. Nevertheless, recent studies have identified sites of regulation of the actomyosin interaction in smooth muscle. Sensitization primarily results from the inhibition of myosin light chain phosphatase (MLCP) by intracellular messengers such as arachidonic acid or protein kinase C. In addition, phosphorylation of thin filament-associated proteins, caldesmon and calponin, increases CaSCA. Activation of small (monomeric) G-proteins such as rho or ras is also involved. Desensitization occurs as a consequence of phosphorylation of myosin light chain kinase (MLCK) by the calcium-calmodulin activated protein kinase II, or stimulation of MLCP by cyclic GMP-activated protein kinase. In the present review, examples of physiological modulation of CaCSA as well as pharmacological and pathophysiological implications are illustrated for some smooth muscles.

Anesthetics↗
PubMed1996

Effect of modulators of tyrosine kinase activity on agonist-induced contraction in the rat pulmonary vascular smooth muscle.

In the rat isolated main pulmonary artery, we investigated the effect of a tyrosine kinase inhibitor (genistein) and that of a tyrosine phosphatase inhibitor (phenylarsine oxide) on agonist-induced contraction. Genistein (10 microM) reduced the amplitude of the contraction evoked by noradrenaline (0.1-10 microM) or angiotensin II (1-100 nM). Phenylarsine oxide (0.5 microM) increased the amplitude of the contraction evoked by these agonists. The effects of genistein and phenylarsine oxide on agonist-induced contractions were also observed in the presence of verapamil (10 microM). Thapsigargin (0.5 microM) increased the amplitude of the contraction induced by noradrenaline (1-10 microM) or angiotensin II (10-100 nM). Subsequent addition of genistein counteracted the effect of thapsigargin on noradrenaline- and angiotensin II-induced contraction. Dantrolene alone (100 microM) reduced noradrenaline- and angiotensin II- but not KCI-induced contraction. In the presence of dantrolene, genistein and phenylarsine oxide failed to modify noradrenaline- and angiotensin II-induced contraction. Finally, in beta-escin skinned preparations, genistein (10-20 microM) and phenylarsine oxide (0.5-1 microM) did not alter Ca(2+)-induced contraction. These results suggest that a tyrosine kinase activity is involved in the vasoconstrictor action of noradrenaline and angiotensin II in the pulmonary circulation. The stimulation of the tyrosine kinase activity appears to be linked to the depletion of an intracellular Ca2+ store.

Adrenergic alpha-Agonists↗
PubMed1996

Human bronchial smooth muscle responsiveness after in vitro exposure to oxidizing pollutants.

The aims of this work were (1) to determine the dose-response relationship between ex vivo exposure to oxidizing pollutants such as nitrogen dioxide (NO2), the aldehyde acrolein, and ozone (O3), and the reactivity to agonists in isolated human bronchial smooth muscle; and (2) to investigate the alterations in the cellular mechanisms of human airway smooth muscle contraction induced by such exposures. Experiments were performed in isolated human bronchi obtained at thoracotomy. Isometric contraction in response to a variety of agonists was compared between pollutant-exposed preparations and paired controls. Short exposures to NO2, acrolein, or O3 altered the subsequent airway smooth muscle responsiveness in a dose-dependent manner. The cellular mechanisms producing the airway hyperresponsiveness observed in vitro are shared by the three pollutants and include alterations in airway smooth muscle excitation-contraction coupling as well as indirect effects on neutral endopeptidase activity.

Acrolein↗
PubMed1996

Angiotensin II-induced Ca(2+)-oscillations in vascular myocytes from the rat pulmonary artery.

