Cyclic nucleotide action is mediated through adenosine receptors in damselfish motile iridophores

Effects of cyclic nucleotides on motile iridophores were examined in the blue damselfish, Chrysiptera cyanea. All of the cyclic nucleotides tested, i.e. cAMP, 2',3'-cAMP and cGMP, accelerated the clearing response of the cells even at concentrations of 10(-5) or 10(-4) M. The action of these nucleotides was effectively antagonized by methylxanthines. These results suggest that the effect of cyclic nucleotides on damselfish iridophores is mediated by adenosine receptors in a similar fashion to the action of adenosine.     

Control of chromatophore movements in dermal chromatic units of blue damselfish--I. The melanophore

Mechanisms controlling pigment movements in the melanophore of the blue damselfish, Chrysiptera cyanea, were studied. Histological observations revealed that the melanophore had three-dimensionally developed processes to envelop overlying small iridophores, and thus participated in the construction of a simple dermal chromatophore unit. Nervous stimulation, catecholamines and melatonin brought about melanosome aggregation in the melanophore. The actions of the nervous stimulation and catecholamines were antagonized by alpha adrenolytic agents. A beta adrenergic agonist, metaproterenol, adenosine and adenine nucleotides, and alpha-MSH acted as pigment-dispersing agents. These results indicate that the melanophore of the present material is controlled quite orthodoxly by adrenergic nerves and endocrines, notwithstanding the fact that it has quite a unique morphology among fish species, and that its motile rate is remarkably high.     

Motile iridophores of a freshwater goby,Odontobutis obscura

Summary Reflecting chromatophores in the dermis of the skin of a freshwater goby, Odontobutis obscura, are of an iridophore type. These chromatophores contain numerous reflecting platelets, which are similar to those in iridophores of other fish and amphibian species. It was found that these iridophores are motile, i.e., these cells respond to certain stimuli with translocation of the platelets within the cells. K⁺ ions induced dispersion of the platelets in excised scale preparations, but not in excised scales from chemically denervated fish. Norepinephrine and melatonin also induced dispersion of the platelets. Alpha-MSH was effective in aggregating these organelles into the centrospheres of the cells. The conclusions reached are: (1) iridophores of O. obscura are motile; (2) the movement of the iridophores is under nervous and hormonal control.     

The involvement of calmodulin in motile activities of fish chromatophores

1. Effects of W-7 and W-5, calmodulin antagonists, on the pigment aggregation within melanophores and coloring response of iridophores were examined in the blue damselfish, Chrysiptera cyanea.2. W-7 was found to antagonize norepinephrine-induced responses of the chromatophores, whereas W-5 had only a slight effect on inhibition of the responses.3. H-7, a specific antagonist of protein kinase C, did not arrest the responses of melanophores and iridophores at all.4. The chromatophores responded normally to norepinephrine in Ca²⁺, Mg²⁺-free saline solution.5. These results indicate that it is a Ca²⁺/calmodulin-regulated enzyme and not protein kinase C that is involved in motile activities of fish chromatophores. Ca²⁺ may be supplied from an intracellular store.     

Ultrastructural observations of motile iridophores from the freshwater goby, Odontobutis obscura

The ultrastructure of "motile" iridophores of Odontobutis obscura and the changes in cell shape related to the motility were studied with electron microscopy. Various structural details were revealed by this method, and their importance is discussed. Of particular interest were the abundant microfilaments observed in the cortical cytoplasm. Cross-sectional profiles of iridophores showed that, in an iridophore in the dendritic state, the platelets were scattered randomly throughout the centrosphere and its processes, so that the centrosphere appeared to be rather flat. In the punctate state, the platelets were gathered, in groups or in stacks with regular arrangements, in the centrosphere, which appeared to be ovoid in shape. The most notable finding was that, at this time, the processes from which the platelets were lost remained there without retracting. The results indicates clearly that the motility of the goby iridophores involves the migration of platelets within the fixed contour of each cell and that no amoeboidal changes in the shapes of the cells occur.     

Effects of atropine on the melanophores and light-reflecting chromatophores of some teleost fishes

1. The mechanism of the action of atropine, which is known to accelerate the dispersion response of fish melanophores, was examined by use of various receptor antagonists.2. The effects of atropine were found to be independent of adenosine receptors, beta-adrenoceptors and MSH receptors on the melanophore membrane.3. Analogs of atropine, such as scopolamine, also had a potent pigment-dispersing effect on melanophores, whereas the quaternary ammonium derivatives, which are positively charged molecules, had only a small effect.4. These results suggest that the possible site of atropine action is within the chromatophores themselves.5. In addition to the melanosome-dispersing effect, atropine caused a shift in the spectral peak of reflected light toward shorter wavelengths and the dispersion of leucosomes in the motile iridophores of the blue damselfish and in the leucophores of the medaka, respectively.     

