Effect of 2,3-butanedione monoxime on smooth-muscle contraction of guinea-pig portal vein

Inhibitors of myosin, but not actin, alter transport through Tradescantia plasmodesmata

Actin and myosin are components of plasmodesmata, the cytoplasmic channels between plant cells, but their role in regulating these channels is unclear. Here, we investigated the role of myosin in regulating plasmodesmata in a well-studied, simple system comprising single filaments of cells which form stamen hairs in Tradescantia virginiana flowers. Effects of myosin inhibitors were assessed by analysing cell-to-cell movement of fluorescent tracers microinjected into treated cells. Incubation in the myosin inhibitor, 2,3-butanedione monoxime (BDM) or injection of anti-myosin antibodies increased cell-cell transport of fluorescent dextrans, while treatment with the myosin inhibitor N-ethylmaleimide (NEM) decreased cell-cell transport. Pretreatment with the callose synthesis inhibitor, deoxy-D: -glucose (DDG), enhanced transport induced by BDM treatment or injection of myosin antibodies but did not relieve NEM-induced reduction in transport. In contrast to the myosin inhibitors, cell-to-cell transport was unaffected by treatment with the actin polymerisation inhibitor, latrunculin B, after controlling for callose synthesis with DDG. Transport was increased following azide treatment, and reduced after injection of ATP, as in previous studies. We propose that myosin detachment from actin, induced by BDM, opens T. virginiana plasmodesmata whereas the firm attachment of myosin to actin, promoted by NEM, closes them.

Regulatory mechanism of smooth muscle contraction studied with gelsolin-treated strips of taenia caeci in guinea pig

The potential roles of the regulatory proteins actin, tropomyosin (Tm), and caldesmon (CaD), i.e., the components of the thin filament, in smooth muscle have been extensively studied in several types of smooth muscles. However, controversy remains on the putative physiological significance of these proteins. In this study, we intended to determine the functional roles of Tm and CaD in the regulation of smooth muscle contraction by using a reconstitution system of the thin filaments. At appropriate conditions, the thin (actin) filaments within skinned smooth muscle strips of taenia caeci in guinea pigs could be selectively removed by an actin-severing protein, gelsolin, without irreversible damage to the contractile apparatus, and then the thin filaments were reconstituted with purified components of thin filaments, i.e., actin, Tm, and CaD. We found that the structural remodeling of actin filaments or thin filaments was functionally linked to the Ca2+-induced force development and reduction in muscle cross-sectional area (CSA). That is, after the reconstitution of the gelsolin-treated skinned smooth muscle strips with pure actin, the Ca2+-dependent force development was partially restored, but the Ca2+-induced reduction in CSA occurred once. In contrast, the reconstitution with actin, followed by Tm and CaD, restored not only the force generation but also both its Ca2+sensitivity and the reversible Ca2+-dependent reduction in CSA. We confirmed that both removal of the thin filaments by gelsolin treatment and reconstitution of the actin (thin) filaments with Tm and CaD caused no significant changes in the level of myosin regulatory light chain phosphorylation. We thus conclude that Tm and CaD are necessary for the full regulation of smooth muscle contraction in addition to the other regulatory systems, including the myosin-linked one.

Adenosine receptor-mediated coronary vascular protection in post-ischemic mouse heart

