Altered protein kinase C activation of Na+/Ca2+ exchange in mesangial cells from salt-sensitive rats

Academic Article

Abstract

  • The purpose of these studies was to determine whether there is a defect in protein kinase C (PKC) regulation of the Na /Ca exchanger in cultured mesangial cells (MC) from Dahl/Rapp salt-sensitive (S) and salt-resistant (R) rats. R and S MCs were cultured, grown on coverslips, and loaded with fura 2 for measurement of single cell cytosolic calcium concentration ([Ca ](i)) in a microscope-based photometry system. Studies were performed in cells that were exposed to serum (serum fed) and in cells that were serum deprived for 24 h. Baseline [Ca ](i) values measured in a Ringer solution containing 150 mM NaCl were similar between R and S MCs in both serum-fed and serum- deprived groups, although baseline [Ca ](i) values were uniformly higher in the serum-deprived groups. Exchanger activity was assessed, by reducing extracellular Na (Na(e)) from 150 to 2 mM, which resulted in movement of Na out of and Ca into these cells (reverse-mode Na /Ca exchange). PKC was activated in these cells with 15-min exposure to 100 nM phorbol 12- myristate 13-acetate (PMA). In the absence of PMA, the change in [Ca ](i) (Δ[Ca ](i)) with reduction in Na(e) was similar between R and S MCs in both serum-fed and serum-deprived groups, although the magnitude of Δ[Ca ](i) was enhanced by serum deprivation. In both serum-fed and serum- deprived groups, PMA significantly increased Δ[Ca ](i) in R but not S MCs. Upregulation of exchanger activity in R MCs could be abolished by prior 24-h exposure to PMA, a maneuver that downregulates PKC activity. Other studies were performed to evaluate exchanger protein expression using monoclonal and polyclonal antibodies. Immunoblots of PMA-treated cells revealed an increase in the levels of 70- and 120-kDa proteins in the crude membrane fraction of R but not S MCs, an increase which was abrogated by prior 24-h PMA pretreatment and corresponded to reduction in the 70-kDa protein in the crude cytosolic fraction. These data demonstrate that PKC enhances Na /Ca exchange activity in MCs from R but not from S rats, suggesting that there may be a defect in the PKC-Na /Ca exchange regulation pathway in MCs of S rats. + 2+ 2+ 2+ 2+ + 2+ + 2+ 2+ 2+ 2+ 2+ + 2+ + 2+
  • Digital Object Identifier (doi)

    Pubmed Id

  • 23448285
  • Author List

  • Mashburn NA; Unlap MT; Runquist J; Alderman A; Johnson GVW; Bell PD
  • Volume

  • 276
  • Issue

  • 4 45-4