The role of calcium and potassium ions in the response of the mouse mammary secretory and myoepithelial cells to treatment with oxytocin

Experiments were carried out in lactating white mice. Removal of Ca(2+)-ions from the perfusion solution reduced the amplitude and duration of the membrane potential changes in the secretory cells in the mammary gland alveolus. The extra- and intracellular Ca(2+)-ions participate in development of contraction responses of myoepithelial cells. Removal of K(+)-ions from perfusion solution and increase of K(+)-ions concentration in the medium to 20 mmol/l inhibit the development of response of secretory cells to oxytocin action. These changes in K(+)-ions concentration do not affect the contractile response of the myoepithelial cells. The findings suggest that there are essential differences in the participation of Ca(2+)- and K(+)-ions in mechanisms of the mammary secretory and myoepithelial cells responses to oxytocin action.     

Localization of plasma membrane and secretory calcium pumps in the mammary gland

Until recently the mechanism for the enrichment of milk with calcium was thought to be almost entirely via the secretory pathway. However, recent studies suggest that a plasma membrane calcium ATPase, PMCA2, is the primary mechanism for calcium transport into milk, highlighting a major role for apical calcium transport. We compared the expression of the recently identified secretory calcium ATPase, SPCA2, and SPCA1, in the mouse mammary gland during development. SPCA2 levels increased over 35-fold during lactation with expression localized to luminal secretory cells, while SPCA1 increased only a modest 2-fold and was expressed throughout the cells of the mammary gland. We also observed major differences in the localization of PMCA2 and PMCA1. Our studies highlight the likely specific roles of PMCA2 and SPCA2 in lactation and indicate that calcium transport into milk is a complex interplay between apical and secretory pathways.     

Changes in mammary secretory epithelial reactions to oxytocin action under the influence of ouabain

Changes in shape and volume of mammary secretory cells and in their RNA content, under the action of oxytocin, are considered. Under ouabain suppression of Na,K-ATPase activity, no swelling or shape changes occur in the secretory cells, in addition to no increase in their RNA content, which is characteristic of the cell reaction during the initial period of oxytocin action.     

Localization of acid phosphatase in lactating rat mammary glands

Summary Localization of acid phosphatase in mammary glands of lactating rats was studied by both biochemical and cytochemical methods. Cytochemically, acid phosphatase activity was detected by using lead citrate as the capture agent for the inorganic phosphate released from p-nitrophenyl phosphate. The activity was predominantly localized in the lumina of the endomembrane system and in the milk that had been secreted into the alveolar lumen. Biochemically, acid phosphatase was present in all the subcellular fractions with higher activities in the membrane-associated fractions. The localization of tartrate-resistant acid phosphatases within the endomembrane system of fully lactating rat mammary tissue suggests a possible role for these enzymes in milk secretory processes.Abbreviations ASMX 3-hydroxy-2-naphthoic acid 2,4-dimethylanilide - DMSO dimethylsulfoxide - DTT dithiothreitol - EDTA ethylenedinitrilo tetra-acetic acid - FGM fat globule membranes - MES 2-(N-morpholino) ethanesulfonic acid - PCMB p-chloromercuribenzoate - p-NPP p-nitrophenyl phosphate     

Physiology of secretory cells in the mouse mammary gland

Secretory cells' membrane potential and transepithelial potential difference in the mouse mammary gland diminish within 2.5 hours following breast-feeding of the litter. The transepithelial resistance for up to 20 hours after the feeding did not drop below 40-70 k omega. The secret pressure in the mammary gland does not grow during this period. Therefore an increase of interval between litter feeding up to 20 hours does not entail any mechanical lesion of the secretory epithelium. The latter's cells seem to secrete organic and inorganic substances in concentrations which do not change significantly during their transfer along the outgoing ducts.     

Endocytic prolactin routes to the secretory pathway in lactating mammary epithelial cells

Plasma-borne prolactin is carried from blood to milk by transcytosis across the mammary epithelial cell through the endocytic and secretory pathways. To determine the precise route of prolactin endocytosis, intracellular transport of biotinylated prolactin was monitored, in parallel with endocytosis of fluorescein isothiocyanate-conjugated dextran and IgG, by using pulse-chase experiments in lactating mammary fragments and in enzymatically dissociated acini. Biotinylated prolactin was sorted to vesiculo-tubular organelles whereas dextran was very rapidly carried to the lumen and IgG remained accumulated in the basal region of cells. To determine whether prolactin uses routes into and across the Golgi and trans-Golgi network, localisation of biotinylated prolactin was combined with the immunofluorescence detection of caseins and, respectively, p58 and TGN38. Biotinylated prolactin strongly colocalised with caseins during a chase but not all or only very little with p58 and TGN38. To characterise the organelles involved in transcytosis, gold-labelled prolactin, experimentally accumulated in late endosomes and which recovered a normal transport, was localised by electron microscopy. In mammary fragments incubated at low temperature, and in mammary fragments from rats fed with a lipid-deprived diet, transport of gold-labelled prolactin was restored by increasing the temperature and by adding arachidonic acid, respectively. These data demonstrate that a sorting occurs very rapidly between prolactin, dextran and IgG. They suggest that prolactin may reach the biosynthetic pathway after direct fusion between multivesicular bodies and secretory vesicles.     

