PubMed Health⌕ Search

Biomedical subjects

M E Carsten

Publications and source records attributed to M E Carsten.

At least 19 recordsLinked to original sources
PubMed1987

The binding of Ca2+ to Ca2+-transporting microsomes derived from bovine uterine sarcoplasmic reticulum.

An obligatory early step in the transport of calcium across the internal membranes of smooth muscle cells is the binding of calcium to the Ca,Mg-ATPase. The characterization of calcium binding to sarcoplasmic reticulum from smooth muscle has not been reported. Calcium binding to a bovine myometrium preparation was investigated using Scatchard analysis and a computer program utilizing weighted least squares curve fitting and an exact mathematical model of binding. This permitted objective measurement of goodness of fit and showed that best fit was obtained using a two site model. Magnesium did not change the affinity for calcium of the two sites; but reduced the number of low affinity sites to half.

Animals↗
PubMed1987

A new look at uterine muscle contraction.

Recent progress in our understanding of uterine smooth muscle contraction is reviewed. We no longer believe that actin-myosin interaction in the myometrium occurs through activation of the thin filament; but it is triggered by calcium-dependent phosphorylation of myosin in the thick filament. Calcium is now thought to originate from both extracellular and intracellular sources. Calcium can enter the cell through either a voltage- or a hormone-controlled calcium channel. The intracellular source of calcium is the sarcoplasmic reticulum. The effect of oxytocin in human labor is no longer considered the result of increased circulating oxytocin but rather of increased oxytocin receptors. In contrast, the contractile action of some prostaglandins is related to increased prostaglandin formation at human parturition. The step between hormone binding and cellular action is mediated by second messengers. The uterine-relaxing action of cyclic adenosine monophosphate is now thought to be limited to the inhibition of myosin phosphorylation. Recently discovered second messengers for contraction of the myometrium are phosphoinositides; their turnover causes calcium release from the sarcoplasmic reticulum. Guanine nucleotides are thought to be modulators of these two second messengers.

Adenosine Triphosphatases↗
PubMed1985

Ca2+ release by inositol trisphosphate from Ca2+-transporting microsomes derived from uterine sarcoplasmic reticulum.

Microsomes derived from pregnant uterine sarcoplasmic reticulum, isolated by differential and sucrose density gradient centrifugation, accumulates Ca2+ in the presence of ATP. Inositol trisphosphate caused release of this Ca2+, in a dose dependent manner. 40% of the Ca2+ that can be released by the ionophore A23187 was released by 5 microM inositol trisphosphate. Removal of Mg by EDTA prior to addition of inositol trisphosphate did not change the course of Ca2+ release. These results indicate that by mobilizing intracellular Ca2+, inositol trisphosphate may be the link between hormonal stimuli and smooth muscle contraction.

Animals↗
PubMed1984

Properties of a phosphorylated intermediate of the Ca,Mg-activated ATPase of microsomal vesicles from uterine smooth muscle.

A phosphorylated intermediate of the CaMg-ATPase is demonstrated in microsomal preparations from uterine smooth muscle. Characterization included the use of activators, inhibitors, and sodium dodecyl sulfate (SDS)-gel electrophoresis. The phosphorylation was a function of the ATP and Ca concentrations. The dissociation constant KATP was 2.7 X 10(-6) M and KCa was 1.7 X 10(-6) M. Mg was obligatory for the reaction. Na azide, ouabain, or the substitution of NaCl for KCl did not affect the reaction. Phosphorylation was inhibited by Salyrgan, ADP, or 20 mM calcium. SDS-polyacrylamide gel electrophoresis at pH 2.4 demonstrated phosphorylation of predominantly one protein with a molecular weight of 100,000. Hydroxylamine and, to a lesser extent, neutral and alkaline pH caused dephosphorylation. This indicates the presence of an acylphosphate bond in the phosphoprotein. The above findings are consistent with the phosphorylated intermediate being a Ca,Mg-ATPase. The inhibition by 20 mM calcium indicates that the Ca,Mg-ATPase of smooth muscle differs from that of striated muscle sarcoplasmic reticulum.

Animals↗
PubMed1984

Calcium-loaded microsomes from uterine smooth muscle. A biological system to test for calcium ionophore action of prostaglandins.

Smooth muscle microsomal vesicles were loaded with calcium in the presence of oxalate and ATP. The intact vesicles that contained calcium oxalate crystals were separated by ultracentrifugation from empty vesicles. This results in a unique model system, composed of a biologically active membrane with virtually all of the calcium inside. Intravesicular calcium is differentiated from externally bound calcium using ionophore X537A and EGTA. EGTA released calcium slowly with a half time of 93 min. The ionophore X537A rapidly released calcium with a half time of 12 min. This model can be used to test for calcium ionophoretic action. Prostaglandin (PG) E2 and prostacyclin (PGI2) were tested in this system. We found that PGE2 and PGI2 did not change calcium permeability.

Calcium↗
PubMed1979

Calcium accumulation by human uterine microsomal preparations: Effects of progesterone and oxytocin.

A microsomal fraction was prepared from human pregnant uteri at term and at 6 to 19 weeks' gestation, and from nonpregnant uteri by differential centrifugation and purified on a discontinuous sucrose density gradient. This fraction bound calcium in the presence of adenosine triphosphate (ATP). ATP-dependent calcium binding in microsomal preparations was found to increase with advancing pregnancy. Addition of progesterone increased the ATP-dependent calcium binding, while addition of oxytocin decreased the ATP-dependent calcium binding. In combination, oxytocin and progesterone counteracted each other. The progesterone effect was specific for progesterone; three biologically inactive analogues had no effects on calcium binding. The actions of progesterone and of oxytocin on ATP-dependent calcium binding were found to be consistent with their respective in vivo uterine relaxing and contracting actions.

Adenosine Triphosphate↗
PubMed1977

Effects of prostaglandins and oxytocin on calcium release from a uterine microsomal fraction.

A microsomal fraction resembling striated muscle sarcoplasmic reticulum was isolated from uterine smooth muscle. ATP induces calcium accumulation in this fraction. Increased temperature enhances calcium accumulation and calcium-activated ATPase. In the absence of ATP, approximately 35% of the intrinsic calcium exchanges with the 45Ca in the incubation medium. In the presence of ATP, exchange of intrinsic calcium with 45Ca increases by an amount which equals the ATP-dependent calcium binding. In preparations partially preloaded with calcium, a steady state of bound calcium is reached when the ATP is exhausted. Calcium is released under these conditions by prostaglandins E2 and F2alpha, but not by PGF1beta. The antibiotic ionophores X537A and A23187, as well as oxytocin, also release calcium previously accumulated under ATP stimulation. None of these agents, with the exception of oxytocin, release intrinsic calcium. Thus, the effect of prostaglandins resembles that of the ionophores, suggesting an ionophoretic action of these prostaglandins. The release of calcium conforms with the in vivo smooth muscle contracting action of these agents.

Adenosine Triphosphate↗