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Effect of Age on K+‐Induced Cytosolic Ca2+ Changes in Rat Cortical Synaptosomes

Abstract: 45Ca2+ uptake and cytosolic Ca2+ Concentrations ([Ca2+]i) were measured in synaptosomes prepared from the cerebral cortex of 3‐, 16‐, and 24‐month‐old male Charles River Wistar rats. Electron‐microscopic examination demonstrated no morphological differences between the synaptosomes prepared from 3‐ and 24‐month‐old rats. The fast phase of Ca2+ uptake was reduced in the 24‐month‐old animals as compared to the 3‐month‐old ones (‐23%. p < 0.001), whereas no difference was found between the 16‐and the 3‐month‐old rats. Age did not modify [Ca2+]i, as measured by the quin 2 technique, both at rest and immediately after depolarization with 50 mM K+. The Ca2+ load following depolarization was cleared in about 13 min in the 3‐month‐old rats. The rate of clearance was significantly slower both in the 16‐ (p <0.01) and in the 24‐month‐old rats (p < 0.0001). The addition of verapamil (60 μM) after depolarization restored [Ca2+]i to resting level in aged rats at the same rate as in young rats. A prolonged Ca2+ influx, therefore, may be responsible for the slower clearance of Ca2+load in aged rats.