Expression of multiple plasma membrane Ca2+-ATPases in rat pancreatic islet cells

When stimulated by glucose, the pancreatic beta-cell displays large oscilla tions of intracellular free Ca2+ concentration ([Ca2+](i)). To control [Ca2 +](i), the beta-cell must be equipped with potent mechanisms for Ca2+ extru sion. We studied the expression of the plasma membrane Ca2+-ATPases (PMCA) in three insulin secreting preparations (a pure beta-cell preparation, RINm 5F cells and pancreatic islet cells), using reverse-transcribed PCR, RNase protection assay and Western blotting. The four main isoforms, PMCA1, PMCA2 , PMCA3 and PMCA4 were expressed in the three preparations. Six alternative splice mRNA variants, characterized at splice sites A, B and C were detect ed in the three preparations (rPMGA1xb, 2yb, 2wb, 3za, 3zc, 4xb), plus two additional variants in pancreatic islet cells (PMCA4za, 1xkb). The latter v ariant corresponded to a novel variant of rat PMCA1 gene lacking the exon c oding for the 10th transmembrane segment, at splice site B. At the mRNA and protein level, five variants predominated (1xb, 2wb, 3za, 3zc, 4xb), whils t one additional isoform (4za), predominated at the protein level only. Thi s provides the first evidence for the presence of PMCA2 and PMCA3 isoforms at the protein level in non-neuronal tissue. Hence, the pancreatic beta-cel l is equipped with multiple PMCA isoforms with possible differential regula tion, providing a full range of PMCAs for [Ca2+](i) regulation. (C) 2000 Ha rcourt Publishers Ltd.