PBIO SEMINAR SERIES

CaBP4, a neuronal calcium-binding protein essential for photoreceptor synaptic function

October 15, 2009

Francoise Haeseleer
Physiology and Biophyics, University of Washington

Host: Stan Froehner

CaBP4 is a member of the CaBP subfamily of calmodulin-like Ca2+-binding proteins. CaBPs are expressed in neurons and regulate proteins that are also modulated by calmodulin. CaBP4 is expressed in retinal photoreceptors and in cochlear inner hair cells. It interacts with L-type voltage-dependent Ca2+ channels (VDCCs) and modulates their function. CaBP4 shifts the activation range of the recombinant Cav1.4 L-type VDCC to hyperpolarized voltages in transfected cells. A similar effect of CaBP4 on channel activation in photoreceptors would potentially support sustained glutamate release from photoreceptor terminals in the dark. CaBP4 is essential for the development and/or maintenance of the photoreceptor output synapse, probably through modulation of photoreceptor Ca2+ channels and neurotransmitter release. In the cochlea, CaBP4 can modulate the Cav1.3 channel, the major VDCC expressed in the inner hair cells. As photoreceptor and bipolar cells, inner hair cells have highly specialized glutamatergic ribbon synapses. Therefore, CaBP4 might have a key role in the regulation of presynaptic Ca2+ signaling at ribbon synapses and thus, modulate sensory transmission.