The effect of angiotensin II (ANG II) on the cytosolic calcium concentration ([Ca2+]i) was studied in freshly (2-8 h) isolated myocytes from the main pulmonary artery of the rat. Myocytes were loaded with the fluorescent indicator indo 1 (1 microM for 30 min) and experiments were performed at room temperature. Short (30 s) applications of ANG II (0.01-10 microM) induced cyclic variations oscillations in [Ca2+]i. The ANG II-induced response was typically composed of three to six oscillations of constant duration (9.8 +/- 0.5 s, n = 40) but of decreasing amplitude. The first oscillation increased [Ca2+]i from 119 +/- 4 to 884 +/- 33 nM (n = 32). ANG II-induced response was concentration dependently inhibited by previous addition to the bathing solution of losartan or SR-47436 (0.01-0.1 microM, each), two specific AT1 receptor-antagonists. In Ca(2+)-free external solutions (containing 0.4-1 mM EGTA), ANG II still produced oscillation in [Ca2+]i. These oscillations disappeared in myocytes pretreated with neomycin (0.1 microM), thapsigargin (1 microM), or phorbol 12,13-dibutyrate (PDBu, 1 microM). In contrast to ANG II, caffeine (o.5-10 mM) induced only one transient rise in [Ca2+]i, which was unaltered by neomycin or PDBu but blocked by thapsigargin. These results show that ANG II produces oscillations in [Ca2+]i in pulmonary arterial myocytes via stimulation of AT1 receptors coupled to phospholipase C activation. ANG II-induced oscillations appear to be related to the cycling of Ca2+ ions from an intracellular store (presumably the sarcoplasmic reticulum) by a primarily inositol trisphosphate-dependent Ca2+ release.

Angiotensin II↗
PubMed1996

Effect of extracellular ATP on cytosolic Ca2+ concentration in rat pulmonary artery myocytes.

Changes in cytosolic free Ca2+ concentration ([Ca2+]i) induced by ATP and other P2 purinoceptor agonists were investigated using indo 1 microspectrofluorimetry in single smooth muscle cells of the rat pulmonary artery. ATP (100 microM, 30 s) induced 3-4 cyclic rises in [Ca2+]i of decreasing amplitude. The first peak reached 743 +/- 24 nM from the resting value of 103 +/- 5 nM (n = 86). In approximately 50% of the cells, the ATP-induced [Ca2+]i oscillations were accompanied by a small but maintained rise in [Ca2+]i. In a series of 10 cells, the amplitude of this rise averaged 41 +/- 9 nM. The small rise 1) was also induced by 2-methylthio-ATP (2-MeS-ATP) and alpha,beta-methylene-ATP (alpha,beta-MeATP), 2) was insensitive to thapsigargin (TG, 1 microM), and 3) was abolished by the removal of external Ca2+. ATP-induced [Ca2+]i oscillations 1) were not abolished in the absence of external Ca2+, 2) were suppressed by treatment of the cells with TG (1 microM), and 3) were mimicked by UTP but not by 2-MeS-ATP or alpha,beta-MeATP. Both the number of cells that responded by [Ca2+]i oscillations and the maximal amplitude of the response depended on the agonist (ATP or UTP) concentration. The ATP-induced [Ca2+]i oscillations were not modified by tetracaine (500 microM) but were inhibited by forskolin (1 microM) and by phorbol 12,13-dibutyrate (PDB, 0.03 microM). The effect of PDB was reversed by the protein kinase C antagonist calphostin C (0.01 microM). These results suggest that the ATP-induced [Ca2+]i rise is mediated by the activation of P2x and P2u purinoceptors. Ca2+ entry through the P2x receptor channels produces a small and maintained [Ca2+]i rise. [Ca2+]i rise. Stimulation of P2u purinoceptor induces [Ca2+]i oscillations due to cyclic Ca2+ release from intracellular stores through inositol trisphosphate receptor channels.

Adenosine Triphosphate↗
PubMed1996

Human and rat airway smooth muscle responsiveness after ozone exposure in vitro.

