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Biomedical subjects

K Kumada

Publications and source records attributed to K Kumada.

At least 163 records · Page 9Linked to original sources
PubMed1985

Effects of calmodulin antagonists and calmodulin on phospholipid base-exchange activities in rabbit platelets.

Effects of various calmodulin antagonists and calmodulin on the incorporation of serine, ethanolamine and choline into the corresponding phospholipids, such as phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine by Ca2+-stimulated base-exchange reactions in rabbit platelet membranes were studied. Under a Ca2+-EGTA buffer system, the incorporation of three bases were stimulated by Ca2+ in a biphasic manner. Minimum requirement of free Ca2+ for the reactions was found to be around 0.5 microM and maximal incorporation took place at high Ca2+ concentrations (3-5 mM). Various calmodulin antagonists such as chlorpromazine, trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide, not only activated the three reactions but also greatly enhanced their sensitivity to Ca2+ (K0.5, 0.1-0.3 microM). In the absence of Ca2+, however, the drugs did not show any effect on the reactions. The concentrations of the drugs required for half maximal stimulation were approx. 30-40 microM. Although platelet membranes contained endogenous calmodulin (0.3-0.6 microgram/mg of membrane protein), the addition of exogenous calmodulin inhibited choline exchange activity but had no or little effect on serine or ethanolamine exchange activity. The results suggest that in the presence of low Ca2+ concentrations, these drugs markedly stimulate base-exchange activities, and choline exchange activity may be regulated by calmodulin.

Animals↗
PubMed1983

Enzymatic properties of phospholipid methylation in rabbit platelets.

The enzymatic properties of phospholipid methylation in rabbit platelets were examined using S-adenosyl-L-[methyl-3H]methionine as a substrate. pH optimum for the methylation was around 10.5 under Tris-HCl and glycine-NaOH buffer systems. When Tris-HCl buffer was replaced by phosphate buffer, pH optimum shifted to around 8.0 and the methylation was increased approximately threefold, compared with that in the case of Tris-HCl buffer at pH 8.0. The formation of the 3H-methylated phospholipids was increased by addition of exogenous phosphatidyl-N-monomethylethanolamine or phosphatidyl-N,N-dimethylethanolamine, intermediates of the biosynthesis of phosphatidylcholine from phosphatidylethanolamine. However, the increase in product formations by addition of exogenous intermediates was all but equal under Tris-HCl and phosphate buffer systems at pH 8.0. These results suggest that phosphate ion stimulates the first step of the successive methylation to form phosphatidyl-N-monomethylethanolamine from phosphatidylethanolamine. The methylation in platelets was inhibited to 30% of the basal value with Ca2+ (0.2 mM). However, Ca2+ showed different effects on the methylation in various tissues (activation to 150% of the basal value in the adrenal gland and slight inhibition to 82-88% of corresponding basal values in the liver, lung, kidney and brain).

Animals↗
PubMed1980

Dissecting aneurysm during pregnancy and the puerperium.

According to Schnitker, Mandel, Hirst and their associates, approximately half of the dissecting aneurysms in women under 40 years of age are associated with pregnancy. This significant relationship between dissecting aneurysm and pregnancy has been discussed by considering hemodynamic stress and also the hormonal changes of pregnancy. In this report, we describe five patients with dissecting aneurysm during pregnancy or the puerperium, review the literature and discuss the influence of pregnancy on the pathogenesis of this disease.

Adult↗
PubMed1980

A serious problem of the heated thermocouple flowmeter.

In the measurement of regional blood flow with heated thermocouple flowmeter, we frequently observed puzzling phenomenon that the measured values were augmented while the flow was actually diminished and vice versa (Inversion). "Inversion" was directly attrebutable to the structure of the thermocouple probe. A countermeasure against "Inversion" was found to lie in the arrangement of the hot junction in the center of the heater, and in practical application, it must be checked by stopping the flow at each measurement. Overcoming this technical liability should pave the way for a marked improvement in the reliability of this method which, despite possessing many excellent characteristics for determining regional blood flow, is not widely used.

Animals↗