On the mechanism of the persistent action of salmeterol: what is the current position?

The mechanism of the long duration of action of salmeterol at β₂-adrenoceptors has long been a matter of debate, and is still unresolved. Szczuka and colleagues have both summarized the position to date and suggested a new mechanistic contender, receptor rebinding. Despite this, they still do not come to any clear conclusion. Much of the literature data that they have drawn upon appears contradictory, and mathematical models are inevitably flawed by the questionable validity of key values applied to them. Although the issue will undoubtedly eventually be resolved, it will probably require investigators to apply carefully designed studies on simple experimental systems such as isolated membranes or cultured cells. Only then should studies be extended to more complex systems such as isolated preparations of airways smooth muscle, where tissue bulk inevitably presents a complicating factor, particularly where relatively lipophilic compounds are concerned.     

Comparison of mechanical and electrical activity and interstitial cells of Cajal in urinary bladders from wild-type and W/Wv mice

Background and purpose:

W/W^v and wild-type murine bladders were studied to determine whether the W/W^v phenotype, which causes a reduction in, but not abolition of, tyrosine kinase activity, is a useful tool to study the function of bladder interstitial cells of Cajal (ICC).

Experimental approach:

Immunohistochemistry, tension recordings and microelectrode recordings of membrane potential were performed on wild-type and mutant bladders.

Key results:

Wild-type and W/W^v detrusors contained c-Kit- and vimentin-immunopositive cells in comparable quantities, distribution and morphology. Electrical field stimulation evoked tetrodotoxin-sensitive contractions in wild-type and W/W^v detrusor strips. Atropine reduced wild-type responses by 50% whereas a 25% reduction occurred in W/W^v strips. The atropine-insensitive component was blocked by pyridoxal-5-phosphate-6-azophenyl-2′,4′-disulphonic acid in both tissue types. Wild-type and W/W^v detrusors had similar resting membrane potentials of −48 mV. Spontaneous electrical activity in both tissue types comprised action potentials and unitary potentials. Action potentials were nifedipine-sensitive whereas unitary potentials were not. Excitatory junction potentials were evoked by single pulses in both tissues. These were reduced by atropine in wild-type tissues but not in W/W^v preparations. The atropine-insensitive component was abolished by pyridoxal-5-phosphate-6-azophenyl-2′,4′-disulphonic acid in both preparations.

Conclusions and implications:

Bladders from W/W^v mice contain c-Kit- and vimentin-immunopositive ICC. There are similarities in the electrical and contractile properties of W/W^v and wild-type detrusors. However, significant differences were found in the pharmacology of the responses to neurogenic stimulation with an apparent up-regulation of the purinergic component. These findings indicate that the W/W^v strain may not be the best model to study ICC function in the bladder.     

Visual identification of bacterially contaminated red cells

There have been increasing numbers of reports of transfusion-acquired Yersinia enterocolitica bacteremia (including several fatal cases). Fifteen units of whole blood were inoculated with various concentrations of Y. enterocolitica serotype 0:3 and processed into AS-3 preserved red cells (RBCs). Consistent growth of the organism was found at inoculum concentrations greater than or equal to 10 colony-forming units per mL. In all 13 units of RBCs that supported the growth of Y. enterocolitica, a darkening in color (due to hemolysis and a decrease in pO2) was observed in the bag. The attached sample segments, which were sealed from the main unit, remained sterile and did not darken. This color change was apparent in all the contaminated units by Day 35, which was 1.5 to 2 weeks after the bacteria were first detected in cultures of the blood. Hence, by comparison of the color of the segment tubing with that of the unit itself, units grossly contaminated with Y. enterocolitica can be identified prior to transfusion. Moreover, review of photographs on file at the Centers for Disease Control revealed this dramatic color change in 2 units of blood that caused transfusion-transmitted sepsis (Enterobacter agglomerans and an unidentified gram-negative bacillus, not Yersinia sp.), which demonstrated that the color change was not limited to Y. enterocolitica. This method of visual identification of contaminated units of blood could decrease the incidence of posttransfusion bacterial sepsis.     

Precocious expression of T cell functional response genes in vivo in primitive thymocytes before T lineage commitment

The genes encoding effector molecules of mature T cells, IL-2, perforin and IL-4, were found to be expressed in vivo in the most primitive subsets of thymocytes of adult mice. These subsets have previously been identified by their cell surface markers and by their expression of other T lineage-associated genes. While IL-2, perforin and IL-4 are expressed in distinct patterns, all three are expressed before the induction of RAG-1 and pre-TCR alpha mRNA expression, and are confined to subsets of cells that apparently have not yet undergone commitment to the T lineage. Thus, expression of T cell response genes appears to be one of the earliest markers of lymphocyte differentiation. Activation events marked by CD69 induction occur in these early cell types, but the response gene expression by these cells is separable from CD69 expression. IL-2 and perforin are induced again much later in thymocyte development, during TCR-dependent repertoire selection. At those stages, IL-2 protein and RNA levels per cell are higher, but the fraction of cells expressing IL-2 appears to be much lower than in the most immature stages. In addition, a striking feature of the immature populations is the robust IL-2 expression by presumptive immature NK cells. These findings are discussed in terms of the developmental origins of lineage specificity in T cell response gene regulation.      

Etiology of AIDS-related Kaposi's sarcoma and lymphoma

Kaposi's sarcoma (KS) and non-Hodgkin's lymphomas (NHL) are common consequences of HIV infection. These tumours appear to be precipitated by herpesviruses. Epstein-Barr virus (EBV) is implicated as a cause of up to 50% of systemic NHLs and up to 100% of central nervous system lymphomas in patients with AIDS. KS may be a consequence of the newly identified gamma-herpesvirus KSHV (KS-associated herpesvirus or HHV-8). This herpesvirus is found in all KS biopsies from different epidemiologic forms of this disease. KSHV is also implicated in the pathogenesis of a rare form of B cell lymphoma called body-cavity based lymphoma or primary effusion lymphoma (PEL).     

Normal and stenotic renal arteries: experimental balloon-expandable intraluminal stenting

Elastic recoil of the vessel wall is a common cause of failure of percutaneous transluminal angioplasty in renal arteries. To oppose such recoil, balloon-expandable metal stents were implanted in artificially stenotic renal arteries in pigs and normal renal arteries in dogs and pigs. The stents were then examined angiographically and histologically at regular intervals. All stents were completely covered with endothelialized neointima in 3 weeks. There was no difference in intimal thickness between the stenotic and nonstenotic renal arteries. A large stent diameter and a large open or nonmetal surface may cause less intimal hyperplasia, but nonturbulent, fast arterial flow is probably the most important factor in ensuring long-term patency of the vessel.