Uptake of calcium by pancreatic islet cell microsomes: inhibition by a monoclonal antibody to heart sarcoplasmic reticulum.

The uptake of Ca2+ by microsomes is thought to participate in the control of cytosolic Ca2+ activity in the insulin-producing pancreatic B-cell. In order to study such a phenomenon methods were developed to isolate microsomes from rat parotid cells, pancreatic islets and tumoral islet cells of the RINm5F line. In the latter case, a subcellular microsomal fraction was prepared in which the ratio of microsomal/mitochondrial enzyme markers, as well as that of ruthenium red-resistant/sensitive 45Ca2+ uptake was 20 times higher than in the corresponding mitochondrial subcellular fraction. The ATP-dependent net uptake of 45Ca2+ by RINm5F cell microsomes was inhibited at low temperature and by either vanadate or a monoclonal antibody to dog heart sarcoplasmic reticulum. Although the uptake of Ca2+ by microsomes may account for only a minor fraction of ATP consumption, its synarchistic regulation by ATP and Ca2+, at close-to-physiological concentrations, appeared well suited to play a major regulatory role in the control of cytosolic Ca2+ activity in intact islet cells.