Abstract
Adrenal chromaffin cells of adult guinea-pig rapidly secrete catecholamine in response to hypoxia, whereas those of adult rat fail to do. Thus, we explored what was responsible for this difference. Rat chromaffin cells showed a little, if any, secretory response to various mitochondrial inhibitors, whereas guinea-pig chromaffin cells responded markedly to them. The order of rank of the stimulating potency was oligomycin A<CN−<CCCP. This result suggests that the inhibitor-induced secretion may not be due to a change in reactive oxygen species or NADH concentrations. Alternatively, it may be ascribed to a decrease in cellular ATP contents. Thus, this possibility was examined indirectly using the Mg2+ indicator MgGreen. Since the majority of cellular ATP is present as MgATP, a decrease in ATP can be measured as an increase in Mg2+ ions. Application of CCCP resulted in about 25% and 12% increases in MgGreen fluorescence in guinea-pig and rat chromaffin cells, respectively. Similarly, the extent of CN−-induced increase in the fluorescence in the latter was about half of that in the former, suggesting that the extent of ATP hydrolysis in response to mitochondrial inhibitors was larger in guinea-pig than that in rat chromaffin cells. Consistent with this result, a relative expression level of ATP synthase, which may operate in the reverse mode with consumption of ATP in hypoxia, was larger in guinea-pig than that in rat adrenal medulla. The present results raise the possibility that ATP synthase in mitochondria may play an important role for hypoxia detection in adrenal chromaffin cells. [Jpn J Physiol 54 Suppl:S71 (2004)]
