Effect of in vivo changes in phospholipid composition on liver microsomal calcium transport

Potential-dependent Ca channels of neurons in the mollusc Lymnaea stagnalis in aging: effect of norepinephrine

During aging changes occur in the function of potential-dependent Ca channels of plasmic membrane of identified neurons in the mollusc Lymnaea stagnalis, i.e. the value of Ca inward current of neurons in old vs. adult molluscs was much higher at holding potential -50 - -30 mV. When held at -20 mV, the amplitude of Ca current decreased in the neurons of old molluscs, but continued to increase in those of adult molluscs. Various populations of potential-dependent Ca channels are assumed to have irregular age-related changes. The norepinephrine-induced inhibition of Ca current was more significant in old vs. adult molluscan neurons.

Activity of liver microsomal Ca2+-ATPase in relation to perturbation of membrane hydrophobic interactions induced by methoxybenzene derivatives and n-aliphatic alcohols

Changes in the activity of liver microsomal Ca2+-ATPase were studied in the presence of two series of lipophilic compounds: four flavouring substances derived from methoxybenzene and four n-aliphatic alcohols. With each compound the activity was stimulated at lower concentrations and inhibited at higher concentrations. The linear relationship between equiactive concentrations of the compounds and their partition coefficients showed that the enzyme activity was modulated by perturbation of membrane hydrophobic interactions. Measurements carried out by electron-spin resonance (ESR) showed evidence of a decrease in the membrane order induced by these compounds. However, results obtained with the methoxybenzene derivatives showed that the modification in ATPase activity cannot be directly related to the decrease in membrane order. This decrease did not only reflect perturbation of hydrophobic interactions.

Activation of Ca2+-stimulated ATPase by phospholipid N-methylation in cardiac sarcoplasmic reticulum

Incubation of cardiac sarcoplasmic reticulum (SR) in the presence of S-adenosyl-L-methionine, a methyl donor for the enzymatic N-methylation of phosphatidylethanolamine, increased Ca2+-stimulated ATPase activity. The increase in Ca2+-ATPase activity was not due to changes in the affinity for Ca2+ and was prevented by methyl acetimidate, an inhibitor of phospholipid N-methylation. The results suggest a possible regulatory role of phospholipid N-methylation in SR Ca2+-pump mechanism.