Suppressing Na+ influx induces an increase in intracellular ATP concentration in mouse pancreatic beta-cells.

The effects of suppressing Na+ influx on the activity of ATP-sensitive K+ channels (K(ATP) channel) and intracellular ATP concentration in mouse pancreatic beta-cells were studied. Lowering extracellular Na+ concentration brought about a closing of K(ATP) channels. The activity of K(ATP) channels was markedly inhibited by the addition of amiloride, a blocker of Na+/H+-counter transporter. Mannoheptulose completely eliminated the inhibition otherwise induced by amiloride. Monensin, an electroneutral Na+/H+ antiporter, remarkably increased the activity of K(ATP) channels. Removing extracellular Ca2+ also caused inhibition of the channel activity. ATP measurement experiments using isolated islets revealed that the intracellular ATP concentration of islet cells was significantly increased by incubating either with amiloride or a low Na+ solution. The measurement of fluorescence excited at 360 nm demonstrated that both suppressing Na+ influx and inhibition of Na+/K+-pumps caused a transient increase in the reduced form of pyridine nucleotide. These findings indicate that a decrease in Na+ influx could cause an elevation in intracellular ATP concentration probably through inducing a fall in ATP consumption at the Na+/K+-pump sites.