摘要:

In 1925, Wilson listed, in his classic third edition ofCell in Development and Heredity, four theories for the morphological and physiological characteristics of cytoplasm; each theory provided some sort of explanation as to the mechanism(s) of organelle translocations. During the past twenty years, cell biologists have focused their attentions on the cell's cytoskeleton, microtrabecular lattice, and associated mechanochemical motors which drive organelles along cytoskeletal tracks. A number of cell types have been used to study organelle translocations, but chromatophores, pigment cells, from cold‐blooded vertebrates have been one of the more popular models. This article reviews some of the research findings during the past twenty years, particularly those involving cytoplasmic elements: i.e, microfilaments, intermediate filaments, microtubules, and mechanochemical motors. In addition, it contrasts the proposed involvement of these elements in organelle translocations with the endoplasmic reticulum, a tubulovesicular organelle, which we recently demonstrated is responsible, through its elongation or retraction, for the translocations of carotenoid droplets in goldfish xanthophores and swordtail fish erythrophores. Here, the carotenoid droplets are not free in the cytoplasm and do not translocate via cytoskeletal tracks, but instead are attached to or are a part of the endoplasmic reticulum. On the other hand, carotenoid droplets of squirrel fish erythrophores are free in the cytoplasm and appear to translocate via microtubules. Finally, the rates of pigmentary organelle translocations are reviewed in light of the participation of the cytoskeletal elements with the endoplasmic reticulu

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1992.tb00001.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Dihydroxybenzoic acids (DBA), such as 3,4‐DRA, 3,5‐DBA, and 2,4‐DBA—at all concentrations tested—inhibited the rate of DL‐DOPA oxidation to dopachrome (λmax = 475 nm) by mushroom tyrosinase. 2,3‐DBA and 2,5‐DBA at relatively low concentration had a synergistic effect on the reaction, whereas at relatively high concentrations they inhibited the rate of DL‐DOPA oxidation. The synergistic effect of 0.6‐13.3 mM 2,3‐DRA on the rate of DL‐DOPA oxidation to dopachrome (λmax = 475 nm) was found to be due to the ability of 2,3‐DBA‐o‐quinone (formed by the oxidation of 2,3‐DBA by mushroom tyrosinase or by sodium periodate) to oxidize DL‐DOPA to dopachrome (via dopaquinone) non‐enzymatically. A similar explanation is likely to be valid for the synergism exerted by 2,5‐DBA on the rate of D

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1992.tb00002.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The levels of some catecholamine metabolites, namely homovanillic acid (HVA), vanil‐mandelic acid (VMA), 3‐methoxytyramine (MT), normetanephrine (NMN), metanephrine (MN), 3,4‐dihydroxy mandelic acid (DOMAC), and 3,4‐dihydroxy phenylacetic acid (DOPAC), have been evaluated in the 24 hr urines of 150 patients affected with different types of vitiligo and in 50 healthy age‐matched individuals. The patients were divided into three groups according to the different phases of the disease. The first group included subjects affected either with the early active phase or with progressive increase in both number and/or the size of previous lesions. The second group included patients in whom no new lesions had appeared for between 4‐8 months. In the third group the white areas had been stable for 1‐5 years. The first and second groups showed values of HVA and VMA from 4 to 10 times and from ½ to 3 times higher respectively than those of controls, while no significant differences were found between the third group and controls. Our results clearly show that a significant increase of urinary levels of HVA and VMA, deriving respectively from dopamine and from norepinephrine and epinephrine characterizes the onset and the progressive active phases of vitiligo, irrespective of the type of distribution. The increased release of catecholamines from the autonomic nerve endings in the microenvironment of melanocytes in the affected skin areas might be involved in the etiopathogenesis of vitiligo through two main mechanisms: (1) a direct cytotoxic action of catecholamines and/or their o‐diphenol catabolites; (2) an indirect action. Skin and mucosa arterioles possess α receptors, activation of which by catecholamine discharge may cause a severe vasoconstriction, leading to epidermal and dermal hypoxia with hyperproduction of toxic oxyradicals generated by different pathways. In both cases a genetic predisposition due to insufficient radical scavengers in the affected areas should be t

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1992.tb00003.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1992.tb00004.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY