Reduced IP3 sensitivity of IP3 receptor in Purkinje neurons

The inositol 1,4,S-trisphosphate receptor (IP3R) is highly expressed in Pur kinje neurons (PNs) and is thought to be essential for the induction of lon g-term depression at parallel-fiber-PN synapses. Here, by imaging the fluor escence intensity of the low-affinity Ca2+ indicator inside the Ca2+ stores in the permeabilized single PNs, we analyzed the kinetics of Ca2+ release via the IP3R in controlled cytoplasmic environments. The rate of Ca2+ relea se is dependent on the IP3 concentration with an EC50 of 25.8 muM, which is > 20-fold greater than that of the IP3R in the isolated preparations or in peripheral cells. This property would be advantageous in inducing the rele ase of Ca2+ in a localized space adjacent to the site of synaptic inputs. N euroReport 12:2647-2651 (C) 2001 Lippincott Williams & Wilkins.