Evidence for decline in intracellular calcium buffering in adrenergic nerves of aged rats

Age-related alterations in neuronal intracellular calcium regulation and neurotransmitter release have been widely reported. We have investigated the impact of age on neurotransmitter release and intracellular calcium buffering in adrenergic nerve endings of the isolated rat tail artery and on intracellular calcium in acutely dissociated cells from the superior cervical ganglion. Advancing age, from 6 to 27 months, resulted in significantly increased stimulation-evoked norepinephrine release from the isolated rat tail artery, an effect which persisted when neuronal and extraneuronal uptake were blocked with cocaine and deoxycorticosterone and presynaptic alpha adrenergic receptors were blocked with idazoxan. Alterations in extracellular calcium had significant effect on stimulation-evoked norepinephrine release, but these were much more marked in old, compared to young, arteries. Blockade of mitochondrial calcium accumulation with dinitrophenol had no significant effect on stimulation-evoked norepinephrine release from 6-month-old arteries, but in 20-month-old arteries, treatment with dinitrophenol resulted in a substantial increase in stimulation-evoked norepinephrine release. However, when extracellular calcium was increased to 5 mM in 6 month-old-arteries, then addition of dinitrophenol resulted in an increase in stimulation-evoked norepinephrine release. Measurement of intracellular calcium in acutely dissociated superior cervical ganglion cells using fura-2 revealed substantial age-related differences. Peak calcium transients in 20-month-old ganglion cells depolarized with 68 mM K⁺ were substantially higher than in 6-month-old cells. Together these findings support the hypothesis that in adrenergic nerves advancing age results in a disruption of intracellular calcium buffering leading to higher levels of intracellular calcium and increased transmitter release.