AGE-RELATED-CHANGES IN THE SENSITIVITY OF SYMPATHETIC-NERVES TO ALTERED EXTRACELLULAR CALCIUM IN TAIL ARTERIES OF F344 RATS

There is a significant age-related increase in stimulation evoked nore pinephrine release from adrenergic nerves in tail arteries of F-344 ra ts, that is not accounted for by a change in function of prejunctional alpha 2-adrenergic receptors. To further explore the mechanism of thi s age-related change in transmitter release, we investigated the effec t of altered extracellular calcium. With short stimulation trains the effects of altered extracellular calcium were significantly greater in 20-month-old tail arteries compared to 6 months. At the highest calci um concentration (7.5 mM) when alpha 2-adrenergic receptors were activ e or blocked, there was a significant decline in fractional norepineph rine release only in arteries of 20-month-old animals. With long stimu lation trains the effects of altered extracellular calcium were not as pronounced as with short trains, but the effect of calcium was still significantly greater in 20 month old tail arteries. With alpha 2-adre nergic receptors blocked 6 month tail arteries were insensitive to alt ered calcium while 20-month tail arteries remained sensitive. One expl anation for these findings may be an age-related change in the efficie ncy of intracellular calcium buffering mechanisms leading to greater c alcium transients in the nerves of older animals.