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At least 487 records · Page 27Linked to original sources
PubMed1985

The effects of maitotoxin on 45Ca2+ flux and hormone release in GH3 rat pituitary cells.

Maitotoxin has been reported to activate calcium channels and stimulate calcium-dependent functions in several tissues, but a thorough investigation of 45Ca2+ fluxes is lacking. To characterize the influence of maitotoxin on 45Ca2+ flux in greater detail, we incubated dispersed GH3 pituitary tumor cells in 45Ca2+ with maitotoxin and other agents affecting calcium channels. Within 10 sec of exposure, maitotoxin induced a net calcium influx in cells at isotopic equilibrium. Calcium uptake was concentration dependent between 0.4 and 40 ng/ml maitotoxin and was inhibited by antagonists of voltage-dependent calcium channels but not by inhibitors of sodium channels. PRL and GH release from perifused GH3 cells was stimulated within 1 min by maitotoxin. We conclude that maitotoxin causes a rapid, concentration-dependent influx of calcium through presumed voltage-dependent endogenous calcium channels, culminating in enhanced hormone release. This potent toxin may provide a more precise understanding of the role of calcium in the stimulus-secretion coupling process.

Animals↗
PubMed1980

The reproducibility of double-isotope deconvolution measurements of intestinal calcium absorption.

1. Radiocalcium absorption was measured in duplicate in 10 subjects by the double-isotope method, with calcium as the oral carrier (2.5 mmol). Analysis of variance gave 95% confidence limits for a single measurement of fractional absorption and maximum absorption rate in a given individual of +/- 16.5% of administered dose and +/- 18.2% of dose/h respectively. 2. The size of these within individual variations suggests that alterations in the rate of calcium absorption may contribute to the week-to-week stabilization of some other controlled variable, such as plasma concentration of calcium. 3. In six of the subjects, calcium absorption was also measured with calcium loads at concentrations of 0.5, 5.0 and 20 mmol. Significant falls in fractional absorption, maximum absorption rate and mean transfer rate occurred as the load increased, together with a rise in mean transit time. Although between-individual differences at a given load were considerable, given a single-test result with a known carrier load, it is possible to predict quite accurately the results which would be obtained if a different carrier load were to be given.

Analysis of Variance↗