Airway smooth muscle as a target of asthma therapy: history and new directions

Ultimately, asthma is a disease characterized by constriction of airway smooth muscle (ASM). The earliest approach to the treatment of asthma comprised the use of xanthines and anti-cholinergics with the later introduction of anti-histamines and anti-leukotrienes. Agents directed at ion channels on the smooth muscle membrane (Ca(2+ )channel blockers, K(+ )channel openers) have been tried and found to be ineffective. Functional antagonists, which modulate intracellular signalling pathways within the smooth muscle (β-agonists and phosphodiesterase inhibitors), have been used for decades with success, but are not universally effective and patients continue to suffer with exacerbations of asthma using these drugs. During the past several decades, research energies have been directed into developing therapies to treat airway inflammation, but there have been no substantial advances in asthma therapies targeting the ASM. In this manuscript, excitation-contraction coupling in ASM is addressed, highlighting the current treatment of asthma while proposing several new directions that may prove helpful in the management of this disease

TLR1/2 Activation during Heterologous Prime-Boost Vaccination (DNA-MVA) Enhances CD8+ T Cell Responses Providing Protection against Leishmania (Viannia)

Leishmania (Viannia) are the predominant agents of leishmaniasis in Latin America. Given the fact that leishmaniasis is a zoonosis, eradication is unlikely; a vaccine could provide effective prevention of disease. However, these parasites present a challenge and we do not fully understand what elements of the host immune defense prevent disease. We examined the ability of vaccination to protect against L. (Viannia) infection using the highly immunogenic heterologous prime-boost (DNA-modified vaccinia virus) modality and a single Leishmania antigen (TRYP). Although this mode of vaccination can induce protection against other leishmaniases (cutaneous, visceral), no protection was observed against L. (V.) panamensis. However, we found that if the vaccination was modified and the innate immune response was activated through Toll-like receptor1/2(TLR1/2) during the DNA priming, vaccinated mice were protected. Protection was dependent on CD8 T cells. Vaccinated mice had higher CD8 T cell responses and decreased levels of cytokines known to promote infection. Given the long-term persistence of CD8 T cell memory, these findings are encouraging for vaccine development. Further, these results suggest that modulation of TLR1/2 signaling could improve the efficacy of DNA-based vaccines, especially where CD8 T cell activation is critical, thereby contributing to effective and affordable anti parasitic vaccines

Internal calcium stores and norepinephrine overflow from isolated, field stimulated rat vas deferens

Ryanodine has been shown to selectively inhibit the initial phase of contraction of rat vas deferens smooth muscle stimulated by endogenous release of norepinephrine (NE) (1), and part of this effect could be pre-junctional. To assess this, its effect on NE overflow was measured in the same preparation. NE overflow from electrical field-stimulated isolated rat vas deferens was quantified by electrochemical detection using HPLC. In order to limit pre-junctional autoregulatory mechanisms, α2-adrenergic receptors were blocked and P(2x) purinergic receptors were desensitized. In these experimental conditions, NE overflow was directly proportional to extracellular Ca2+ concentration. Ryanodine only induced a modest decrease in NE overflow. Cyclopiazonic acid (CPA), an inhibitor of sarcoplasmic reticulum Ca2+-ATPase, slightly increased NE overflow but decreased smooth muscle contraction induced by electrical field stimulation. It is concluded that part of the effect of ryanodine on field stimulation-induced contraction may be due to an inhibition of NE release, although the major inhibitory effect of this alkaloid is post junctional. For CPA, its inhibitory effect on field stimulation-induced contraction is entirely postjunctional. Its effect on NE overflow suggests that, in this preparation, internal Ca2+ stores could function to accelerate termination of neurotransmitter release by sequestering cytosolic Ca2+.link_to_subscribed_fulltex

Access of extracellular calcium to internal stores in permeabilized bovine trachealis smooth muscle

Symposium Lecture no.

Cardiac and vascular effects of nitric oxide synthase inhibition in lipopolysaccharide-treated rats

In the present study, intraperitoneal injection of lipopolysaccharide (10 mg/kg) to anaesthetized rats produced a gradual fall in mean arterial pressure in 6 h. Aortic rings from lipopolysaccharide-treated rats showed a significant reduction in the contractile response to vasoconstrictors. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME) or aminoguanidine, two nitric oxide synthase (NOS) inhibitors, abolished this vascular hyporeactivity. In ventricular myocytes isolated from lipopolysaccharide-treated rats, both electrically induced Ca2+ transients and the intracellular Ca2+ response to β-adrenergic stimulation were significantly depressed when compared with those recorded from myocytes from sham control rats. L-NAME and aminoguanidine alone had no effects on electrically stimulated Ca2+ transients in ventricular myocytes either from control or lipopolysaccharide-treated rats. However, these two NOS inhibitors augmented the intracellular Ca2+ response to β-adrenergic stimulation in myocytes from lipopolysaccharide-treated rats, but not in control myocytes. In addition, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of nitric oxide (NO)-sensitive guanylyl cyclase, also reversed the intracellular Ca2+ hyporesponsiveness to β-adrenergic stimulation in myocytes from lipopolysaccharide-treated rats. In cardiac myocytes from lipopolysaccharide-rats pretreated with aminoguanidine, the intracellular Ca2+ hyporesponsiveness to β-adrenergic stimulation was abolished. However, there still existed a depressed Ca2+ response to electrical field stimulation. These data indicate that NO following lipopolysaccharide stimulation contributes to vascular hyporeactivity and the depressed intracellular Ca2+ response to β-adrenergic stimulation in lipopolysaccharide-treated rats, but is not responsible for the reduced Ca2+ response to electrical stimulation in our experimental conditions. (C) 2000 Elsevier Science B.V.link_to_subscribed_fulltex

Relationship between muscarinic receptor reserve and mode of excitation-contraction coupling in Bovine tracheal smooth muscle

Symposium Lecture no.