The Blue Coloration of the Common Surgeonfish, Paracanthurus hepatus-II. Color Revelation and Color Changes

Measurements of spectral reflectance from the sky-blue portion of skin from the common surgeonfish, Paracanthurus hepatus, showed a relatively steep peak at around 490 nm. We consider that a multilayer thin-film interference phenomenon of the non-ideal type, which occurs in stacks of very thin light-reflecting platelets in iridophores of that region, is primarily responsible for the revelation of that hue. The structural organization of the iridophore closely resembles that of bluish damselfish species, although one difference is the presence of iridophores in a monolayer in the damselfish compared to the double layer of iridophores in the uppermost part of the dermis of surgeonfish. If compared with the vivid cobalt blue tone of the damselfish, the purity of the blue hue of the surgeonfish is rather low. This may be ascribable mainly to the double layer of iridophores in the latter since incident lightrays are complicatedly reflected and scattered in the strata. The dark-blue hue of the characteristic scissors-shaped pattern on the trunk of surgeonfish is mainly due to the dense population of melanophores, because iridophores are only present there in a scattered fashion. Photographic and spectral reflectance studies in vivo, as well as photomicrographic, photo-electric, and spectrometric examinations of the state of chromatophores in skin specimens in vitro, indicate that both melanophores and iridophores are motile. Physiological analyses disclosed that melanophores are under the control of the sympathetic nervous and the endocrine systems, while iridophores are regulated mainly by nerves. The body color of surgeonfish shows circadian changes, and becomes paler at night; this effect may be mediated by the pineal hormone, melatonin, which aggregates pigment in melanophores.     

Rapid integumental color changes due to novel iridophores in the chameleon sand tilefish Hoplolatilus chlupatyi

The wavelength of the light reflected from iridophores depends on the thickness and the spacing of intracellular reflecting platelets. Here, we show that the rapid color change from blue to red of the chameleon sand tilefish Hoplolatilus chlupatyi is mediated by adrenergic stimulation of a novel type of iridophore in which reflecting platelets are concentrated selectively in the periphery of the cell, near the plasma membrane. The color changes are not only observed in vivo but also in pigment cells of isolated scales which respond to increases in K⁺ ion concentrations in 0.5 s and to addition of norepinephrine within 1 s. The norepinephrine effect can be blocked by addition of the alpha‐adrenergic antagonist phentolamine. The results suggest that adrenergic stimulation leads to changes in reflecting platelet organization in Hoplolatilus chlupatyi iridophores and represents the major mediator of the rapid color change in this fish in vivo.     

Cell-free synthesis of active ribulose-1,5-bisphosphate carboxylase in the mesophyll chloroplasts of Sorghum vulgare

In the presence of either methyl xanthines or adenosine deaminase, isoproterenol elicited large dramatic increases in accumulation of cyclic AMPP. In contrast, cyclic AMP accumulation in response to epinephrine or norepinephrine was not potentiated by either methyl xanthines or by adenosine deaminase. Blocking the alpha adrenergic activity of norepinephrine and epinephrine with phentolamine established synergism between these catecholamines and methyl xanthines and adenosine deaminase. The activity of the particulate phosphodiesterase was not influenced by norepinephrine suggesting that the lack of synergism between the catecholamines norepinephrine and epinephrine and methyl xanthines is unrelated to this enzyme. The data are interpreted to suggest that the alpha adrenergic activity of catecholamines prevents the potentiation of cyclic AMP accumulation that occurs when the action of endogenously produced adenosine is interfered with, either by its degradation with adenosine deaminase or by receptor blockade with methyl xanthine. Because a major action of adenosine on fat cells is to inhibit adenylate cyclase it is suggested that alpha adrenergic receptor activation limits the extent to which the enzyme adenylate cyclase can be activated in a fashion similar to that of adenosine.     

