The invasion pore induced by Toxoplasma gondii

To survive, obligate intracellular apicomplexan parasites must invade host cells. For Toxoplasma gondii , a first indication of invasion is a transient breach in host cell permeability that precedes parasite entry. Here, a time-series analysis using novel filtering algorithms was performed on new electrophysiological data acquired at sub-200 μs time resolution. The analysis revealed an underlying structure to the parasite-induced conductance changes: conductance changes are consistent with a rapid insertion, then slower removal, blocking, or inactivation of quantal conductance elements. This quantal element was best described by a Gaussian distribution with mean of 0.26 nS (width 0.03 nS), which is like the conductance of another apicomplexan protein translocon, EXP2. The quantal conductance observed during interactions with parasites depleted of the rhoptry neck protein RON2, a central component of the moving junction between the parasite and the host cell during invasion, had a different Gaussian distribution (mean 0.19 nS, width 0.03 nS) supporting the hypothesis that RON2 contributes to the poration process or the passage of conductive elements through the pore.