The use of transgenic mouse models to reveal the functions of Ca2 + buffer proteins in excitable cells

BackgroundCytosolic Ca^2 + buffers are members of the large family of Ca^2 +-binding proteins and are essential components of the Ca^2 + signaling toolkit implicated in the precise regulation of intracellular Ca^2 + signals. Their physiological role in excitable cells has been investigated in vivo by analyzing the phenotype of mice either lacking one of the Ca^2 + buffers or mice with ectopic expression.Scope of ReviewIn this review, results obtained with knockout mice for the three most prominent Ca^2 + buffers, parvalbumin, calbindin-D28k and calretinin are summarized.Major ConclusionsThe absence of Ca^2 + buffers in specific neuron subpopulations, and for parvalbumin additionally in fast-twitch muscles, leads to Ca^2 + buffer-specific changes in intracellular Ca^2 + signals. This affects the excitation–contraction cycle in parvalbumin-deficient muscles, and in Ca^2 + buffer-deficient neurons, properties associated with synaptic transmission (e.g. short-term modulation), excitability and network oscillations are altered. These findings have not only resulted in a better understanding of the physiological function of Ca^2 + buffers, but have revealed that the absence of Ca^2 + signaling toolkit components leads to protein-and neuron-specific adaptive/homeostatic changes that also include changes in neuron morphology (e.g. altered spine morphology, changes in mitochondria content) and network properties.General SignificanceThe complex phenotype of Ca^2 + buffer knockout mice arises from the direct effect of these proteins on Ca^2 + signaling and moreover from the homeostatic mechanisms induced in these mice. For a better mechanistic understanding of neurological diseases linked to disturbed/altered Ca^2 + signaling, a global view on Ca^2 + signaling is expected to lead to new avenues for specific therapies. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signaling.