Spino‐dendritic cross‐talk in rodent Purkinje neurons mediated by endogenous Ca²⁺‐binding proteins

The continuing disappearance of “pure” Ca2+ buffers

“…In a model study, the spino-dendritic coupling in Purkinje cells and the role for dendritic Ca 2+ homeostasis and downstream signaling cascades was investigated using data obtained in PV-/-and CB-D28k-/-PV-/-mice [156]. CB-D28k is the more important "Ca 2+ transporter" than PV that, by buffered diffusion, also transiently increases [Ca 2+ ] i in dendritic shafts.…”

Localization of Calbindin-D28k and Calretinin in the Brain of Dermophis Mexicanus (Amphibia: Gymnophiona) and Its Bearing on the Interpretation of Newly Recognized Neuroanatomical Regions

“…Specifically, CB is a good marker of Purkinje cells [Fortin et al, 1998;Schmidt et al, 2005Schmidt et al, , 2007, whereas CR is found mainly in other cell types as granular [Gall et al, 2003], unipolar, brush, and Lugaro cells Schiffmann et al, 1999], except in primates where some subpopulations of Purkinje cells are CRir [Fortin et al, 1998]. In all species of amphibians studied so far CB is present in Purkinje cells and some granule cells [Uray et al, 1998;Uray and Gona, 1999;Morona and González, 2009] and particularly in Rana but not in Xenopus laevis, and urodeles Purkinje cells contain CR [Necchi et al, 1999;Uray and Gona, 1999;Morona and González, 2009].…”

“…However, the dissimilarities in CB and CR sequence [Parmentier, 1990] reflect functional and evolutionary differences between the two proteins in terms of adaptation to different targets [Schwaller et al, 2002;Palczewska et al, 2003]. CR is considered a pure Ca 2+ buffer which acts as passive modulator of the cytosolic calcium levels [Schmidt et al, 2007], whereas CB acts as a sensor that regulates the degradation of inositol messengers in an activity-dependent manner [Schmidt et al, 2005] and has a neuroprotective capability to prevent degeneration [Wang et al, 2008]. Thus, each protein seems to play specific roles in different neuron subsets.…”

Cytosolic Ca2+ Buffers

“…Thus, in a resting cell (e.g., muscle fibers, neurons), Ca 2þ buffers are mostly in the Ca 2þ -free form. It is the kinetics of various Ca 2þ buffers that strongly affect the spatiotemporal aspects of Ca 2þ signals, in particular, in excitable cells (Schmidt et al 2007b;Schmidt and Eilers 2009;Schwaller 2009 (Table 1). The ratio between high:intermediate affinity sites is either 3:1 or 2:2.…”

“…This indicates that the slow diffusion of Ca 2þ ions in a resting cell ([Ca 2þ ] i % 50 nM) is caused by slowly mobile or immobile buffers "acting like velcro" for Ca 2þ ions, limiting the effective range of an unbuffered free Ca 2þ ion to %0.1 mm. Thus, the range of Ca 2þ can be increased by buffered diffusion, that is, mobile Ca 2þ buffers acting as shuttles transporting Ca 2þ through the "mesh of immobile buffers" (Schmidt et al 2007b). …”