Preservation of the secretory response of peritoneal mast cells in the absence of extracellular calcium

The transfer of rat peritoneal mast cells from balanced salt solution to calcium-free buffer led to a time-dependent decrease in their response to compound 48/80 and to ionophore A23187. The concomittant absence of potassium from the calcium-free buffer enabled the mast cells to retain their secretory response. The increase in potassium level, with a parallel decrease in sodium to maintain osmolarity, led to a slight potentiation of the response to 48/80 and to a large but transient potentiation of the response to A23187. Mast cells can be considered nonexcitable. The apparent dependency upon extracellular calcium of mast cell secretory responses might be related to the presumed tight equilibrium between endoplasmic reticulum calcium stores and extracellular calcium. The control of this equilibrium by transmembrane gradients of monovalent ions is proposed.     

Ultrastructural analysis of the role of microtubules in the transport and exocytosis of protein secretion in secretory cells of mouse mammary glands

Morphometrical analysis of microtubules (MT) and coated vesicles (CV) was done on electron micrographs of the murine mammary gland sections at the final stages of functional maturation of secretory cells (SC), as well as at different stages of the cell secretory cycle (CSC). The results obtained allow to make the following conclusions: 1) dynamics of changes in the MT count in different subplasmalemmal cell compartments is similar, being directly associated with heterochronical character of CSC processes; 2) the maximum MT count in SC was seen during formation of the secretion product, this increase occurring at the expense of short MT, which are disassembled before and during exocytosis of secretory vesicle (SV) contents; 3) changes in the number of MT and CV are of similar character, which was revealed by morphometrical analysis of SC in the course of maturation. The number of MT and CV in SC increased rapidly and significantly on the 1st and 2nd days after parturition, compared to that observed 1-2 days before parturition. However, the number of MT and CV decreased by the 10th day of lactation, when the mammary secretory activity reached its maximum. Both correlation and regression statistical analyses made during the CSC development point to a linear relation between MT (x) and CV (y) numbers. Regression of y on x is: y = -0.89 + 12.43x. A hypothesis about the possibility of MT participation in CV and SV transport and in the formation of a barrier on the path leading to exocytosis of SV contents is suggested.     

Histochemical characteristics of the secretory cells of gastric glands compared

The work is dedicated to complex histological studies of the secreting cells in the gastric fundal glands, in their comparative aspect. In the representatives of Amphibia, Reptilians and birds, histochemical differentiation of oxyntopeptic cells was demonstrated to be independent on the peculiarities of the animal nutrition. In mammals, histochemical characteristic of the carbohydrate component in the glandular secreting cells depends on the type of nutrition.     

Effects of pilocarpine on the secretory acinar cells in human submandibular glands

Pilocarpine has been used as a choice of drugs for treatment of impaired salivary flow. Although considerable data are available as to the stimulatory effect of pilocarpine on the salivary secretion in human, its underlying mechanism, at the cellular level, has not been rigorously studied. In this experiment, we studied the effect of pilocarpine on the ion channel activity, cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) and aquaporin (AQP)-5 expression, which play key roles in the secretary process and determine the capacity of fluid secretion. In human submandibular gland (SMG) acinar cells, 10(-5) M pilocarpine activated the outward rectifying-current, which was predominantly K(+) selective in the whole cell patch clamp study. The pilocarpine increased [Ca(2+)](i) in a concentration-dependent manner in the range of 10(-6) M to 10(-4) M. We found that both increases of [Ca(2+)](i) and outward rectifying- K(+) current were inhibited by 10(-5) M U-73122, a specific phospholipase C inhibitor. The magnitudes of pilocarpine-induced [Ca(2+)](i) transients were approximately 55% lower than those with the same concentration of carbachol (CCh). Pilocarpine also increased the amount of AQP-5 protein in the apical membrane (APM) in human SMG acinar cells. Our results suggest that pilocarpine induce salivary secretions in human by activating K(+) channels, increasing [Ca(2+)](i) via phospholipase C dependent pathway, and increasing AQP-5 protein expression in the APM of SMG acinar cells.     

