摘要:

In smooth muscle it is generally accepted that at the level of the contractile apparatus regulation is achieved by activating a dormant state in the presence of Ca2+. This event initiates the contractile process which is manifest by an increased cross-bridge cycling rate and the development of tension, or in biochemical terms, by an increase in the activation by actin of the Mg2+-ATPase activity of myosin. A controversy exists, however, on the identity of the activator, and this review considers the two proposed possibilities. One theory is based on the phosphorylation and dephosphorylation of the 20,000 dalton molecular weight myosin light chains. It is assumed that in the phosphorylated state the Mg2+-ATPase activity of myosin can be activated by actin whereas dephosphorylated myosin cannot be activated by actin. Phosphorylation of myosin, and hence the activation of the contractile apparatus, is achieved by a myosin light chain kinase, and it has been shown that the calcium dependence of the phosphorylation reaction resides with one of the two components of this enzyme, namely calmodulin. Inactivation of the contractile apparatus is brought about by a second enzyme, the myosin light chain phosphatase. There is considerable experimental evidence in support of the phosphorylation theory and it appears that it must be at least a part of the regulatory system. However, it cannot be concluded that phosphorylation-dephosphorylation of myosin is the sole regulatory mechanism, and recent results have indicated that additional factors may be involved. The second theory to account for the activation of the contractile apparatus is not based on the phosphorylation of the myosin molecule and is thought to be due to a system called leiotonin. This system, composed of two subunits leiotonin A and C, is thought to be associated with the thin filaments. Its mode of action has not been established.

ISSN:1018-1172    

DOI:10.1159/000158369

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

Finite deformations and stresses in vascular walls are studied analytically in the paper. Nonlinear viscoelastic constitutive relations suitably modified for the consideration of the anisotropic behavior of the vessel walls are used in the analysis. The time dependence of the inner surface and the force exerted by the surrounding connective tissues are also taken into account. Using approximations for short time ranges, a quantitative analysis is made in order to illustrate the applicability of the analytical study.

ISSN:1018-1172    

DOI:10.1159/000158370

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

Previous studies have shown that transmural electrical stimulation (TES) of the rabbit portal vein in vitro, results in the overflow of 3H-purines from tissues prelabelled with 3H-adenosine. The purpose of the present study was to assess the possible sites which contribute to the TES-induced overflow of purines in this adrenergically innervated tissue. The contribution of postjunctional elements to purine overflow was assessed with the α1-adrenoceptor antagonist, prazosin. Prazosin (3 × 10–7 M) did not affect the release of 3H-norepinephrine but markedly reduced the TES-induced contraction. The release of 3H-purines was reduced by 20% by prazosin, indicating that approximately 80% of the release is independent of the α1-mediated postjunctional response and, therefore, probably originates from neuronal sites in the tissue. Two lines of evidence indicate that a considerable portion of the α1-adrenoceptor-independent release of 3H-purines (i.e., in the presence of prazosin) arises from adrenergic nerves. First, the fractional release of 3H-purines was enhanced and reduced, respectively, by the α2-adrenoceptor antagonist, yohimbine, and the α2-adrenoceptor agonist, clonidine, in concentrations (10–6 M) which did likewise to the fractional release of 3H-norepinephrine. Second, destruction of the adrenergic nerves by in vitro treatment with 6-hydroxydopamine reduced the fractional release of 3H-purines by 55 %. The release of purines which remains after 6-hydroxydopamine treatment may occur from non-adrenerg

ISSN:1018-1172    

DOI:10.1159/000158371

出版商:S. Karger AG    

年代:1982

数据来源: Karger

摘要:

Quantitative image analysis of fluorescent nerves following histochemical localization of monoamines in stretch preparations of the rabbit ear artery (REA) reveals marked differences in the density of innervation between the proximal and distal regions. The innervation in the proximal region is about twice as dense as that in the distal region and there are approximately 10,500 and 6,500 varicosities per mm2 vessel area in these two regions, respectively. These varicosities have approximately the same mean diameter throughout the length of the vessel. The noradrenaline contents per gram wet weight of tissue in the proximal and distal regions are 1.93 and 0.94 µg, respectively. It is estimated that noradrenaline contents per mm2 nerve plexus area are 0.30 and 0.08 ng and that the nerve endings contain 2.8 × 10–14 and 1.2 × 10–14 g per varicosity in the proximal and distal REA, respectively. Sympathetic nerve stimulation in vitro with frequencies up to 8 Hz elicits larger and faster contractions in the proximal REA and the threshold frequency is less than in the distal region. This study also indicates that care should be taken to use the same region when using the REA for pharmacological and physiological s

ISSN:1018-1172    

DOI:10.1159/000158372

出版商:S. Karger AG    

年代:1982

数据来源: Karger