A change in the intracellular Ca(2+) ([Ca(2+)](i)) level induced by hypoxia was detected in rat adrenal slices by use of fura-2/AM. After hypoxic stress, an increase in [Ca(2+)](i) was observed only in the adrenal medulla. This increase was inhibited by nifedipine, but not modified by the cholinergic receptor blockers. The hypoxia-induced increase in [Ca(2+)](i) was observed in all postnatal developmental stages to a similar extent, whereas the nicotine and high K(+) sensitivities increased along with postnatal development. A 10 nM ryanodine enhanced the hypoxia-induced [Ca(2+)](i) increase in adult but not in neonatal rat slices. These results suggest the existence of an oxygen-sensing mechanism in adult rat adrenals even after sympathetic innervation. Hypoxic responses seemed to be similar both in neonate and in adult rat adrenals and were triggered by the influx of Ca(2+) via L-type voltage-sensitive Ca(2+) channels. However, the sustained [Ca(2+)](i) increase caused by hypoxia might depend on postnatal development and be triggered by Ca(2+)-induced Ca(2+) release (CICR).
Copyright 2001 Academic Press.