ATP-sensitive K+ transport in adrenal chromaffin granules

In the present study the influx of Rb-86(+), a K+ analogue, was studied in mitochondria, microsomes and chromaffin granules prepared from adrenal glan d medulla. The most active electrogenic Rb-86(+) transport was found in the membrane fraction identified as chromaffin granules by marker enzyme estim ation. The transport was found to be sensitive to ATP, ATP gammaS, ADP and to the triazine dyes, but not to AMP and cAMP. The inhibition induced by AT P was observed in the absence of externally added Mg2+, suggesting that a f ree nucleotide, rather than the ATP-Mg complex, was required for inhibition . Furthermore, the Rb-86(+) influx was found to be inhibited by Mg2+ alone, but not by Ca2+ and antidiabetic sulfonylureas. The Rb-86(+) influx was no t Stimulated by potassium channel openers. In conclusion, our results indic ate that an electrogenic, ATP sensitive potassium transport system operates in the chromaffin granule membrane.