Introduction

1. Coelenterazine + O2 Apoaequorine-Coelenterazine Apoaequorine + 3Ca2+ Apoaequorine Coelenteramide+ CO2 Altered Intracellular Ca2+ Release in Fibroblasts from Presenilin/ Presenilin2 double knockout and Amiloid Precursor Protein knockout mice. N. Nadif Kasri‡, L. Verbert‡, K. Van Acker, J.B. Parys‡, G. Callewaert‡, L. Missiaen‡, B. De Strooper and H. De Smedt‡ ‡Laboratory of Physiology, K.U.Leuven Campus Gasthuisberg, 3000 Belgium Introduction Presenilins (PS1 and PS2) are a part of the -secretase complex which is responsible for the proteolysis of the amyloid precursor protein (APP) and the subsequent formation of the -amyloid peptide (A). Accumulation of A in extracellular plaques is thought to be an important trigger in the pathogenesis of Alzheimer’s Disease. One of the cellular disfunctions that take place is a disturbed Ca2+ homeostasis. Mutations in the PS genes that form a major cause of an early onset form of familial Alzheimer’s disease (FAD), cause an increased IP3-mediated Ca2+ release from intracellular Ca2+ stores. A suppression of the capacitive calcium entry (CCE), a Ca2+ entry as a reaction on the depletion of the stores, was also observed. Some experiments show that an overfilling of the ER is a common feature of both effects. Using the Ca2+ sensitive bioluminescence protein aequorin, we’ve been able to confirm in a direct manner that PS influence luminal Ca2+ concentrations. The 45Ca2+ flux technique has given us the oppurtunity to report that in fibroblasts deficient in APP or one or both of the PS, a redistribution of Ca2+ over the stores occurs. Using the same technique, we’ve detected an increased IP3 sensitivity in PS deficient cells. Our results also show that the effect of farmacological inhibition of PS (using the -secretase Inhibitor X) on the luminal Ca2+ concentrations doesn’t occur in APPko cells, and thus presumably occurs via the formation of APP metabolites. Methods