Connexins 26, 32 and 43 are expressed in virgin, pregnant and lactating mammary glands

Gap junctions (GJ) are formed by a number of homologous proteins termed connexins. Here expression of connexins Cx26, Cx32 and Cx43, was evaluated by immunofluorescence (IF) in mammary glands from virgin, pregnant and lactating rats. Cx26, Cx32 and Cx43 labeling was detected in epithelial parenchymal cells at all functional stages. Cx26 and Cx32 labeling was very low in glands from virgin animals, somewhat greater in glands from pregnant animals and significantly higher (in number and size) in lactating animals. In the last ones, Cx26 and Cx32 punctate labeling was localized to the basal and lateral membranes of alveolar epithelial cells and collecting ductules. Cx43 punctate labeling was restricted to the periphery of alveoli towards the basal pole of epithelial cells at all functional stages, and it enlarged slightly during lactation. At this localization, Cx43 may form GJ between myoepithelial cells and/or between epithelial and myoepithelial cells. Cx43 was also found to be steadily expressed in the connective tissue which surrounds and invades each parenchymal lobe, at all functional stages. At this localization, Cx43 may couple fibroblasts and/or adipose cells. IF studies in sections from lactating mice showed the same distribution of connexins. Immunoblots confirmed specificity of labeling and the presence of Cx32 and Cx43 in the mammary gland. The increase in connexin expression detected during pregnancy and lactation may be important for epithelial cell differentiation and secretion in the mammary gland.     

A surface-dependent gastric evacuation model for fish

A gastric evacuation curve expresses how fast prey disappear from the stomach, and empirical models are used generally for the relationship between weight of prey remaining ( W_t ) and time ( t ) after a meal. Unfortunately, empirical models are likely to have restricted applicability because their parameters often represent limited biological mechanisms. This paper develops a simple digestion model. The simplest form of the model has four parameters; the digestion velocity (expressing enzymatic breakdown of prey), prey length, initial prey radius and the density of the prey. Two more parameters are included in an extended version; a time-delay before digestion starts and environmental temperature. The approach is based on the assumption that prey digestion is a surface process in that digestive enzymes attack progressively deeper into a prey of known size and shape so that the average digestion rate is proportional to the prey radius r (m). This process is characterized by the digestion velocity d_s (m s ^–1). Unknown parameters are estimated with uncertainty using the maximum likelihood technique. Model evaluation using published data sets demonstrated that the new model is flexible. Prey geometry is incorporated into the model and temperature effects upon gastric evacuation are linked directly to the digestion velocity.     

Secretion of HCO 3 − /OH− in cortical distal tubule of the rat

Secretion of bicarbonate has been described for distal nephron epithelium and attributed to apical Cl^–/HCO ₃ ^– exchange in beta-intercalated cells. We investigated the presence of this mechanism in cortical distal tubules by perfusing these segments with acid (pH 6) 10 mm phosphate Ringer. The kinetics of luminal alkalinization was studied in stationary microperfusion experiments by double-barreled pH (ion-exchange resin)/1 m KCl reference microelectrodes. Luminal alkalinization may be due to influx (into the lumen) of HCO ₃ ^– or OH^–, or efflux of H⁺. The magnitude of the Cl^–/ HCO ₃ ^– exchange component was measured by perfusing the lumen with solutions with or without chloride, which was substituted by gluconate. This component was not different from zero in control and alkalotic (chronic plus acute) Wistar rats. Homozygous Brattleboro rats (BRB), genetically devoid of antidiuretic hormone, were used since this hormone has been shown to stimulate H⁺ secretion, which could mask bicarbonate secretion. In these rats, no evidence for Cl^–/HCO ₃ ^– exchange was found in control BRB and in early distal segments of alkalotic animals, but in late distal tubule a significant component of 0.14±0.033 nmol/cm² · sec was observed, which, however, is small when compared to the reabsorptive flow found in control Wistar rats, of 0.95±0.10 nmol/cm² · sec. In addition, 5×10^–4 m SITS had no effect on distal bicarbonate reabsorption in controls as well as on secretion in alkalotic Wistar and Brattleboro rats, which is compatible with the absence of effect of this drug on the apical Cl^–/HCO ₃ ^– exchange in other tissues. It is concluded that most distal alkalinization is not Cl^– dependent, and that Cl^–/HCO ₃ ^– exchange may be found in cortical distal tubule, but its magnitude is, even in alkalosis, markedly smaller than the reabsorptive flux, which predominates in the rats studied in this paper, keeping luminal pH lower than that of blood.     

大肠杆菌的蛋白分泌机制

大肠杆菌的分泌蛋白定位于内膜、外膜、周质空间和胞外环境,它们在N端或C端带有一定的结构包含着分泌信号,这两类分泌蛋白在各自特定的一组蛋白因子的协助下跨越内膜,再通过目前尚不清楚的方式实现其最终定位.N端带有信号肽的分子在跨越内膜时得到Sec家族蛋白因子协助,信号肽在跨膜过程中可能被切除,该过程由ATP和电化学势提供能量.C端带分泌信号的分子主要受到Hly家族分子协助,一次穿过内膜和外膜而不经过周质空间.     

