The incorporation of 32P from [gamma-32P]ATP into intracellular proteins was studied in electrically permeabilized rat islets of Langerhans. Ca2+ (10 microM), cyclic AMP (100 microM) and a protein kinase C-activating phorbol ester, phorbol 13-myristate 12-acetate (PMA; 100 nM) produced marked changes in the phosphorylation state of a number of proteins in permeabilized islets after incubation for 1 min at 37 degrees C. Ca2+ modified the effects of cyclic AMP and PMA on protein phosphorylation. Noradrenaline (10 microM) had no detectable effects on Ca2+-dependent protein phosphorylation, but significantly inhibited Ca2+-induced insulin secretion from electrically permeabilized islets. These results suggest that electrically permeabilized islets offer a useful model in which to study rapid events in protein phosphorylation as a mechanism of stimulus-secretion coupling. If the rapid Ca2+-induced effects on protein phosphorylation are involved in the control of insulin secretion, the results of this study also imply that part of the catecholamine inhibition of insulin secretion occurs at a stage in the secretory pathway beyond the activation of the regulated protein kinases.

1. Fatty acid synthesis de novo was measured in the perfused liver of fed mice. 2. The total rate, measured by the incorporation into fatty acid of (3)H from (3)H(2)O (1-7mumol of fatty acid/h per g of fresh liver), resembled the rate found in the liver of intact mice. 3. Perfusions with l-[U-(14)C]lactic acid and [U-(14)C]glucose showed that circulating glucose at concentrations less than about 17mm was not a major carbon source for newly synthesized fatty acid, whereas lactate (10mm) markedly stimulated fatty acid synthesis, and contributed extensive carbon to lipogenesis. 4. The identification of 50% of the carbon converted into newly synthesized fatty acid lends further credibility to the use of (3)H(2)O to measure hepatic fatty acid synthesis. 5. The total rate of fatty acid synthesis, and the contribution of glucose carbon to lipogenesis, were directly proportional to the initial hepatic glycogen concentration. 6. The proportion of total newly synthesized lipid that was released into the perfusion medium was 12-16%. 7. The major products of lipogenesis were saturated fatty acids in triglyceride and phospholipid. 8. The rate of cholesterol synthesis, also measured with (3)H(2)O, expressed as acetyl residues consumed, was about one-fourth of the basal rate of fatty acid synthesis. 9. These results are discussed in terms of the carbon sources of hepatic newly synthesized fatty acids, and the effect of glucose, glycogen and lactate in stimulating lipogenesis, independently of their role as precursors.

An increased turnover of phosphatidate and phosphatidyl inositol has been found in many tissues where hormones or neurotransmitters are postulated to raise Ca2+ influx, for example in smooth muscle. However, the relationship between changes in phospholipid metabolism and changes in Ca2+ permeability was unknown. Following recent reports on the interactions of Ca2+ with phosphatidic acid in membranes and artificial systems, we investigated the hypothesis that phosphatidate accumulation mediates the action of cholinergic and other stimuli on Ca2+ influx. We report here that synthesis and accumulation of phosphatidate was accelerated in smooth muscle cells stimulated by carbamylcholine with a similar time course to that of contraction. This alteration in phosphatidate metabolism does not seem to result from an increase in intracellular Ca2+ or depolarisation of the cell membrane. Furthermore, submicromolar concentrations of phosphatidate rapidly produce contractions of isolated smooth muscle cells. These results support the contention that cholinergic-induced changes in membrane Ca2+ permeability in smooth muscle could be mediated by phosphatidate accumulation.

1. Lipoproteins in the plasma of mice were characterized by agarose-gel chromatography and polyacrylamide-gel electrophoresis: genetically obese (ob/ob) mice exhibited hyperlipoproteinaemia (compared with lean mice), largely owing to an increase in the concentration of cholesterol in high-density lipoprotein. Plasma concentrations of triglyceride and phospholipid were not markedly increased in genetically obese mice. 2. The formation of glycerolipids in liver and plasma was investigated with (14)C-labelled precursors. The synthesis of hepatic triglyceride and phospholipid from glucose or palmitate was enhanced in ob/ob mice, compared with lean mice. The rate of entry of triglyceride into plasma, calculated from the time-course of incorporation of (14)C from [(14)C]palmitate into plasma triglyceride, was increased in ob/ob mice (0.5mumol of fatty acid/min, compared with 0.2 in lean mice). 3. The removal from plasma of murine lipoprotein triglyceride-[(14)C]fatty acid was increased in ob/ob mice (half-time 2.2min, compared with 7.2min in lean mice). Similar results were obtained with an injected lipid emulsion (Intralipid). 4. From these measurements, estimates of the rates of turnover of plasma triglyceride in mice (fed on a mixed diet, female, 3 months old) are about 1.0mumol of fatty acid/min in ob/ob mice, and 0.25 in lean mice. 5. The major precursor of hepatic and plasma triglyceride in lean and ob/ob mice was calculated to be plasma free fatty acid. 6. These results are discussed, in connexion with the role of the liver in triglyceride metabolism in mice, especially in relation to genetic obesity.