  We give a review of the current state of the art of data-driven modelling of
the inositol trisphosphate receptor (IPR). After explaining that the IPR plays
a crucial role as a central regulator in calcium dynamics, several sources of
relevant experimental data are introduced. Single ion channels are best studied
by recording single-channel currents under different ligand concentrations via
the patch-clamp technique. The particular relevance of modal gating, the
spontaneous switching between different levels of channel activity that occur
even at constant ligand concentrations, is highlighted. In order to investigate
the interactions of IPRs, calcium release from small clusters of channels,
so-called calcium puffs, can be used. We then present the mathematical
framework common to all models based on single-channel data, aggregated
continuous-time Markov models, and give a short review of statistical
approaches for parameterising these models with experimental data. The process
of building a Markov model that integrates various sources of experimental data
is illustrated using two recent examples, the model by Ullah et al. and the
"Park-Drive" model by Siekmann et al., the only models that account for all
sources of data currently available. Finally, it is demonstrated that the
essential features of the Park-Drive model in different models of calcium
dynamics are preserved after reducing it to a two-state model that only
accounts for the switching between the inactive "park" and the active "drive"
mode. This highlights the fact that modal gating is the most important
mechanism of ligand regulation in the IPR. It also emphasises that data-driven
models of ion channels do not necessarily have to lead to detailed models but
can be constructed so that relevant data is selected to represent ion channels
at the appropriate level of complexity for a given application.
