ATP-sensitive K+ transport in adrenal chromaffin granules

Abstract

In the present study the influx of 86Rb+, a K+ analogue, was studied in mitochondria, microsomes and chromaffin granules prepared from adrenal gland medulla. The most active electrogenic 86Rb+ transport was found in the membrane fraction identified as chromaffin granules by marker enzyme estimation. The transport was found to be sensitive to ATP, ATP-gamma-S, ADP and to the triazine dyes, but not to AMP and cAMP. The inhibition induced by ATP was observed in the absence of externally added Mg2+, suggesting that a free nucleotide, rather than the ATP-Mg complex, was required for inhibition. Furthermore, the 86Rb+ influx was found to be inhibited by Mg2+ alone, but not by Ca2+ and antidiabetic sulfonylureas. The 86Rb+ influx was not stimulated by potassium channel openers. In conclusion, our results indicate that an electrogenic, ATP-sensitive potassium transport system operates in the chromaffin granule membrane.