Ionophore-resistant mutant of Toxoplasma gondii reveals involvement of a sodium/hydrogen exchanger in calcium regulation

J Cell Biol. 2004 Jun 7;165(5):653-62. doi: 10.1083/jcb.200309097. Epub 2004 Jun 1.

Abstract

Calcium is a critical mediator of many intracellular processes in eukaryotic cells. In the obligate intracellular parasite Toxoplasma gondii, for example, a rise in [Ca2+] is associated with significant morphological changes and rapid egress from host cells. To understand the mechanisms behind such dramatic effects, we isolated a mutant that is altered in its responses to the Ca2+ ionophore A23187 and found the affected gene encodes a homologue of Na+/H+ exchangers (NHEs) located on the parasite's plasma membrane. We show that in the absence of TgNHE1, Toxoplasma is resistant to ionophore-induced egress and extracellular death and amiloride-induced proton efflux inhibition. In addition, the mutant has increased levels of intracellular Ca2+, which explains its decreased sensitivity to A23187. These results provide direct genetic evidence of a role for NHE1 in Ca2+ homeostasis and important insight into how this ubiquitous pathogen senses and responds to changes in its environment.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amiloride / pharmacology
  • Animals
  • Calcimycin / pharmacology
  • Calcium / metabolism*
  • Calcium Signaling / drug effects
  • Calcium Signaling / genetics*
  • Cell Death / drug effects
  • Cell Death / genetics
  • Cell Membrane / drug effects
  • Cell Membrane / genetics
  • Cell Membrane / metabolism
  • Drug Resistance / genetics
  • Homeostasis / drug effects
  • Homeostasis / genetics
  • Ion Channels / drug effects
  • Ion Channels / genetics
  • Ion Channels / metabolism
  • Ionophores / pharmacology
  • Mutation / genetics*
  • Protons
  • Sodium-Hydrogen Exchangers / genetics
  • Sodium-Hydrogen Exchangers / metabolism*
  • Toxoplasma / drug effects
  • Toxoplasma / genetics*
  • Toxoplasma / metabolism*

Substances

  • Ion Channels
  • Ionophores
  • Protons
  • Sodium-Hydrogen Exchangers
  • Calcimycin
  • Amiloride
  • Calcium