Mechanism of sodium uptake in PNA negative MR cells from rainbow trout, Oncorhynchus mykiss as revealed by silver and copper inhibition

Greg Goss, University of Alberta
Kathleen Gilmour, University of Ottawa, Canada
Guy Hawkings, University of Alberta
Jonathan H. Brumbach, University of Alberta
Maily Huynh, University of Alberta
Fernando Galvez, Louisiana State University


The rate of acid-stimulated and phenamil-sensitive sodium (Na+) uptake was measured in three different cell lineages: pavement cells (PVC), total mitochondrion-rich (MR) cell populations, and peanut lectin agglutinin-negative mitochondrion-rich cells (PNA- MR) isolated from the rainbow trout gill epithelium. Despite the presence of basal levels of Na+ uptake in PVC, this transport was not enhanced by acidification, nor was it inhibited by independent treatment with bafilomycin (i.e., a V-type H+-ATPase inhibitor), phenamil (i.e., a specific inhibitor of ENaC), or Ag (a specific inhibitor of active Na+ transport in fish). In contrast, Na+ uptake in PNA- MR cells was increased by ~220% above basal levels following acidification of near 0.4 pH units in the presence of 1.0mM external Na+. Acid-stimulated Na+ transport was entirely inhibited by both phenamil and bafilomycin. Silver (Ag) and copper (Cu), which are known to interfere with active Na+ transport in fish, were also responsible for inhibiting acid stimulated Na+ uptake in PNA- MR cells, but by themselves had no effect on basal Na+ transport. Thus, we demonstrate that Ag specifically prevented acid-stimulated Na+ uptake in PNA- MR cells in a dose-dependent manner. We also demonstrate rapid (<1min) and significant inhibition of carbonic anhydrase (CA) by Ag in PNA- MR cells, but not in PVC. These data lend further support to the idea of a PNA- MR cell type as the primary site for Na+ uptake in the freshwater (FW) gill phenotype of rainbow trout. Moreover, these findings provide support for the importance of intracellular protons in regulating the movement of Na+ across the apical surface of the fish gill. © 2011 Elsevier Inc.