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The effects of glucagon and vasopressin, singly or together, on cytosolic free Ca2+ concentration [( Ca2+]i) and on the 45Ca2+ efflux were studied in isolated rat liver cells. In the presence of 1 mM external Ca2+, glucagon and vasopressin added singly induced sustained increases in [Ca2+]i. The rate of the initial fast phase of the [Ca2+]i increase and the magnitude of the final plateau were dependent on the concentrations (50 pm-0.1 microM) of glucagon and vasopressin. Preincubating the cells with a low concentration of glucagon (0.1 nM) for 2 min markedly accelerated the fast phase and elevated the plateau of the [Ca2+]i increase caused by vasopressin. In the absence of external free Ca2+, glucagon and vasopressin transiently increased [Ca2+]i and stimulated the 45Ca2+ efflux from the cells, indicating mobilization of Ca2+ from internal store(s). Preincubating the cells with 0.1 nM-glucagon accelerated the rate of the fast phase of the [Ca2+]i rise caused by the subsequent addition of vasopressin. However, unlike what was observed in the presence of 1 mM-Ca2+, glucagon no longer enhanced the maximal [Ca2+]i response to vasopressin. In the absence of external free Ca2+, higher concentrations (1 nM-0.1 microM) of glucagon, which initiated larger increases in [Ca2+]i, drastically decreased the subsequent Ca2+ response to vasopressin (10 nM). At these concentrations, glucagon also decreased the vasopressin-stimulated 45Ca2+ efflux from the cells. It is suggested that, in the liver, glucagon accelerates the fast phase and elevates the plateau of the vasopressin-mediated [Ca2+]i increase respectively by releasing Ca2+ from the same internal store as that permeabilized by vasopressin, probably the endoplasmic reticulum, and potentiating the influx of extracellular Ca2+ caused by this hormone.

Brevibacterium linens is a major component of red-smear cheese microflora and imparts color to the cheese rind. The present study was done to evaluate carotenoid contents in 29 strains of this bacterium and to relate the color of the strains to the carotenoids present. A spectrocolorimeter was used to determine the color, and the carotenoid contents were determined by spectrophotorimetric measurement at 450 nm. Regression analysis was carried out on the color values a*, b*, and C* to determine which color value could be used to express the contents of carotenoids in B. linens biomass. The C* color value appeared to be the best estimate for correlation.

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The action of alpha 1-adrenergic agonists (noradrenaline in the presence of propranolol), vasopressin and angiotensin on the intracellular free Ca2+ concentration, [Ca2+]i, was determined by using the fluorescent dye quin2 in isolated rat liver cells. In the presence of external Ca2+ (1.8 mM), 1 microM-noradrenaline induced an increase in [Ca2+]i up to about 800 nM without apparent delay, whereas 10 nM-vasopressin and 1 nM-angiotensin increased [Ca2+]i to values higher than 1500 nM with a lag period of about 6s. The successive addition of the hormones and of their specific antagonists indicated that the actions of the three Ca2+-mobilizing hormones occurred without apparent desensitization (over 6 min) and via independent receptors. The relative contributions of internal and external Ca2+ pools to the cell response were determined by studying the hormone-mediated [Ca2+]i increase and glycogen phosphorylase activation in low-Ca2+ media (22 microM). In this medium: (1) [Ca2+]i was lowered and the hormones initiated a transient instead of a sustained increase in [Ca2+]i; subsequent addition (2 min) of a second hormone promoted a lesser increase in [Ca2+]i; in contrast, the subsequent addition (2 min) of Ca2+ (1.8 mM) caused [Ca2+]i to increase to a value close to that initiated by the hormone in control conditions, the amplitude of the latter response being dependent on the concentration of Ca2+ added to the medium; (2) returning to normal Ca2+ (1.8 mM) restored the resting [Ca2+]i and allowed the hormone added 2 min later to promote a large increase in [Ca2+]i whose final amplitude was also dependent on the concentration of Ca2+ added beforehand. Similar results were found when the same protocol was applied to the glycogen phosphorylase activation. It is concluded that Ca2+ influx is required for a maximal and sustained response and to reload the hormone-sensitive stores.

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