Interactions between catecholamines,methyl xanthines and adenosine in regulation of cyclic AMP accumulation in hamster adipocytes

In the presence of either methyl xanthines or adenosine deaminase, isoproterenol elicited large dramatic increases in accumulation of cyclic AMP. In contrast, cyclic AMP accumulation in response to epinephrine or norepinephrine was not potentiated by either methyl xanthines or by adenosine deaminase. Blocking the alpha adrenergic activity of norepinephrine and epinephrine with phentolamine established synergism between these catecholamines and methyl xanthines and adenosine deaminase. The activity of the particulate phosphodiesterase was not influenced by norepinephrine suggesting that the lack of synergism between the catecholamines norepinephrine and epinephrine and methyl xanthines is unrelated to this enzyme. The data are interpreted to suggest that the alpha adrenergic activity of catecholamines prevents the potentiation of cyclic AMP accumulation that occurs when the action of endogenously produced adenosine is interfered with, either by its degradation with adenosine deaminase or by receptor blockade with methyl xanthine. Because a major action of adenosine on fat cells is to inhibit adenylate cyclase it is suggested that alpha adrenergic receptor activation limits the extent to which the enzyme adenylate cyclase can be activated in a fashion similar to that of adenosine.     

Light-reflecting properties of the iridophores of the neon tetra,Paracheirodon innesi

• 1.1. The change in color of the lateral stripe of the neon tetra, Paracheirodon innesi, is due to the motile activity of the iridophores which are sensitive to light and adrenergic stimuli.
• 2.2. The light-reflecting platelets within the iridophore were found to be arranged regularly, making an acute angle of depression with respect to the median plane of the body.
• 3.3. When epi-illumination was applied to the skin piece laid horizontally on the stage of a light microscope (with an angle of incidence of about 40°) and the wavelength of the reflected light introduced into the objective lens was monitored, the spectral peak was found to shift to longer wavelengths with the application of K⁺-rich saline, with a simultaneous decrease in reflectance.
• 4.4. Using the identical fiber assembly for light irradiation and measurements of reflected light, we found that the angle of incident light producing the maximum reflectance, which corresponded to the inclination of the platelets, increased with the shift in the spectral peak toward longer wavelengths.
• 5.5. It appears from our results that a change in the angle of inclination of the platelets triggered by adrenergic stimuli may give rise to a change in the distance between the platelets which, in turn, leads to the shift in the spectral peak.

     

鳜皮肤图案中色素细胞的分布与排列

色素细胞是皮肤图案形成的基础,为了解鳜(Siniperca chuatsi)皮肤图案区域色素细胞的种类、分布及排列特征,采用光学显微镜与电子显微镜对鳜皮肤中图案区域、非图案区域及交界处皮肤的色素细胞进行显微及超显微结构观察。结果显示,鳜皮肤中含有黑色素细胞、黄色素细胞、红色素细胞及虹彩细胞,主要分布于表皮层和色素层。头部过眼条纹、躯干纵带、躯干斑块等图案区域皮肤表皮层与色素层均含有黑色素细胞,非图案区域仅表皮层含有少量黑色素细胞。躯干图案区域(纵带、斑块)皮肤色素层色素细胞分布层次明显,由外到内依次为黄色素细胞、红色素细胞、黑色素细胞和虹彩细胞,其中,虹彩细胞内反射小板较长,整齐水平排列;躯干非图案区域皮肤色素层由外到内依次为黄色素细胞、红色素细胞和虹彩细胞,其中,虹彩细胞内反射小板较短,无规则排列。头部过眼条纹色素层含有4种色素细胞,色素细胞数量较少,且无规则排列,其中,黑色素细胞内黑色素颗粒较大。交界处皮肤色素层黑色素细胞数量向非图案区域一侧逐渐减少,虹彩细胞数量逐渐增加。结果表明,鳜图案区域与非图案区域、不同图案区域的色素细胞分布与排列各不相同,本研究结果为鳜色素细胞图案化形成机制提供了基础资料。     

Malleable skin coloration in cephalopods: selective reflectance, transmission and absorbance of light by chromatophores and iridophores

