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C Torp-Pedersen

Publications and source records attributed to C Torp-Pedersen.

101 records · Page 6Linked to original sources
PubMed1981

Effects of Ca2+ and calmodulin on cyclic nucleotide metabolism in neurosecretosomes isolated from ox neurohypophyses.

In neurosecretosomes, isolated from ox neurohypophyses, both guanylate and adenylate cyclase activity was shown to be predominantly membrane-bound. Membrane-bound adenylate cyclase was inhibited by increasing the ionized calcium concentration from 10(-7) M to 10(-5) M, but was stimulated by calmodulin in the presence of 10(-7) M and 10(-5) M ionized calcium. In contrast, neither calcium ions nor calmodulin affected the activity of membrane-bound guanylate cyclase. Soluble cyclic AMP and cyclic GMP phosphodiesterase activities increased with increasing ionized calcium concentration (10(-7) M to 10(-3) M). At 10(-7) M ionized calcium concentration, both soluble phosphodiesterase activities were stimulated by calmodulin. Both the membrane-bound phosphodiesterase activities were inhibited by a high ionized calcium concentration (10(-3) M) and not affected by calmodulin.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1980

ATP-dependent Ca2+ accumulation by microvesicles isolated from bovine neurohypophyses.

Microvesicles with and without coats were isolated from bovine neurohypophyses by a series of ultracentrifugation steps. They were similar to microvesicles previously isolated from brain. In the presence of ATP and Mg2+, the microvesicles accumulated calcium. Oxalate stimulated and the Ca2+ ionophore A23187 inhibited calcium accumulation. In the presence of Ca2+ and Mg2+ the microvesicles also demonstrated ATPase activity. As judged by SDS electrophoresis in polyacrylamide gels microvesicle protein composition was very different from that of neurosecretory granules, suggesting that they are not granule membranes "retrieved" after exocytosis. They may have an important function in regulation of Ca2+ ion concentration.

Adenosine Triphosphatases↗
PubMed1980

Isolation and characterization of secretory vesicles from bovine neurohypophyses.

A procedure is described for the isolation of secretory vesicles from bovine neurohypophyses by differential centrifugation followed by density gradient centrifugation on iso-osmolal gradients of percoll/sucrose. Only negligible contamination of the secretory vesicle fraction with markers for mitochondria, microsomes and plasma membranes could be detected. The amount of Ca2-ATPase in the isolated neurohypophysial secretory vesicles was of the same low order of magnitude as that of (Na, K)-ATPase. Thin-section electromicrographs confirmed the high purity of the isolated secretory vesicle fractions, In freeze-fracture electronmicrographs, vesicle fusion was demonstrated after incubation with Ca2. As shown in dodecyl sulfate-gel electrophoresis and subsequent autoradiography secretory vesicles exhibited an endogenous phosphorylation activity. The secretory vesicles contained an average of 23.1 microgram vasopressin/mg of protein. On incubation in media differing in ionic strength, pH and Ca2 concentration the vesicles were stable for at least 1 h.

Animals↗
PubMed1979

Studies on a Ca2+-dependent nucleoside triphosphate pyrophosphohydrolase in rat liver plasma membranes.

A membrane-bound Ca2+-dependent nucleoside triphosphate pyrophosphohydrolase was solubilized in deoxycholate, separated from inorganic pyrophosphatase, and partially characterized. The Km for a variety of substrates was determined. At 10(-4) M free Ca2+ (pH 8.0) the Km values for ATP and GTP were 0.32 and 2.2 microM, respectively. With ATP as substrate, Mg2+, Sr2+, and Ba2+ could only replace Ca2+ to a limited degree. Both purine and pyrimidine nucleoside triphosphates were hydrolyzed yielding PPi and mononucleotides and similarly AMP and formed from adenosine-(beta gamma-methylene)triphosphate. UDPglucose was hydrolyzed at the pyrophosphate bond. Tripolyphosphate and phosphoribosyl-1-pyrophosphate (P-rib-PP) were not hydrolyzed. Substrate competition experiments showed that GTP inhibited pyrophosphohydrolysis of ATP competitively. However, UDP glucase and adenosine-(beta gamma-methylene)triphosphate inhibited ATP pyrophosphohydrolysis in a non-linear manner. Adenosine-(beta gamma-methylene)triphosphate inhibited pyrophosphohydrolysis of UDPglucose non-competitively, whereas UDPglucose inhibition of adenosine-(beta gamma-methylene) triphosphate pyrophosphohydr-lysis was competitive. The molecular weight of ATP pyrophosphohydrolase was estimated at 120 000 and the pI at 5.1 Pyrophosphohydrolysis of adenosine-(beta gamma-methylene)triphosphate was studied in a number of rat organs. Nearly all activity could be sedimented at 50 000 X g. Very high activities were found in liver, kidney and small intestine, whereas low activities were found in brain and blood.

