Binding of concanavalin A to secretory epidermis in the fish Blennius sanguinolentus pallas: light microscopic and ultrastructural studies

Concanavalin A (Con A) lectin from jack bean Canavalia ensiformis DC binds to alpha-D-glucopyranosyl and alpha-D-mannopyranosyl residues of the cuticular secretions (glycocalyx) attached to apical plasma membrane in the skin surface cells of Blennius sanguinolentus. The presence of Con A positive carbohydrate components is also observed in some secretory vesicles close under the apical cell membrane and in the goblet cell secretion spread over the surface of the skin. Other lectin labeling methods might offer a new tool for the cytochemical demonstration of glycoconjugates containing sugar residues on plasmic membranes of the epithelial cells. This can provide an insight into the functional significance of the carbohydrate moieties, attributable to the specialization of the cell membranes.     

Influence of lecithin acyl chain composition on the kinetics of exchange between chylomicrons and high density lipoproteins

The kinetics of lecithin exchange between native lipoproteins was characterized for individual molecular species of lecithins of rat mesenteric lymph chylomicrons and rat plasma HDL. Studies were performed in the absence of lipid transfer proteins. Donor (chylomicrons) and acceptor (HDL) particles were present in ratios of 1:1 and 1:10 with respect to total phospholipid. Biphasic exchange kinetics were observed for all major lecithins common to chylomicrons and HDL at both proportions of donor to acceptor particles. During the early rapid phase of exchange, complete in about 30 min, 40-60% of the total lecithin pool was exchanged. Initial exchange rates were most rapid for the more hydrophilic species of the major lecithins normally present in both lipoproteins. Calculated activation energies correspondingly were least for a diunsaturated lecithin (18:1-20:4), intermediate for lecithins were 16:0 in position-1 (16:0-18:2 and 16:0-20:4), and highest for analogous lecithins with 18:0 in position-1. A 10-fold increase in the ratio of acceptor to donor particles affected neither the biphasic nature of the exchange nor the rates of exchange of individual molecular species (consistent with exchange by diffusion rather than by particle collisions). Total equilibration of individual molecular lecithin species was achieved by 24 hr (37 degrees C, donor to acceptor ratio of 1:1) with only a small change in the relative mass of lecithins in chylomicrons and HDL. Novel lecithins containing 18:3, incorporated into chylomicrons, were found to exchange exceedingly rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enzyme cytochemical and immunocytochemical studies of flask cells in the amphibian epidermis

Summary The localization of oxidoreductases and transport enzymes in flask cells of the amphibian epidermis was studied at the light-microscopic level. In these cells, the deposition of cytochemical reaction products was very similar to that found in fish epidermal ionocytes, thus demonstrating histochemical similarities between these two types of cells. The present histochemical results revealed high levels of activity of alkaline phosphatase (ALPase), potassium-dependent nitrophenylphosphatase (K⁺-p-NPPase) and carbonic-anhydrase isozymes (CA-I and CA-II) in the apical region of the flask cells, indicating that enzyme zonation may be the main site of the ion pumping.     

Retention of cryptic genes in microbial populations

Cryptic genes are silenced genes that can still be reactivated by mutation. Since they can make no positive contribution to the fitness of their carriers, it is not clear why many cryptic genes in microbial populations have not degenerated into useless DNA sequences. Hall et al. (1983) have suggested that cryptic genes have persisted because of occasional strong environmental selection for reactivated genes. The present mathematical study supports their suggestion. It shows that a cryptic gene can be retained without having any selective advantage over a useless DNA sequence, if selection for the reactivated gene occasionally occurs for a substantially long time.      

Serotonin-like immunoreactive cells in the pulmonary epithelium of ancient fish species

The pulmonary mucosa of three species of ancient fish was studied immunohistochemically to show the distribution of serotonin, regarded as the main monoamine of mammalian bronchopulmonary paraneurons. Serotonin-like immunoreactive cells, dispersed through the airway epithelium as single cells, were found in all the fish species studied. They are presumably equivalent to the neuroendocrine cells reported in the lungs of mammalian and submammalian vertebrates. However, the precise role and the function of these cells remain unknown. Since the species studied belong to the most primitive extant groups of ancient fish, the present investigation suggests that serotonin is widely distributed in the lungs of the vertebrates. Several peptides, known to be specific cytochemical markers for the identification of the pulmonary neuroendocrine cells of mammals, are being investigated in the lungs of the fish species studied. They may help to trace the phylogeny of the pulmonary neuroendocrine cell system and to elucidate its function in lower vertebrates.     

Serotonin-like immunoreactivity in the epidermal club cells of teleost fishes

The present immunocytochemical study concerns the distribution of serotonin in the epidermis of three species of teleost fish. Serotonin-like immunoreactivity was found in the club cells of Heteropneustes fossilis and Carapus acus but not in those from the sea eel Conger conger. This study is the first immunocytochemical identification of serotonin in the club cells of teleost epidermis. By comparing data from the literature (Zaccone et al. 1986, 1987, 1988) regarding the occurrence of serotonin and GRP/bombesin in the exocrine sacciform gland cells of piscine skin, it is worthy mentioning here that the serotonin contained in the club cells of the species studied may have the ability to affect the pheromonal or other possible functions of these cells. The presence of serotonin in these systems has been correlated with the capacity of the exocrine glands of fish skin to secrete, ectopically, amine messengers in contrast to those produced eutopically i.e. in the neuron-paraneuron system in some vertebrates (Fujita et al. 1988).