Nature's best-known example of colorful, changeable, and diverse skin patterning is found in cephalopods. Color and pattern changes in squid skin are mediated by the action of thousands of pigmented chromatophore organs in combination with subjacent light-reflecting iridophore cells. Chromatophores (brown, red, yellow pigment) are innervated directly by the brain and can quickly expand and retract over underlying iridophore cells (red, orange, yellow, green, blue iridescence). Here, we present the first spectral account of the colors that are produced by the interaction between chromatophores and iridophores in squid (Loligo pealeii). Using a spectrometer, we have acquired highly focused reflectance measurements of chromatophores, iridophores, and the quality and quantity of light reflected when both interact. Results indicate that the light reflected from iridophores can be filtered by the chromatophores, enhancing their appearance. We have also measured polarization aspects of iridophores and chromatophores and show that, whereas structurally reflecting iridophores polarize light at certain angles, pigmentary chromatophores do not. We have further measured the reflectance change that iridophores undergo during physiological activity, from "off" to various degrees of "on", revealing specifically the way that colors shift from the longer end (infra-red and red) to the shorter (blue) end of the spectrum. By demonstrating that three color classes of pigments, combined with a single type of reflective cell, produce colors that envelop the whole of the visible spectrum, this study provides an insight into the optical mechanisms employed by the elaborate skin of cephalopods to give the extreme diversity that enables their dynamic camouflage and signaling.     

Apparent absence of alpha-2 adrenergic receptors from hamster brown adipocytes

The possible presence of α adrenergic control of lipolysis and cyclic AMP production in brown adipocytes of hamsters was studied in adipocytes isolated from interscapular, subscapular, cervical and axillary regions of normal male hamsters maintained at 25°C. Lipolysis activated by either 3-isobutyl-1-methyl xanthine or isoproterenol was unaffected by the presence of the α adrenergic selective agonists clonidine and methoxamine. Similarly, accumulation of cyclic AMP in response to β-receptor stimulation, alone or in combination with a methyl xanthine, was unaffected by clonidine or methoxamine. In contrast, both lipolysis and cyclic AMP accumulation in brown fat cells were effectively suppressed in the presence of nicotinic acid, prostaglandin E₁ or N⁶-phenylisopropyl adenosine. Accumulation of cyclic AMP in response to the mixed agonist norepinephrine was not influenced when cells were exposed to the alpha adrenergic blocking drugs yohimbine or tolazoline. These observations suggest that alpha-2 adrenergic receptors which are present on hamster white fat cells and control production of cyclic AMP and lipolysis are absent from hamster brown adipocytes. On the other hand, brown fat cells of this species appear to respond to a number of other inhibitory compounds in a manner not markedly different from that of white adipocytes.     

Alpha adrenergic receptor mediated formation of cyclic AMP in rat spinal cord

Methoxamine and phenylephrine (PE), postsynaptic alpha adrenergic agonists stimulated the accumulation of cyclic AMP in spinal cord tissue slices. Naphazoline, oxymetazoline and clonidine, previously shown to have greater efficacy at presynaptic alpha receptors did not alter accumulation and, in fact, blocked the PE response. The PE-stimulation was completely inhibited by postsynaptic alpha antagonists, incompletely by agents which bl ock presynaptic alpha receptors, and slightly by the beta blocker propranolol. Pe-stimulated accumulation was potentiated by phosphodiesterase inhibition (RO 20-1724). In contrast to previous reports on the requirement of the copresence of adenosine for alpha receptor stimulated accumulation of cyclic AMP in neuronal tissue, the PE-stimulation in spinal cord slices was unchanged by adenosine receptor blockade (theophylline), hydrolysis of endogenous adenosine (adenosine deaminase), inhibition of adenosine deaminase (EHNA) or blockade of adenosine uptake (dipyridamole). Added adenosine increased basal accumulation and produced a marked potentiation of the PE response. From this data it is evident that, in spinal cord tissue slices, there occurs a postsynaptic alpha adrenergic receptor linked to cyclic AMP accumulation which does not require the presence of other neurohumoral agents for activation.     

Influence of adenosine or adrenergic agonists on growth hormone stimulated lipolysis by chicken adipose tissue in vitro

In vitro lipolysis by chicken adipose explants was stimulated by growth hormone (GH) or glucagon. Adenosine or the adenosine agonist, N⁶-phenylisopropyladenosine (PIA), inhibited GH stimulated lipolysis, the effect of adenosine not being observed in the presence or adenosine deaminase. Glucagon induced lipolysis was also reduced by PIA. It is suggested that adenosine may act by G_i linked to either adenylate cyclase (for glucagon) or the signal transduction mechanism for GH. Lipolysis was not stimulated by GH in the presence of phenylephrine (α₁ adrenergic agonist), isoproterenol (β adrenergic agonist), adrenaline or glucagon. Although the presence of p-amino clonidine (α₂ adrenergic agonist) depressed basal lipolysis, a response to GH was still present. Either glucagon or β-adrenergic agonists (isoproterenol, adrenaline) stimulated lipolysis. In both cases, GH attenuated the lipolytic response to these hormones, which act via a cyclic adenosine monophosphate signal transduction mechanism.     

