Evoked Centripetal Ca2+ Activation in Cardiac Purkinje Cells: CICR or Ca2+ Diffusion?

Abstract

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder. Familial AD (FAD) mutations in presenilins have been linked to Ca 2þ signaling abnormalities. Presenilins (PS) are 50 kDa proteins in the endoplasmic reticulum (ER) membrane. The cleaved presenilins are well known as catalytic components of a gamma-secretase, which cleaves the amyloid precursor protein (APP) and releases the amyloid beta-peptide. In addition uncleaved presenilins function as passive ER Ca 2þ leak channels which control steadystate ER Ca 2þ levels. It was found that many FAD mutations in presenilins result in loss of ER Ca 2þ leak function, leading to ER Ca 2þ overload and supranormal Ca2þ release from the ER. The ER Ca 2þ leak function of presenilins is independent of their gamma-secretase activity. We suggested that presenilins affect store-operated calcium influx (SOC) by controlling the filling state of ER Ca 2þ stores. To determinate the influence of FAD presenilins mutations on SOC we performed a series of patch-clamp experiments in whole-cell mode. PS1-M146V and PS1-DE9 mutants have been shown to have loss and gain of ER Ca 2þ leak channel function respectively. A decrease in maximum amplitude and speed of SOC current activation was observed in SK-N-SH neuroblastoma cells and primary culture of rat hippocampal neurons transfected with PS1-M146V mutant comparing to wild type PS1 transfected cells. An increase in maximum amplitude and speed of SOC current activation was observed in cells transfected by PS1-DE9 mutant comparing to wild type PS1. In experiments with triple transgenic AD mice hippocampal neurons (3XTg mice; KI-PS1M146V, Thy1-APPKM670/671NL, Thy1-tauP301L) the maximum amplitude of SOC were decreased comparing to WT, but the speed of activation was the same for 3XTg and WT hippocampal neurons. Electrophysiological properties of all impaired SOCs suggest that TRPC1 is the main target of presenilins FAD mutations affect.