Calcium transport by plasma membranes from a glucose-responsive rat insulinoma

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Inside-out plasma membrane vesicles from a glucose-responsive rat insulinoma showed an ATP- and Mg2+-dependent uptake of Ca2+. The Km (concentration giving half-maximal activity) for Ca2+ was 60 nM. In the presence of 0.4 μM free Ca2+, the Km, for ATP was 15 μM, and the Km, for Mg2+ was 4 μM. Glucose (30 mM) decreased Ca2+ uptake by 50%, while other insulin secretagogues had no effect, except for glyceraldehyde, which stimulated Ca2+ uptake. Calmodulin increased the uptake of Ca2+, while trifluoperazine and vanadate inhibited the uptake. The Ca2+- and Mg2+-dependent ATPase from this tumor has a 10- to 20-fold higher requirement for Ca2+, which suggests that this enzyme is not responsible for Ca2+ transport, rather, Ca2+ transport activity represents only a small fraction of the total Ca2+-ATPase activity. The physiological importance of Ca2+ transport in insulin secretion is evident from the inhibition of Ca2+ uptake by glucose, which leads to a decrease in Ca2+ efflux from the cell. This inhibition would lead to an increase in intracellular free Ca2+ and insulin release.

Original languageEnglish (US)
Pages (from-to)1381-1384
Number of pages4
Issue number3
StatePublished - Mar 1991
Externally publishedYes

ASJC Scopus subject areas

  • Endocrinology


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