Light-sensitive motile iridophores and visual pigments in the neon tetra, Paracheirodon innesi

Although motile iridophores in the longitudinal stripes of neon tetra skin are under control of the sympathetic nervous system, they also respond to light directly and show circadian color changes. Using neon tetra skin, we found that the photoresponse of iridophores depends on light intensity, and that light near 500 nm is most effective. RT-PCR demonstrated the expression of mRNAs encoding rhodopsin and two kinds of cone opsins (Pi-green1 and Pi-green2) in neon tetra skin where the light-sensitive iridophores exist. These mRNAs are also expressed in the lateral eyes. The cone opsin genes, Pi-green1 and Pi-green2, show high similarity with the g101 and g103 genes of unique green cone opsins (belonging to the MWS/LWS group) of the blind Mexican cavefish. These results show that Pi-green1, Pi-green2, and/or rhodopsin may play important roles in the photoresponse of neon tetra iridophores, which are most sensitive to light near 500 nm.     

New insights regarding the regulation of chemotaxis by nucleotides, adenosine, and their receptors

The directional movement of cells can be regulated by ATP, certain other nucleotides (e.g., ADP, UTP), and adenosine. Such regulation occurs for cells that are "professional phagocytes" (e.g., neutrophils, macrophages, certain lymphocytes, and microglia) and that undergo directional migration and subsequent phagocytosis. Numerous other cell types (e.g., fibroblasts, endothelial cells, neurons, and keratinocytes) also change motility and migration in response to ATP, other nucleotides, and adenosine. In this article, we review how nucleotides and adenosine modulate chemotaxis and motility and highlight the importance of nucleotide- and adenosine-regulated cell migration in several cell types: neutrophils, microglia, endothelial cells, and cancer cells. We also discuss difficulties in conducting experiments and drawing conclusions regarding the ability of nucleotides and adenosine to modulate the migration of professional and non-professional phagocytes.     

Relationship between proton motive force and motility in Spirochaeta aurantia.

The effects of various metabolic inhibitors on the motility of Spirochaeta aurantia were investigated. After 15 min in sodium arsenate buffer, 90% of cells remained motile even though adenosine triphosphate levels dropped from 5.6 to 0.1 nmol/mg (dry weight) of cells. After 70 min in sodium arsenate, 5% of cells were motile. Addition of phenazine methosulfate plus ascorbate at this time resulted in motility of 95% of cells, but adenosine triphosphate levels remained at 0.1 nmol/mg of cell dry weight. Carbonyl cyanide-m-chlorophenyl hydrazone rapidly (within 1 min) and completely inhibited motility of metabolizing cells in potassium phosphate buffer. However, after 15 min in the presence of carbonyl cyanide m-chlorophenyl hydrazone the cellular adenosine triphosphate level was 3.4 nmol/mg (dry weight) of cells, and the rate of oxygen uptake was 44% of the rate measured in the absence of carbonyl cyanide m-chlorophenyl hydrazone. Cells remained motile under conditions where either the electrical potential or the pH gradient across the membrane of S. aurantia was dissipated. However, if both gradients were simultaneously dissipated, motility was rapidly inhibited. This study indicates that a proton motive force, in the form of either a transmembrane electrical potential or a transmembrane pH gradient, is required for motility in S. aurantia. Adenosine triphosphate does not appear to directly activate the motility system in this spirochete.     

Observations on the pigmentation of the pigeon iris

There are three genetically controlled iris types found in the pigeon, two of which contain stromal pigment cells, the third lacks pigment cells. The yellow (gravel) and white (pearl) iris types have pigment cells that contain birefringent pigment granules (crystals) and are ultrastructurally similar to iridophores of poikilothermic vertebrates. Both these iris types contain guanine as a major "pigment" and, in addition, the yellow iris contains at least two yellow fluorescing pigments that are tentatively identified as pteridines. The pigment cells of the yellow and white irises are structurally identical differing only in the presence or absence of these yellow pigments. The stromal pigment cells of the white iris correspond in structure and pigment chemistry to classical iridophores although they lack strong irridescence and are therefore perhaps best considered leucophores. The pigment cells of the yellow iris can be considered "reflecting xanthophores" having the combined properties of both classical xanthophores and iridophore/leucophores.