This study evaluated the ability of A1 and A3 adenosine receptor (AR) agonism, and A1, A2A, A2B and A3AR antagonism (revealing "intrinsic" responses), to modify post-ischemic coronary dysfunction in mouse heart. Vascular function was assessed before and after 20 min global ischemia and 30-45 min reperfusion in Langendorff perfused C57/Bl6 mouse hearts. Ischemic insult impaired coronary sensitivity to the endothelial-dependent dilators ADP (pEC50=6.8+/-0.1 vs. 7.6+/-0.1, non-ischemic) and acetylcholine (pEC50=6.1+/-0.1 vs. 7.3+/-0.1 in non-ischemic), and for the mixed endothelial-dependent/independent dilator 2-chloroadenosine (pEC50=7.5+/-0.1 vs. 8.4+/-0.1, non-ischemic). Endothelium-independent dilation in response to nitroprusside was unaltered (pEC50=7.0+/-0.1 vs. 7.1+/-0.1 in non-ischemic). Pre-treatment with a selective A1AR agonist (50 nM CHA) failed to modify coronary dysfunction, whereas A1AR antagonism (200 nM DPCPX) worsened the effects of I/R (2-chloroadenosine pEC50=6.9+/-0.1). Conversely, A3AR agonism (100 nM Cl-IB-MECA) did reduce effects of I/R (pEC50s=8.0+/-0.1 and 7.3+/-0.1 for 2-chloroadenosine and ADP, respectively), whereas antagonism (100 nM MRS1220) was without effect. While A2AAR agonism could not be assessed (due to pronounced vasodilatation), A2AAR antagonism (100 nM SCH58261) was found to exert no effect, and antagonism of A2BARs (50 nM MRS1754) was also ineffective. The protective actions of A3AR agonism were also manifest as improved reactive hyperemic responses. Interestingly, post-ischemic coronary dysfunction was also limited by: Na+-H+ exchange (NHE) inhibition with 10 or 50 microM BIIB-513 (2-chloroadenosine pEC50s=7.8+/-0.1, either dose), an effect not additive with A3AR agonism; Ca2+ antagonism with 0.3 microM verapamil (2-chloroadenosine pEC50=7.9+/-0.1); and Ca2+ desensitization with 5 mM BDM (2-chloroadenosine pEC50=7.8+/-0.1). In contrast, endothelin antagonism (200 nM PD142893) and anti-oxidant therapy (300 microM MPG+150 U/ml SOD+600 U/ml catalase) were ineffective. Our data collectively confirm that ischemia selectively impairs endothelial function and reactive hyperemia independently of blood cells. Vascular injury is intrinsically limited by endogenous (but not exogenous) activation of A1ARs, whereas exogenous A3AR activation further limits dysfunction (improving post-ischemic vasoregulation). Finally, findings suggest this form of post-ischemic coronary injury is unrelated to endothelin or oxidant stress, but may involve modulation of Ca2+ overload and/or related ionic perturbations.

Brief pretreatment of radial artery conduits with phenoxybenzamine prevents vasoconstriction long term

BACKGROUND

Radial artery bypass conduits are prone to early vasospasm or "string sign" with use of vasopressor therapy intraoperatively and postoperatively, causing increased resistance in coronary artery grafts. Current intraoperative treatment with papaverine fails to provide sustained inhibition of vasoconstriction. We tested the hypothesis that a 30-minute pretreatment of radial artery segments with the alpha-adrenergic antagonist phenoxybenzamine (PB) or the putative protein phosphatase 2,3-butadione monoxime (BDM) attenuates vasoconstriction induced by the vasopressors phenylephrine or norepinephrine for as long as 48 hours compared with papaverine.

METHODS

Canine radial arteries were harvested, incubated in control buffer or solutions of papaverine 10(-6) M, BDM 10(-6) M or phenoxybenzamine 10(-6) M for 30 minutes, washed, and stored in drug-free culture medium for 2, 24, or 48 hours. After storage, constriction was induced by norepinephrine at incremental concentrations ranging from 0.7 to 3.5 micromol/L or by phenylephrine (0.300 to 1.5 micromol/L) with or without the inhibitors, and the degree of vasoconstriction was quantified in organ chambers. Responses to norepinephrine or phenylephrine were compared to constriction with receptor-independent potassium chloride KC1 (30 mmol/L).

RESULTS

Maximum responses to phenylephrine and norepinephrine were comparable at 2, 24, and 48 hours after harvest in the control group (phenylephrine: 67% +/- 4%, 62% +/- 6%, 65% +/- 6% of KC1 response; norepinephrine: 75% +/- 4%, 62% +/- 1%, 58% +/- 7%, respectively). Papaverine failed to attenuate constriction to phenylephrine and norepinephrine 2, 24, or 48 hours posttreatment. Pretreatment with BDM did not reduce vasoconstriction responses to phenylephrine or norepinephrine 2 hours after incubation but did reduce constriction responses thereafter. In contrast, phenoxybenzamine completely attenuated constriction to both phenylephrine (19% +/- 8%, 1% +/- 4%, -12% +/- 4%) and norepinephrine (7.1% +/- 1%, -5% +/- 5%, -20% +/- 5%) at 2, 24, and 48 hours posttreatment, respectively. Phenoxybenzamine did not alter endothelial function relative to controls at any time point.

CONCLUSIONS

Thirty-minute pretreatment of RA conduits with 10(-6) M phenoxybenzamine completely inhibits vasoconstriction to phenylephrine and norepinephrine for as long as 48 hours. Soaking radial artery grafts briefly in phenoxybenzamine solution before implantation may be effective in preventing postoperative vasospasm caused by two common alpha-adrenergic agonists used in postoperative hemodynamic management.

