酸性水和投加铝、钙对鲢鱼早期发育和鳃超微结构的影响

在实验室条件下,研究了酸性水和投加铝、钙对鲢鱼胚胎孵化和鱼苗存活以及幼鱼鳃超微结构的影响。pH4.0引起所有胚胎在24小时内死亡,暴露于pH4.5—6.0的胚胎孵化率和暴露于pH4.0—6.0的5—15日龄鱼苗存活率随pH值上升而增高。投加0.5mg Al~(3+)/L使在酸性pH暴露条件下的胚胎孵化率和鱼苗存活率进一步降低。投加3.0mg Ca~(2+)/L可显著提高暴露于pH4.5和5.0的胚胎孵化率;投加2.0mg Ca~(2+)/L可在一定程度上提高暴露于pH4.5和5.0的鱼苗存活率。幼苗经pH4.5暴露8小时后出现严重的鳃超微结构损害;投加1.0mg Al~(3+)/L使鳃结构损害加剧;投加5.0mg Ca~(2+)/L可明显缓解酸性水对鳃的损害。     

Processing of behaviorally relevant temporal parameters of acoustic stimuli by single neurons in the superior olivary nucleus of the leopard frog

Summary Response characteristics of 130 single neurons in the superior olivary nucleus of the northern leopard frog (Rana pipiens pipiens) were examined to determine their selectivity to various behaviorally relevant temporal parameters [rise-fall time, duration, and amplitude modulation (AM) rate of acoustic signals. Response functions were constructed with respect to each of these variables. Neurons with different temporal firing patterns such as tonic, phasic or phasic-burst firing patterns, participated in time domain analysis in specific manners. Phasic neurons manifested preferences for signals with short rise-fall times, thus possessing low-pass response functions with respect to this stimulus parameter; conversely, tonic and phasic-burst units were non-selective and possessed all-pass response functions. A distinction between temporal firing patterns was also observed for duration coding. Whereas phasic units showed no change in the mean spike count with a change in stimulus duration (i.e., all-pass duration response functions), tonic and phasic-burst units gave higher mean spike counts with an increase in stimulus duration (i.e., primary-like high-pass response functions). Phasic units manifested greater response selectivity for AM rate than did tonic or phasic-burst units, and many phasic units were tuned to a narrow range of modulation rates (i.e., band-pass). The results suggest that SON neurons play an important role in the processing of complex acoustic patterns; they perform extensive computations on AM rate as well as other temporal parameters of complex sounds. Moreover, the response selectivities for rise-fall time, duration, and AM rate could often be shown to contribute to the differential responses to complex synthetic and natural sounds.Abbreviations SON superior olivary nucleus - DMN dorsal medullary nucleus - TS torus semicircularis - FTC frequency threshold curve - BF best excitatory frequency - PAM pulsatile amplitude modulation - SAM sinusoidal amplitude modulation - SQAM square-wave amplitude modulation - MTF modulation transfer function - PSTH peri-stimulus time histogram     

氟中毒抑制大鼠泌鼠的实验研究

The effect of fluorosis on lactation, lactotroph function and ultrastructure were studied in lactating rats. The results were as follows: 1) Inhibition of lactation in lactating rats with chronic fluorosis was assessed by stunting growth of pups and decrease in the amount of milk suckled by pups in 30 min. Metoclopramide, a blocker of dopamine receptor, could improve lactation in these rats. 2) During chronic fluorosis serum PRL level was decreased, however, PRL content in pituitary was increased. Electronmicroscopic examination showed accumulation of large mature secretory granules and appearance of extremely large abnormal secretory granules in lactotroph cytoplasma. These findings indicate that hormone release of pituitary lactotrophs is obstructed in lactating rats with fluorosis, and the toxic effect of fluoride is mediated by an enhanced function of dopaminergic system in hypothalamus.     

Ligand-triggered conformational perturbations elicit changes at the single cysteinyl residue of spinach calmodulin

Following application of stoichiometric amounts of Ca2+ or specific partner peptides to spinach calmodulin, dynamic changes in the nanosecond range could be monitored at a strategically anchored fluorescence or spin probe. For these studies the single cysteinyl residue 26 of spinach calmodulin was labelled with a thiol-specific proxyl (i.e. 2,2,5,5-tetramethyl-1-pyrrolidinyl-oxyl) spin probe or with a bimane fluorescence probe. With Ca2+ and a specific ligand (mastoparan) present, fluorescence studies (anisotropy, lifetime) indicated that the rotational motion of the protein complex becomes slower relative to the motion of calmodulin in the absence of the specific ligand. The probe's attachment site 26 appears to reside in a fairly polar microenvironment as reported by a series of proxyl spin probes varying in label length. The rotational correlation time of the shortest spin probe markedly changed upon binding of a specific peptide to a calmodulin region distant from that of the monitoring spin probe. We interpret these observations as indicating that ligand-triggered conformational perturbations are eliciting specific responses at the cysteinyl residue 26 of spinach calmodulin.     