We previously reported that NO2 and acrolein administered ex vivo to the lung altered the subsequent responsiveness of airway smooth muscle. The aim of this study was to determine the dose-response relationship for O3 in both human isolated bronchi and rat tracheae and to investigate the mechanisms underlying O3-induced airway responsiveness. Exposure to 1 ppm O3 for 15 min significantly increased the maximal response to carbachol of rat tracheal rings to 149.6 +/- 5.4% of the reference response to acetylcholine (ACh) compared with that of unexposed rings (131.3 +/- 2.4%, n = 6, P < 0.05). The change in maximal airway responsiveness to carbachol, when plotted against the product of exposure concentration and exposure time to O3, a surrogate for the dose, formed a bell-shaped curve. The peak of this dose-response curve was shifted to the right for human bronchi (50 ppm x min, n = 5) compared with that of rat tracheae (15 ppm x min, n = 6). In the rat trachea, responses to KCl were not altered by O3, whereas those to 5-hydroxytryptamine hydrochloride (5-HT) were significantly increased. Finally, in the absence of external Ca2+, O3 exposure still potentiated the maximal response to carbachol from 73.6 +/- 13.9 to 137.0 +/- 6.0% and that to 5-HT from 21.5 +/- 5.5 to 38.7 +/- 2.2% of the reference ACh response. These results indicate that O3 alters the subsequent in vitro airway responsiveness depending on 1) the dose, 2) the nature of the agonist, and 3) the species investigated. Because in vitro exposure to O3 increases responses to agonists that release intracellular Ca2+ and since this effect is maintained in Ca(2+)-free solution, the mechanism of O3-induced increase in airway smooth muscle responsiveness is likely to involve an enhancement in intracellular Ca2+ release.

Airway Resistance↗
PubMed1996

Pulmonary gas exchange in elderly subjects.

Although important alterations in structure and function develop with age, the hypothesis that the lungs are capable of maintaining adequate gas exchange for the maximum human life span is generally accepted. This hypothesis was examined by measuring arterial oxygen and carbon dioxide tension (Pa,O2 and Pa,CO2) alveolo-arterial differences in oxygen and carbon dioxide tension (PA-a,O2 and Pa-A,CO2), steady state transfer capacity of the lung for carbon monoxide (TL,CO,ss) as well as the gas exchange ratio (R) in a series of 74 healthy subjects aged more than 68 yrs (69-104 yrs). In addition, Pa,O2 and Pa,CO2 were measured in a series of 55 young healthy subjects, who acted as controls. In the elderly subjects, except for TL,CO,ss, there was no significant correlation between any of the other variables and age. However, for a given Pa,CO2, Pa,O2 was always lower in the group of elderly subjects than in the group of young control subjects. TL,CO,ss, as well as TL,CO,ss/minute ventilation (V'k) ratio, was correlated with age, according to the following regression equations: TL,CO,ss (mL.min-1.kPa-1) = 126-0.90 x age (yrs), and TL,CO,ss/V'k (kPa-1 x 10(3)) = 13.5-0.085 x age, respectively. These results show that arterial oxygen tension did not decrease with age in this series of elderly subjects. However, the decrease in steady-state transfer capacity of the lungs for carbon monoxide with age indicates that oxygen transport could be diffusion-limited in elderly subjects, at least when oxygen consumption is increased.

Adult↗
PubMed1995

Control of pulmonary vascular smooth muscle tone by sarcoplasmic reticulum Ca2+ pump blockers: thapsigargin and cyclopiazonic acid.

