IDENTIFICATION, EXPRESSION PATTERN AND POTENTIAL ACTIVITY OF NA CA EXCHANGER ISOFORMS IN RAT PANCREATIC B-CELLS/

In the pancreatic B-cell, Na/Ca exchange displays a quite high capacit y and participates in the control of cytosolic free Ca2+ concentration . The Na/Ca exchanger was recently cloned in various tissues. Two gene s coding for two different exchangers (NCX1 and NCX2) have been identi fied and evidence for several isoforms for NCX1 shown. To characterize the isoform(s) expressed in pancreatic B-cells, a RT-PCR analysis was performed on mRNA from rat pancreatic islets, purified B-cells and in sulinoma B-cells (RINm5F cells). PCR amplification did not yield the e xpected NCX2 DNA fragment but yielded 2 NCX1 bands, corresponding to N aCa3 and NaCa7, in the three preparations. NaCa3 and NaCa7 were equall y expressed in pancreatic islets and purified B-cells. In RINm5F cells , NaCa3 expression did not differ from that in islet and purified B-ce lls but NaCa7 was 3 times less expressed. This lower expression was ac companied by a 3 times lower Na!Ga exchange activity in RINm5F cells c ompared to islet cells. Our data indicate the existence of 2 NCX1 isof orms but not of NCX2 in pancreatic B-cells. The difference in both the expression patterns of NCX1 isoforms and the activity of Na/Ca exchan ge in islet cells and RINm5F cells is compatible with a difference in activity between NaCa3 and NaCa7.