Selective decrease of mRNAs encoding plasma membrane calcium pump isoforms2 and 3 in rat kidney

Background. Although the existence of multiple isoforms of plasma membrane calcium ATPase (PMCA) is now well documented, their biological functions ar e not yet known. In this study, we set out to investigate the potential rol e of PMCA isoforms, previously identified in renal cortical tissue, in tubu lar reabsorption of calcium (Ca2+). Methods. With use of reverse transcription-polymerase chain reaction analys is, we determined levels of mRNAs encoding isoforms of PMCA1 through PMCA4 in renal cortex, liver, and brain of rats with hypercalciuria induced by fe eding with a low-phosphate diet (LPD) as compared with Ca2+-retaining rats that were fed a high-phosphate diet (HPD). Results. We observed that in hypercalciuric LPD-fed rats, the mRNAs encodin g isoforms PMCA2b and PMCA3(a + c) are significantly lower (Delta approxima tely -50%) than in HPD-fed hypocalciuric rats, whereas no changes in mRNAs encoding isoforms PMCA1b and PMCA1b were observed, and mRNA encoding calbin din 28 kDa was increased. On the other hand, the content of mRNAs encoding PMCA2b and PMCA2b(a; c) in liver and brain, respectively, was not changed. Conclusion. These findings are evidence that expression of PMCA isoforms in the kidney can be selectively modulated in response to pathophysiologic st imuli. The association of a decrease in mRNA encoding PMCA2b and PMCA3(a c) with hypercalciuria suggests that the two PMCA isoforms may be operant i n tubular reabsorption of Ca2+ and its regulation.