The effect of thapsigargin (TG) and cyclopiazonic acid (CPA) on the mechanical activity of the rat pulmonary artery were investigated. In chemically (beta-escin)-skinned arterial strips, application of TG (0.1-1 microM) or CPA (0.5-10 microM) prior and throughout the loading procedure of the internal Ca2+ stores (0.3 microM free Ca2+ ions for 8-10 min) concentration dependently inhibited the subsequent contractile response induced by noradrenaline (NA, 10 microM) or caffeine (25 mM). In intact strips repeatedly incubated in a Ca(2+)-containing solution (2.5 mM for 10 min), followed by incubation in a Ca(2+)-free solution 12 min before NA-stimulation, TG and CPA not only inhibited the NA-induced contraction but also increased the tension which appeared during the exposure time to Ca2+. The two phenomena developed with similar time courses. The increase in tension during the readmission of Ca2+ ions was not antagonized by verapamil (10 microM) or nifedipine (1 microM) but was blocked by La3+ (50 microM) and Co2+ (1 mM) ions. The amplitude of the verapamil-insensitive TG (or CPA)-induced contraction was dependent on the external [Ca2+] [0.1-10 mM, concentration for half maximal effect (EC50) = 0.85 mM], not modified by the reduction of the external [Na+] (from 130 to 10 mM) and decreased by depolarization of the strip using K(+)-rich (30-120 mM) solutions. Under the latter condition, 38 +/- 9 and 83 +/- 4% reduction (n = 5) was observed in the presence of 60 and 120 mM K+ respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Cellular mechanisms of hypoxia-induced contraction in human and rat pulmonary arteries.

The effect of hypoxia was investigated in human (HPA) and rat (RPA) pulmonary arteries. Hypoxia-induced contraction was 95 +/- 8.7% and 9.3 +/- 4.8% of the control response to K(+)-rich (80 mM) solution in HPA and RPA, respectively (n = 10). When RPA strips were precontracted with phorbol 12,13 dibutyrate (0.2 microM), hypoxia elicited a larger contraction (105 +/- 13.4% of the control response, n = 8). In both types of artery, hypoxia-induced contraction was dependent on the extracellular calcium concentration (66 +/- 8.4% and 40 +/- 14.4%, reduction for 1.25 mM Ca2+ in HPA and RPA, respectively, n = 6) and was inhibited by verapamil (0.05-10 microM) and nifedipine (0.05-1 microM). Glibenclamide (5-10 microM) increased the amplitude of hypoxia-induced contraction (+42 +/- 5.3%, n = 5). Hypoxia-induced contraction was blocked by cromakalim (1 microM) and this effect was reversed by glibenclamide (5 microM). This contraction was also inhibited by iodoacetic acid (250 microM). In beta-escin skinned pulmonary arterial strips, hypoxia had no effect on the calcium concentration-tension relationship. These results suggest that the O2 sensor in the pulmonary artery is located on the vascular smooth muscle plasmalemma. Hypoxia-induced contraction is dependent on calcium influx through voltage sensitive calcium channels. Its amplitude is modulated by the functioning of potassium channels.

Aged↗
PubMed1995

Role of protein kinase C in nonsensitized and passively sensitized human isolated bronchial smooth muscle.

To examine the role of protein kinase C (PKC) activation in the control of the mechanical activity of human isolated bronchial smooth muscle obtained at thoracotomy, the effect of the phorbol ester phorbol 12,13-dibutyrate (PDB) was evaluated. PDB produced slowly developing and sustained contractions that were reduced 1) by the PKC inhibitor staurosporine and 2) after long-term (12 h) exposure to PDB, which downregulates PKC. Moreover, the inactive phorbol ester 4 alpha-phorbol 12,13 didecanoate had no contractile effect. Removal of external Ca2+ or addition of the Ca(2+)-channel antagonist verapamil reduced the PDB-induced contraction. Passive sensitization of human isolated bronchial rings, i.e., incubation overnight of tissues in serum from atopic asthmatic patients, decreased the maximal response to PDB to 28.9 +/- 8% of the maximal response to acetylcholine (ACh) when compared with that of paired nonsensitized rings, i.e., tissues incubated overnight in serum from normal subjects (46.7 +/- 9.4% of the maximal response to ACh, n = 5, P < 0.05). The decrease in the response to PDB induced by either long-term preexposure to PDB or passive sensitization was reversed when both types of tissues were allowed to recover unstimulated for 3 h before PDB application. These results show that 1) PKC activation induces maintained contractions in human isolated airway smooth muscle that are largely dependent on extracellular calcium; 2) passive sensitization alters the PKC-mediated response in a way similar to that induced by prolonged stimulation of PKC.

Alkaloids↗