摘要:

The slowly activating potassium current, termed Iks [1], was measured in guinea pig ventricular myocytes with the whole-cell patch clamp configuration. With low concentrations of Ca2+ buffer (0.1 mM EGTA or BAPTA) in the recording pipette, a temperature increase from 21 to 31°C dramatically accelerated activation of Iks· Isoproterenol increased Iks under such conditions 2- to 3-fold at both temperatures. With high internal Ca buffer concentrations (EGTA or BAPTA ≧ 10 mM), Iks was regulated by isoproterenol at 31° C but not at 21°C. We conclude that β-receptor regulation of Iks is temperature and [Ca2+]i dependent. A mechanism consistent with the results is that Ca2+ and temperature increase the availability of subunits for channel formation and regulation by the β-adrenergic

ISSN:1094-9313    

DOI:10.1159/000154704

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

We report that Xenopus oocytes injected with wild-type cystic fibrosis transmembrane regulator (CFTR) RNA exhibit cAMP-regulated Cl– currents. Injection of CFTR RNA bearing Rl 1 7H, a mutation associated with mild disease, induces cAMP-regulated Cl– currents. The magnitudes of the currents induced by R117H were consistently lower than those induced by expression of wild-type CFTR. Western blotting with anti-CFTR antibody confirms that protein was expressed in oocytes injected with either normal or the mutant form of CFTR mRNA. The rank order of single channel open channel probabilities of wild-type and mutant CFTR Cl– R117H. These data demonstrate that mutations in the transmembrane region affect CFTR channel properties and are consistent with the hypothesis that CF disease severity may be correlated with reduced cAMP-regulated Cl– conductances of muta

ISSN:1094-9313    

DOI:10.1159/000154705

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

An electrical characterization of the isolated, perfused malpighian tubule of Formica polyctena and F. rufa is reported. Some specific problems of the perfusion method as applied to malpighian tubules of the ant are discussed and a practical solution presented. Estimates for the individual membrane resistances are derived. The shunt is investigated by basolateral biionic replacements and found to be anion specific. The Cl– pathway is further investigated by the addition of Cl– channel blockers, 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) and 4,4’-diisothiocyano-2,2’-stilbenedisulfonate (DIDS), to the lumen. The lack of effect suggests the absence of DIDS- and NPPB-sensitive Cl–

ISSN:1094-9313    

DOI:10.1159/000154706

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

Human megakaryoblastic cells (platelet precursor cells) grown in culture were sectioned for immunohistochemistry. Incubating these cells with a monoclonal antibody (JA8) directed against the human erythrocyte Ca2+ pump showed specific staining of the plasma membranes. PCR analysis of RNA from these cells demonstrated specific sequences for type HPMCA1, HPMCA2 and HPMCA4 Ca2+ pump isoforms. Western blot analysis of megakaryoblastic cells, whole platelets, and platelet membranes using monoclonal antibodies JA8, 5F10, and 3C2, directed against plasma membrane Ca2+ pump showed staining of a major band of Mr 120,000. Taken together, these studies demonstrate the existence of plasma membrane Ca2+ pump epitopes in human platelets and megakaryoblastic cells.

ISSN:1094-9313    

DOI:10.1159/000154707

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The specific activities of some glucose and glycogen degradative enzymes were studied in serially subcultured fibroblasts harvested at the same state of growth and replication. A continuous increase in the activities of phosphofmctokinase, lactate dehydrogenase, and glycogen phosphorylase was noted beyond passage 10 equalling 677 ± 74.8,170 ± 34.1, and 317 ± 57.6% of control activity at passage 25, respectively. There was a concurrent increase in the glycogen content of cells reaching a maximum of 1,498 ± 223% of control at passage 15 and maintained nearby at passages 20 and 25. Citrate synthase activity was profoundly increased at passage 15 but drastically dropped at passages 20 and 25. There were no significant variations in the above parameters between passages 1 and 10 of subculture. This enhancement of glycolytic activity which accompanies the aging (subculture) process could not be depressed as a result of improved oxygenation of the cultu

ISSN:1094-9313    

DOI:10.1159/000154708

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The effects of low-density lipoprotein (LDL) from normolipidemic (NL) and familial hypercholesterolemic (FH) human subjects on the smooth muscle cell (SMC) proliferation were examined, along with the antiproliferative actions of heparin and glycosaminoglycans (GAGs) in this system. Cell growth was stimulated from 146 to 176% by FH-over NL-LDL. This proliferative effect of FH-LDL was accompanied by an increase in the membrane cholesterol content and an increase in Ca2+ influx. These effects of FH-LDL were partially inhibited (50%) following methylation of apoprotein B100· The effects of FH-LDL were abolished by heparin and sulfated GAGs and this inhibitory effect was also accompanied by normalization of Ca2+ influx and cell membrane cholesterol. Electrokinetic analysis demonstrated a reduced net negative charge of FH-LDL relative to that of NL-LDL. We hypothesize that LDL surface charge may regulate the movement of cholesterol into the SMC plasma membrane where its presence in excess alters SMC function. Taken together, these results implicate a role for FH-LDL cholesterol as an important factor in the alteration of SMC cell growth kinetics in hypercholesterolemia, a process which can be modulated by heparin and sulfated GAGs

ISSN:1094-9313    

DOI:10.1159/000154709

出版商:S. Karger AG    

年代:1994

数据来源: Karger

ISSN:1094-9313    

DOI:10.1159/000154710

出版商:S. Karger AG    

年代:1994

数据来源: Karger