PLASMA-MEMBRANE CALCIUM-ATPASE ISOFORM EXPRESSION IN CULTURED RAT MESANGIAL CELLS

The maintenance of intracellular ionized calcium (iCa(2+)) in the subm icromolar range is important for mesangial cell (MC) function, and, as in most mammalian cells, plasma membrane Ca2+-ATPases (PMCA) play an important role in the homeostatic process. Molecular studies have demo nstrated four PMCA isoforms, each with multiple splice variants. The p resent study examines the expression of PMCA isoforms and calmodulin-b inding region splice variants in cultured MC from Sprague-Dawley rats and from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats before and after the onset of hypertension in SHR. Using reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot ana lyses, we have demonstrated PMCA1, -3, and -4, but not PMCA2, to be pr esent in MC from these rat strains. Splice variant analysis revealed P MCA1a and -1b, PMCA3a, -3b, and -3c, and PMCA4a and -4b to be expresse d in MC from all three strains. The relative quantities of PMCA1 and P MCA4 mRNA were not different in age-matched SHR vs. WKY rats, correlat ing with similar iCa(2+) measurements. The expression of all three iso forms declined with age in SHR and WKY.