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SummaryAging is a complex, multifactorial process. One of the features of normal aging of the brain is a decline in cognitive functions and much experimental attention has been devoted to understanding this process. Evidence accumulated in the last decade indicates that such functional changes are not due to gross morphological alterations, but to subtle functional modification of synaptic connectivity and intracellular signalling and metabolism. Such synaptic modifications are compatible with a normal level of activity and allow the maintenance of a certain degree of functional reserve. This is in contrast to the changes in various neurodegenerative diseases, characterized by significant neuronal loss and dramatic and irreversible functional deficit. This whole special issue has been initiated with the intention of focusing on the processes of normal brain aging. In this review, we present data that shows how subtle changes in Ca 2+ homeostasis or in the state of various Ca 2+ -dependent processes or molecules, which occur in aging can have significant functional consequences.

International audienceSphingosine 1-phosphate (S1P) receptor expression and the effects of S1P on migration were studied in one papillary (NPA), two follicular (ML-1, WRO) and two anaplastic (FRO, ARO) thyroid cancer cell lines, as well as in human thyroid cells in primary culture. Additionally, the effects of S1P on proliferation, adhesion and calcium signalling were addressed in ML-1 and FRO cells. All cell types expressed multiple S1P receptors. S1P evoked intracellular calcium signalling in primary cultures, ML-1 cells and FRO cells. Neither proliferation nor migration was affected in primary cultures, whereas S1P partly inhibited proliferation in ML-1 and FRO cells. Low nanomolar concentrations of S1P inhibited migration in FRO, WRO and ARO cells, but stimulated ML-1 cell migration. Consistently, S1P 1} and S1P 3}, which mediate migratory responses, were strongly expressed in ML-1 cells and S1P 2}, which inhibits migration, was the dominating receptor in the other cell lines. The migratory effect in ML-1 cells was mediated by G i} and phosphatidylinositol 3-kinase. Both S1P and the S1P 1}-specific agonist SEW-2871 induced Akt phosphorylation at Ser-473. However, SEW-2871 failed to stimulate migration, whereas the S1P 1}/S1P 3} antagonist VPC 23019 inhibited S1P-induced migration. The results implicate that aberrant S1P receptor expression may enhance thyroid cancer cell migration and thus contribute to the metastatic behaviour of some thyroid tumours

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The endoplasmic reticulum (ER) is a universal signalling organelle, which regulates a wide range of neuronal functional responses. Calcium release from the ER underlies various forms of intracellular Ca 2+ signalling by either amplifying Ca 2+ entry through voltage-gated Ca 2+ channels by Ca 2+ -induced Ca 2+ release (CICR) or by producing local or global cytosolic calcium fluctuations following stimulation of metabotropic receptors through inositol-1,4,5-trisphosphate-induced Ca 2+ release (IICR). The ER Ca 2+ store emerges as a single interconnected pool, thus allowing for a long-range Ca 2+ signalling via intra-ER tunnels. The fluctuations of intra-ER free Ca 2+ concentration regulate the activity of numerous ER resident proteins responsible for post-translational protein folding and modification. Disruption of ER Ca 2+ homeostasis results in the developing of ER stress response, which in turn controls neuronal survival. Altered ER Ca 2+ handling may be involved in pathogenesis of various neurodegenerative diseases including brain ischemia and Alzheimer dementia.

High resolution digital video imaging has been employed to monitor the spatial and temporal development of agonist‐induced cytosolic Ca2+ signals in fura 2‐loaded exocrine acinar cells. Enzymatically isolated mouse pancreatic and lacrimal acinar cells or small acinar cell clusters were used. These retain their morphological polarity so that the secretory granules in individual cells are located at one pole, the secretory pole. In acinar cell clusters the granules are located centrally, oriented to surround what would be in situ referred to as the lumen. In pancreatic and lacrimal acinar cells inositol‐1,4,5‐triphosphate‐generating agonists [acetylcholine (ACh) and cholecystokinin octapeptide (CCK) for the pancreas and ACh in the lacrimal gland] give rise to a rapidly spreading Ca2+ signal that is initiated at the secretory pole of the cells. The initial increase in [Ca2+]i in the luminal pole is independent of extracellular Ca2+ indicating that the earliest detectable intracellular Ca2+ release is specifically located at the secretory pole. In lacrimal acinar cells ATP acts as an extracellular agonist, independent of phosphoinositide metabolism to activate a receptor‐operated calcium influx pathway which, as for ACh, gives rise firstly to an increase in intracellular Ca2+ concentration in the secretory pole. We propose that this polar rise in intracellular Ca2+ concentration is due to Ca(2+)‐induced Ca2+ release. By contrast, when Ca2+ release and Ca2+ influx are induced in the absence of receptor activation by thapsigargin and ionomycin, the Ca2+ signal develops diffusely and slowly with no localization to the secretory pole.(ABSTRACT TRUNCATED AT 250 WORDS)

Agonist‐specific cytosolic Ca2+ oscillation patterns can be observed in individual cells and these have been explained by the co‐existence of separate oscillatory mechanisms. In pancreatic acinar cells activation of muscarinic receptors typically evokes sinusoidal oscillations whereas stimulation of cholecystokinin (CCK) receptors evokes transient oscillations consisting of Ca2+ waves with long intervals between them. We have monitored changes in the cytosolic Ca2+ concentration ([Ca2+]i) by measuring Ca2(+)‐activated Cl‐ currents in single internally perfused mouse pancreatic acinar cells. With minimal intracellular Ca2+ buffering we found that low concentrations of both ACh (50 nM) and CCK (10 pM) evoked repetitive short‐lasting Ca2+ spikes of the same duration and frequency, but the probability of a spike being followed by a longer and larger Ca2+ wave was low for ACh and high for CCK. The probability that the receptor‐evoked shortlasting Ca2+ spikes would initiate more substantial Ca2+ waves was dramatically increased by intracellular perfusion with solutions containing high concentrations of the mobile low affinity Ca2+ buffers citrate (10–40 mM) or ATP (10–20 mM). The different Ca2+ oscillation patterns normally induced by ACh and CCK would therefore appear not to be caused by separate mechanisms. We propose that specific receptor‐controlled modulation of Ca2+ signal spreading, either by regulation of Ca2+ uptake into organelles and/or cellular Ca2+ extrusion, or by changing the sensitivity of the Ca2(+)‐induced Ca2+ release mechanism, can be mimicked experimentally by different degrees of cytosolic Ca2+ buffering and can account for the various cytosolic Ca2+ spike patterns.