Characterization of the membrane-bound protein kinase C and its substrate proteins in canine cardiac sarcolemma

Cardiac sarcolemma was purified from canine ventricles. Enrichment of the sarcolemmal membranes was demonstrated by the high (Na+ + K+)-ATPase activity of 28.0 +/- 1.5 mumol Pi/mg protein per h and the high concentration of muscarinic receptors with the Bmax of 8.2 +/- 2.5 pmol/mg protein as determined by [3H]QNB binding. The purified sarcolemma also contains significant levels of a membrane-bound Ca2+ and phospholipid-dependent protein kinase (protein kinase C). To elucidate the protein kinase C activity in sarcolemma, a prior incubation of the membranes with EGTA and Triton X-100 was necessary. The specific activity of protein kinase C was found to be 131.4 pmol Pi/mg per min, in the presence of 6.25 micrograms phosphatidylserine and 0.5 mM CaCl2. Treatment of sarcolemma with 12-O-tetradecanoylphorbol 13-acetate (TPA) and phorbol 12,13-dibutyrate (PBu2) resulted in a concentration-dependent activation of protein kinase C activity. The effect of TPA and PBu2 on protein kinase C in sarcolemma was independent of exogenous Ca2+ and phosphatidylserine. Polymyxin B inhibited phorbol-ester-induced activation of protein kinase C activity. The distribution of protein kinase C in the cytosolic fraction was also examined. The specific activity of the kinase in the cytosolic fraction was 59.7 pmol Pi/mg per min. However, the total protein kinase C activity in the cytosol was 213500 pmol Pi/min, compared to that of 1025 pmol Pi/min in the sarcolemma isolated from approx. 100 g of canine ventricular muscle. Several endogenous proteins in cardiac sarcolemma were phosphorylated in the presence of Ca2+ and phosphatidylserine. The major substrates for protein kinase C were proteins of Mr 94 000, 87 000, 78 000, 51 000, 46 000, 11 500 and 10 000. Most of these substrate proteins have not been identified before. Other proteins of Mr 38 000, 31 000 and 15 000 were markedly phosphorylated in the presence of Ca2+ only. Phosphorylation of phospholamban (Mr 27 000 and 11 000) was also stimulated in the presence of Ca2+ and phosphatidylserine, but the low Mr form of phospholamban was distinct from two other low Mr substrate proteins for protein kinase C. Polymyxin B was more selective in inhibiting the protein kinase C dependent phosphorylation. On the other hand, trifluoperazine selectively inhibited the phosphorylation of phospholamban and Mr 15 000 protein. Although the exact function of this kinase is unknown, based on these observations, we believe that protein kinase C in the cardiac sarcolemma may play an important role in the cell-surface-signal regulated cardiac function.     

Transforming growth factor beta regulates the inhibitory actions of epidermal growth factor during granulosa cell differentiation

The effects of transforming growth factor beta (TGF-beta) on epidermal growth factor (EGF) receptor content and EGF action were studied in cultured granulosa cells from immature diethylstilbestrol-implanted rats. During follicle-stimulating hormone (FSH)-induced differentiation in vitro, EGF receptors increased by 20-fold as measured by the binding of 125I-EGF to the intact cells. Addition of TGF-beta during the 48-h culture period amplified the stimulatory effects of FSH on EGF receptors up to 2-fold, with ED50 and maximal concentrations of 2.5 and 8 pM, respectively. Also TGF-beta alone in amounts from 1.6 to 16 pM increased EGF receptor content 4-fold. The stimulatory effects of TGF-beta were due to increased numbers of EGF receptors/cell, since the growth factor had no effect on the Kd (3-5 X 10(-11) M) of the high-affinity EGF binding site. TGF-beta action was observed within 20 h of granulosa cell culture and was maximal by 48 h of a 96-h culture. The stimulatory actions of TGF-beta in gonadotropin-induced cells were exerted through the cAMP effector system of the granulosa cell, since the growth factor also amplified the induction of EGF receptors by cholera toxin, forskolin, and 8-bromo-cAMP. The augmentation of EGF receptors by TGF-beta resulted in a parallel 2-fold increase in the inhibitory effects of EGF on FSH-induced cAMP production and luteinizing hormone receptor expression during granulosa cell development. TGF-beta did not increase granulosa cell numbers during culture although it elevated [3H]thymidine incorporation into DNA by 2-fold over that of FSH-treated cells. These results indicate that TGF-beta regulates the effects of both FSH and EGF during granulosa cell differentiation and provides evidence that ovarian function may be controlled by the combined actions of gonadotropins and multiple growth factors.     

Biosynthesis, glycosylation, movement through the Golgi system, and transport to lysosomes by an N-linked carbohydrate-independent mechanism of three lysosomal integral membrane proteins

The biosynthesis, glycosylation, movement through the Golgi system, transport to lysosomes, and turnover of three lysosomal integral membrane proteins (LIMPSs) have been studied in normal rat kidney cells using specific anti-LIMP monoclonal antibodies. Immunoelectron microscopy studies revealed the presence of LIMPs in secondary lysosomes, Golgi cisterna, and coated and uncoated vesicles located in the trans-Golgi cisterna, area. Pulse-chase experiments recorded LIMP precursors of 27 (LIMP I), 72 (LIMP II), and 86 kDa (LIMP III) and mature LIMPs of 35-50 (LIMP I), 74 (LIMP II), and 90-100 kDa (LIMP III). Time course studies on the acquisition of endoglycosidase H resistance by LIMPs indicated that all three LIMPs moved from the site of their synthesis in the endoplasmic reticulum to the medial Golgi within 30-60 min after their synthesis. All three LIMPs were fully glycosylated before leaving the Golgi system, the process during which LIMP I was retained in the trans side of the organelle. LIMP I reached the lysosomes with a halftime of 2 h and LIMPs II and III with half-times of 1 h after their synthesis by a mechanism that was independent of N-linked carbohydrates. LIMPs free of N-linked carbohydrates displayed much shorter half-lives than fully glycosylated LIMPs, suggesting an important role of the sugars in protecting LIMPs against proteolytic degradation. Double immunofluorescence microscopy experiments showed that LIMP I, LIMP II, and LIMP III are localized in the same lysosomes.