Effect of butanedione monoxime on the contractility of guinea pig ileum and on the electrophysiological activity of myenteric S-type neurones

2,3-Butanedione monoxime (BDM) has demonstrated protective effects on isolated cardiac tissues, and on smooth muscle but its mechanism of action is not fully understood. To simultaneously study the effect of BDM on muscle contractility and on neuronal activity, the effect of BDM was tested in the contractile force of myenteric plexus-longitudinal muscle strips and in electrophysiological activity of myenteric S-type neurones of guinea pig ileum. BDM reduces, in a dose-dependent manner, the force of the spontaneous motility and the contractions induced by acetylcholine, bethanechol and electrical stimulation. The same BDM concentrations depolarize the neuronal membrane and reduce the rate of evoked firing. The effect of BDM can be attributed to a direct effect on the smooth muscle and to modifications of the neuronal activity.

Force-inhibiting effect of okadaic acid on skinned rat uterus permeabilized with alpha-toxin

Effects of okadai acid (OA) on contractile force in rat uterine uterine muscles permeabilized with alpha-toxin were examined. (1) Contractile force activated by Ca2+(10(-6.5) M to 10(-4.4) M) was suppressed by relatively low concentrations of OA (30 to 300 nM). The suppressed force was further decreased after washed out of OA. (2)Addition of 10 microM OA enhanced force. Whereas, the increased tension level fell to less than the control level after washed out of OA. (3)Okadaic acid methyl ester (methyl okadaate), an OA derivative without protein phosphatase inhibition, did not affect contraction. These results suggest that the force-inhibiting effect of OA is a result of interference with contractile elements through inhibition of protein phosphatases (PPs) activity.

Comparison of the effects of 2,3-butanedione monoxime on force production, myosin light chain phosphorylation and chemical energy usage in intact and permeabilized smooth and skeletal muscles

The primary goal of this study was to determine the utility of 2,3-butanedione monoxime as a tool for determining and separating the chemical energy usage associated with force production from that of force-independent, or 'activation' processes in smooth and skeletal muscles. We determined the effects of 2,3-butanedione monoxime on force production, myosin light chain phosphorylation and high energy phosphate usage in intact and permeabilized smooth (rabbit taenia coli) and skeletal (mouse extensor digitorum longus) muscles. In the intact taenia coli, 2,3-butanedione monoxime depressed the tonic phase of the tetanus, contractures evoked by high potassium (90 mM) and by carbachol (10(-5) M) and the small force response evoked by these agonists after treatment with D-600 (10(-5) M). In the electrically stimulated intact taenia coli 2,3-butanedione monoxime (0-20 mM) caused a proportional inhibition of tetanic force output, myosin light chain phosphorylation and high energy phosphate usage (ED50 approximately 7 mM for all these parameters). At 20 mM 2,3-butanedione monoxime, force and energy usage fell to near zero and the degree of myosin light chain phosphorylation decreased to resting values, indicating a shut-down of both force-dependent and force-independent energy usage at high concentrations of 2,3-butanedione monoxime. In permeabilized taenia coli, 2,3-butanedione monoxime had little or no depressant effects on force production, ATPase activity or calcium sensitivity. 2,3-butanedione monoxime had a very modest inhibitory effect on the in vitro motility of unregulated actin filaments interacting with thiophosphorylated myosin. In solution, 2,3-butanedione monoxime inhibited myosin light chain kinase, but not the phosphatase (SMP-IV). These results suggest that the major effect of 2,3-butanedione monoxime is not on the contractile proteins themselves, but rather on calcium delivery during excitation, thereby reducing the degree of activation of myosin light chain kinase and subsequent activation of myosin by light chain phosphorylation. Thus, 2,3-butanedione monoxime is not useful for the determination of the energetics of activation processes in smooth muscle because of its inhibition of both force-dependent and force-independent processes. In contrast, in the intact mouse extensor digitorum longus, 2,3-butanedione monoxime inhibits tetanic force production (ED50 approximately 2 mM) to a much greater extent than myosin light chain phosphorylation. When 2,3-butanedione monoxime was used to manipulate force production in muscles at L(o), it was found that approximately 60% of the total energy usage was force-independent and the remainder was force-dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of 2,3-butanedione monoxime on smooth-muscle contraction of guinea-pig portal vein

Effects of 2,3-butanedione-2-monoxime (BDM) on the contraction of intact and skinned smooth muscles from guinea-pig portal vein were examined. In intact preparations loaded with fura-2, 5-10 mM BDM markedly suppressed Ca2+ transients and force developments induced by 154 mM potassium and by phenylephrine (0.1 mM). On the other hand, in Ca(2+)-free depolarizing solution, BDM did not suppress phenylephrine (0.1 mM)-induced Ca2+ transient and force development. In skinned preparations obtained with Staphylococcus aureus alpha-toxin treatment, BDM did not markedly affect active force development. The above results indicate that BDM suppresses contraction of the portal vein mainly by the inhibition of voltage-dependent cytosolic Ca2+ transients. An additional result suggests that BDM suppresses the force-enhancing effect of alpha 1-adrenergic agents on the contractile elements.