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661.
Beta-adrenoceptor agonist isoproterenol potentiates the damaging effect of angiotensin II on rabbit aorta endothelium. Compared to the action of angiotensin II alone the amounts of injured cells, damaged intercellular contacts, cell form change, silver uptake and 125I--LDL uptake are increased under simultaneous action of angiotensin II and isoproterenol. Disturbance in barrier function is associated with the damaged cell contracts and cell death. 125I--LDL uptake increase is due to their accumulation in the adventitia. The simultaneous increase in angiotensin II and beta-adrenoceptor activating agents concentrations can damage endothelium and disturb its barrier function.  相似文献   
662.
The electrical activity of endocrine pituitary cells is mediated by a plethora of ionic currents and establishing the role of a single channel type is difficult. Experimental observations have shown however that fast-activating voltage- and calcium-dependent potassium (BK) current tends to promote bursting in pituitary cells. This burst promoting effect requires fast activation of the BK current, otherwise it is inhibitory to bursting. In this work, we analyze a pituitary cell model in order to answer the question of why the BK activation must be fast to promote bursting. We also examine how the interplay between the activation rate and conductance of the BK current shapes the bursting activity. We use the multiple timescale structure of the model to our advantage and employ geometric singular perturbation theory to demonstrate the origin of the bursting behaviour. In particular, we show that the bursting can arise from either canard dynamics or slow passage through a dynamic Hopf bifurcation. We then compare our theoretical predictions with experimental data using the dynamic clamp technique and find that the data is consistent with a burst mechanism due to a slow passage through a Hopf.  相似文献   
663.
Journal of Applied Phycology - The red alga Kappaphycus striatus “sacol” brown strain is an economically important species and extensively cultivated at Vanphong Bay, Vietnam. To...  相似文献   
664.
665.
In the accompanying work we demonstrated that the decline in expression of steroid 17 alpha-hydroxylase in mass cultures and clones of adrenocortical cells is the result of a stochastic switching process which yields mixtures of expressing and nonexpressing cells. There is an apparent positive correlation between the replicative potential of adrenocortical cell cultures and the number of cells in the culture that can express 17 alpha-hydroxylase. We investigated this by extending the cells' replicative potential by transfecting them with cloned SV40 virus. Cells from a senescent subclone, with very limited remaining replicative potential, were transfected. The cell population showed a progressive increase in growth rate and gave rise to a line of cells that expressed T antigen and which was apparently immortalized. Induction of mRNA for 17 alpha-hydroxylase by cyclic AMP was absent in this line of cells, as it was in the senescent cells prior to transfection. The cells remained responsive to gene induction by cyclic AMP as evidenced by increases in mRNA and activity for cholesterol side-chain cleavage. The absence of 17 alpha-hydroxylase expression in this line was not the result of interference by SV40 T antigen. When early passage cells were transfected with pSV3neo, which contains the early region of SV40 and neo, and were selected with G418, SV40 T antigen-expressing lines were derived which showed high levels of expression of 17 alpha-hydroxylase after induction with cyclic AMP. These cells maintained high levels of expression of 17 alpha-hydroxylase through four successive recloning events, over a period of replication much longer than that achievable by nontransfected cells. Thus, transfection by SV40 can be used to dissociate effects of senescence on growth and differentiated gene expression. T antigen expression selectively affects growth, but preserves the state of expression of a differentiated function gene as it was prior to transfection.  相似文献   
666.
At early times (1 and 24 h) following local single exposure of rabbit hindlimbs to 0.21 C/kg X-radiation Ca ATPase was isolated from sarcoplasmic reticulum of skeletal muscles and inserted in liposomes the treatment of which with trypsin resulted in the formation of proteoliposomes with a Ca ATPase hydrophobic fragment (Mr 45-50 kDa). It was shown that X-radiation increased the permeability of univalent and bivalent cations through a channel formed by the hydrophobic fragment of Ca ATPase and diminished ion selectivity of this channel.  相似文献   
667.
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