Spatiotemporal dynamics of intracellular calcium during speed tuning for directionality: the initial stage of cardinal direction selectivity

N.L. Iannella and R.R. Poznanski

Detecting moving objects is crucial in the animal kingdom and is fundamental to vision. In the vertebrate retina, starburst amacrine cells are directionally selective in terms of their calcium responses to stimuli that move centrifugally from the soma. The mechanism by which starburst amacrine cells show calcium bias for centrifugal motion is still to be determined. Recent morphological studies using fluorescent microscopy and immunostaining have shown that the endoplasmic reticulum is omnipresent in the soma, extending to the distal processes of starburst amacrine cells. Electron microscopy for ChAT SAC in adult rat retina unequivocally proves the presence of local endoplasmic reticulum. The submicron in diameter dendrites implies that the endoplasmic reticulum is not luminally connected between the soma and the distal tips. We construct a computational model of SAC dendrites with ER to simulate the Ca2+-induced Ca2+ release (CICR)-based calcium waves in the presence of unsaturated buffer to test the hypothesis that the CICR mechanism can sustain constant calcium wave propagation in the centrifugal direction...