INTRACELLULAR ADP-RIBOSE INHIBITS ATP-SENSITIVE K+ CHANNELS IN RAT VENTRICULAR MYOCYTES

Cyclic ADP-ribose (cADPR), an NAD metabolite, has been shown to be a m essenger for Ca2+ mobilization from intracellular Ca2+ stores. However , the physiological role of ADP-ribose (ADPR), another metabolite of N AD, is not known. We examined the effects of cADPR and ADPR on the ATP -sensitive K+ channel (K-ATP) activity in rat ventricular myocytes by use of the inside-out patch-clamp configuration. ADPR, but not cADPR, inhibited the channel activity at micromolar range with an inhibitor c onstant (K-i) of 38.4 mu M. The Kill coefficient was 0.9. ATP inhibite d the K+ channel with a K-i of 77.8 mu M, and the Hill coefficient was 1.8. Single-channel conductance was not affected by ADPR. These findi ngs strongly suggest that ADPR may act as a regulator of K-ATP channel activity.