The structural organization of the cytoskeleton of the mammary secretory cells

A study was made of the arrangement and specialties of distribution in the mammary secretory cells of albino mice of the following cytoskeleton ultrastructures: microtubules (MT), organization centres (MTOC), microfilaments (MF) and intermediate filaments (IF). During the last period of pregnancy and at different stages of lactation, for the alveolar epithelium the presence of a single material centrioles (CN) was shown in the region of the apical surface near dense intercellular contact. During pregnancy and especially at the beginning of lactation (1-2 days) the relatively large density of the MT was observed in both the cytoplasm of the secretory cells and the region near the CN. On the most hard days of lactation (10 day) the lowering of the number of all the observed structures was held in the majority of the cells. The MT was not observed near the CN. It appeared that the elimination of the MTOC activity during the most hard time of lactation is related to the decrease in the numbers of MT, MF and IF. The pattern of cytoskeleton reorganization, associated with the development of the functional activity of the observed cells, enables us to suggest a cooperative contribution of its base components in the formation of the secretory surface and in the carrying out of exocytosis.     

Localization of vimentin in myoepithelial cells of the rat mammary gland

Summary Myoepithelial cells in the virgin rat mammary gland have been shown to contain vimentin, using a polyclonal antiserum to vimentin purified from hamster fibroblasts. This antiserum has been shown to be specific for vimentin by immunoblotting and ELISA techniques. Similar results were obtained with a monoclonal antibody to vimentin. In the mammary glands of pregnant rats, the staining with vimentin antibodies is much weaker in the myoepithelial cells of the developing alveolar buds than in the main ducts. Similarly, in lactating glands, the staining of myoepithelial cells is much weaker in the secretory alveoli than in lactiferous sinuses. In each case, staining with antivimentin co-localizes with staining with polyclonal antisera to callous keratin (which specifically stain myoepithelial cells in the rat mammary gland).     

Ultrastructure of the secretory cells of the submucosal glands in the human maxillary sinus

Tissue samples obtained from the lateral wall of the maxillary sinuses of five patients were examined by light microscopical, histochemical, and ultrastructural techniques. Submucosal glands were tubulo-alveolar mixed glands. The acini consisted of either all serous or all mucous cells, or a mixture of both. Serous granules were stained by toluidine blue, or by hematoxylin and eosin (H and E), but showed little or no reaction with periodic acid-Schiff (PAS) or Alcian blue. Mucous granules were pale in toluidine blue or H and E preparations, and consisted primarily of acid mucosubstances, as demonstrated by their staining reaction with PAS and Alcian blue. At the electron microscope level, the serous granules were either homogeneously dense, or showed a substructure consisting of at least two layers of distinctly different electron-opacity. Typical mucous droplets consisted of a fibrillar network dispersed in a translucent matrix. A second secretory product was present in the mucous cells in the form of elongated, membrane-bounded structures containing numerous parallel filaments, which measured about 55 Å in diameter. The mucous droplets and the filamentous bodies appear to arise from the opposite faces of the Golgi complex in the mucous cells. The filamentous bodies showed a pronounced tendency to fuse with the mucous droplets. All acini were surrounded by a well-defined myoepithelial layer and contained intercellular nerve terminals.     

Calcitonin gene-related peptide-like immunoreactive cells in the secretory portions of rat sweat glands

Summary We found cells with calcitonin gene-related peptide-like immunoreactivity and with many cored vesicles in the secretory portions of sweat glands of rat foot pads. About 10% of sweat glands contained single immunoreactive cells. The immunoreactive cells were flaskshaped, with a narrow apex facing the glandular lumen and the bulk of the cell body in the basal half of the glandular wall. In the cytoplasm, there were many vesicles, 100–250 nm in diameter, with cores of various electron densities. These cytochemical and cytological characteristics suggest that the immunoreactive cells are homologous to gastrointestinal basal granulated cells.     

Mitochondrial calcium in the life and death of exocrine secretory cells

The remarkable recent discoveries of the proteins mediating mitochondrial Ca(2+) transport (reviewed in this issue) provide an exciting opportunity to utilise this new knowledge to improve our fundamental understanding of relationships between Ca(2+) signalling and bioenergetics and, importantly, to improve the understanding of diseases in which Ca(2+) toxicity and mitochondrial malfunction play a crucial role. Ca(2+) is an important activator of exocrine secretion, a regulator of the bioenergetics of exocrine cells and a contributor to exocrine cell damage. Exocrine secretory cells, exocrine tissues and diseases affecting exocrine glands (like Sj?gren's syndrome and acute pancreatitis) will, therefore, provide worthy research areas for the application of this new knowledge of the Ca(2+) transport mechanisms in mitochondria.     

Xanthine oxidase,an indicator of secretory differentiation in mammary cells

Elevated levels of xanthine oxidase were found in (1) lactating mouse mammary glands, compared with virgin and midpregnant glands; and (2) primary mouse mammary cells cultured on floating collagen gels, compared with non-secretory cells on attached gels. In primary culture, increase in xanthine oxidase activity above a basal level coincided with secretory activity as measured by casein production; intracellular levels of casein and xanthine oxidase showed a high degree of correspondence. It is suggested that xanthine oxidase levels can be used as an indicator of in vivo and in vitro secretory differentiation in mammary epithelial cells.