毛喉萜抑制人胃癌细胞BGC－823增殖与ras基因表达相关性研究

毛喉萜（ｆｏｒｓｋｏｌｉｎ）对人胄癌细胞ＢＧＣ－８２３增殖有明显抑制作用,具药物剂量和作用时间之依赖性。剂量为２×１０~（－５）ｍｏｌ／Ｌ之毛喉萜使胃癌细胞在软琼脂中形成集落的能力显著降低;癌基因ｃ－Ｈａ－ｒａｓ之表达明显被抑制,细胞核中与ｒａｓ基因上游调控区２．５ｋｂ片段结合的三种蛋白结合能力下降。联系到以同样浓度药物处理胃癌细胞７２ｈ,细胞质、膜与细胞核中蛋白激酶Ｃ（ＰＫＣ）活性均下降的现象,可能ＰＫＣ活性下降与Ｈａ－ｒａｓ基因上游片段２．５ｋｂ结合蛋白之结合能力下降存在相关性,ＰＫＣ可能通过影响ＤＮＡ结合蛋白的磷酸化作用,导致了Ｈａ－ｒａｓ基因表达之被阻抑。而ｒａｓ基因表达下降可能是毛喉萜抑制胃癌细胞增殖的一个重要分子事件。     

Sulfate restriction induces hyposecretion of the adhesion proteoglycan and cell hypomotility associated with increased 35SO42− uptake and expression of a band 3 like protein in the marine sponge,Microciona prolifera

Sulfate is an important component relating to normal proteoglycan secretion and normal motility in the marine sponge, Microciona prolifera. The following alterations were observed in sponge cells when sulfate free artificial sea water was used as the suspension medium: (1) impairment of aggregation, (2) loss of cell movements, (3) a marked reduction in the secretion of the adhesion proteoglycan (AP). Reversal of this effect occurred if sulfate depleted cells were again rotated in sulfate containing artificial sea water. Motility and reaggregation of sulfate deprived cells could be completely restored by purified AP, but only if cells were first pre-conditioned in normal sea water. Comparisons of ³⁵SO₄^2? uptake between normal and sulfate deprived cells which had been treated to reduce preformed secretions showed a marked increase in ³⁵SO₄^2? uptake and incorporation which could be greatly augmented in the presence of Ca²⁺/Mg²⁺. Excessive retention of AP in sulfate starved cells demonstrated by immunostaining suggested that AP secretion and cellular motility may be controlled by a sulfate dependent secretogogue or that undersulfated AP itself had developed a secretory defect. SDS-PAGE of Triton treated cellular extracts demonstrated a 116 kDa ³⁵SO₄^2? sulfated band which co-migrated with AP, but only in extracts derived from sulfate starved cells. Western blots prepared from such extracts incubated in the presence of a monoclonal anti-band 3 antibody demonstrated labelling of a single 97 kDa band only in material from sulfate deprived cells. The absence of this component in normal cell extracts indicated that this protein may be involved in facilitated sulfate transport. This study lends support to a heretofore unrecognized role for sulfate in cell motility and secretion.     

Long-term antidiabetic activity of vanadyl after treatment withdrawal: Restoration of insulin secretion?

In its vanadate (V⁵⁺) or vanadyl (V⁴⁺) forms, vanadium has been demonstrated to possess antidiabetic activity. Oral treatment of streptozotocin (STZ)-diabetic animals with either form is associated with correction of hyperglycemia, and prevention of diabetes-induced complications, although weight gain is unaffected. Vanadium treatment of non-diabetic animals lowers plasma insulin levels by reducing insulin demand, as these animals remain normoglycemic. These results suggest that vanadium hasin vivo insulin-mimetic or insulin-enhancing effects, in agreement with severalin vitro observations.Chronic treatment with vanadium has also been shown to result in sustained antidiabetic effects in STZ-diabetic animals long after treatment has ceased. Thus, at 13 weeks after withdrawal from treatment, corrected animals had normalized glucose and weight gain, and improved basal insulin levels. In addition, near-normal glucose tolerance was found despite an insignificant insulin response. Since vanadium accumulates in several tissue sites (e.g. bone, kidney) when pharmacological doses are administered, it is possible that stored vanadium may be important in maintaining near-normal glucose tolerance at least in the short-term following withdrawal from treatment. Recently, following withdrawal of vanadyl treatment up to 30 weeks, diabetic animals which had remained normoglycemic and had normalized glucose tolerance showed improvements in plasma insulin levels both in the basal state and in response to oral glucose, as compared to those which had reverted to hyperglycemia. The observed significant improvements in insulin capacity over the long-term (>3 months) suggests that a restored and/or preserved insulin secretion may be essential for maintained reversal of the diabetic state over a prolonged period after treatment is withdrawn.     

Protein tyrosine phosphorylation in cardiovascular system

Treatment of rat parotid acinar cells with sodium orthovanadate (an inhibitor of protein tyrosine phosphatase) caused a dose-dependent inhibition of phosphatase activity as measured by the hydrolysis of para nitrophenylphosphate (pNPP). Inclusion of 50 M sodium orthovanadate inin vitro gland cultures prevented the amylase secretion from both untreated control and isoproterenol-stimulated parotid acinar cells. Four different tyrosine-phosphorylated proteins with M_r 40, 45, 70 and 95 kDa, respectively, were identified in secretory granule preparations from rat parotid glands by immunoblot using a monospecific antibody for phosphotyrosine. An increase in the phosphorylation levels of these phosphoproteins was noted in the presence of 50 M sodium orthovanadate, suggesting that a protein tyrosine phosphatase (PTPase) is involved in parotid gland protein dephosphorylation reactions. Using antibody to Syp (a PTPase belonging to class 1D), a major fraction of subcellular activity was found to be associated with secretory granule membranes. These results suggest the possible involvement of a PTPase (Syp) in parotid gland secretory mechanisms.