Adenosine Triphosphate↗
PubMed1979

ATP-induced release of vasopressin from isolated bovine neurohypophyseal secretory granules. Dependency on chloride and effects of analogues of ATP.

Secretory granules isolated from bovine neurohypophyses released vasopressin in the presence of a buffered medium containing ATP, Mg2+ and KCl. Substitution of K+ in the medium with Na+ or choline did not affect the release. Substitution of Cl- with either sucrose, sulphate or acetate strongly reduced the release. Analogues of ATP, substituted at the beta-gamma anhydride bond with methylene or imido groups caused a smaller release which was not related to a very small breakdown of analogues that occurred. It is suggested that at least part of the ATP induced release is due to a physicochemical action.

Adenosine Triphosphate↗
PubMed1978

A calcium ion-dependent adenosine triphosphate pyrophosphohydrolase in plasma membrane from rat liver. Demonstration that the adenosine triphosphate analogues adenosine 5'-[betagamma-imido]triphosphate and adenosine 5'-[betagamma-methylene]-triphosphate are substrates for the enzyme.

An ATP pyrophosphohydrolase in a rat liver plasma-membrane subfraction was studied with respect to specific Ca2+ activation of the beta-phosphate bond hydrolysis. ATP and, in addition, adenosine 5'-[betagamma-imido]triphosphate and adenosine 5'-[betagamma-methlylene]triphosphate were substrates for Ca2+-stimulated enzymic hydrolysis of the beta-phosphate bond. A 15-fold activation was observed by raising the free Ca2+ concentration from 10(-7) to 10(-5) M. Mg2+ had little effect. Solubilization in 1% deoxycholate and partial purification on a sucrose density gradient resulted in a 5-fold increase in specific activity with unaltered Ca2+-stimulation pattern. The possible importance of the enzyme in Ca2+ transport is discussed.

Adenosine Triphosphatases↗
PubMed1975

Effects of calcium and sodium on vasopressin release in vitro induced by a prolonged potassium stimulation.

Groups of isolated hemilobes of rat neurohypophyses were stimulated for 90 min with a 56 mM K+ concentration in the surrounding medium. The rate of release of vasopressin into the medium showed an early maximum followed by a long phase of decline which lasted for most of the stimulation period. When 3 min collection periods were employed, higher secretion rates were obtained than when using 10 min periods. This may be due to a higher rate of removal of vasopressin from the tissue and a lower vasopressin inactivation when 3 min periods are used. When Na+ was replaced by sucrose in the incubation medium for the whole stimulation period, much higher secretion rates than previously reported were obtained (13% of the total hormone content in the first 30 min period and 21% for the total 90 min period). When Na+ was removed from the incubation medium late in the stimulation period, a new high secretion rate was induced, provided that extracellular calcium was present. When Ca-2+ was removed from the medium 3 min after start of the stimulation with 56 mM K+, the secretion rate fell very rapidly. Reintroduction of a normal Ca-2+ concentration caused a new marked increase in secretion rate. These results further stress the importance of extra-cellular calcium for release of vasopressin. In addition they show that a considerable fraction of the vasopressin present in the neurohypophysis can be mobilized during a continued strong stimulation if sodium is omitted from the medium.

Animals↗