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Suppressing Na+ influx induces an increase in intracellular ATP concentration in mouse pancreatic beta-cells
1Department of Physiology, Shiga University of Medical Science, Ohtsu, Japan.
Abstract:
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.
Insights
Suppressing sodium (Na+) influx closes ATP-sensitive potassium (K(ATP)) channels in pancreatic beta-cells. This leads to increased intracellular ATP levels, likely by reducing Na+/K+-pump activity.
Area of Science:
- Cellular physiology
- Ion channel function
- Metabolic regulation
Background:
- ATP-sensitive potassium (K(ATP)) channels are crucial in pancreatic beta-cells for regulating insulin secretion.
- Sodium (Na+) ions play a significant role in cellular processes, but their specific impact on K(ATP) channels and ATP levels requires further elucidation.
Purpose of the Study:
- To investigate the effects of modulating Na+ influx on K(ATP) channel activity.
- To determine the impact of altered Na+ levels on intracellular ATP concentration in pancreatic beta-cells.
Main Methods:
- Studied K(ATP) channel activity in mouse pancreatic beta-cells under varying extracellular Na+ concentrations.
- Utilized amiloride and monensin to manipulate Na+/H+-counter transporter and Na+/H+ antiporter activity.
- Measured intracellular ATP concentrations in isolated islets.
- Monitored reduced pyridine nucleotide levels using fluorescence.
Main Results:
- Lowering extracellular Na+ or adding amiloride inhibited K(ATP) channel activity.
- Mannoheptulose reversed amiloride-induced inhibition; monensin increased channel activity.
- Incubation with amiloride or low Na+ solution significantly increased intracellular ATP levels.
- Reduced Na+ influx and Na+/K+-pump inhibition transiently increased reduced pyridine nucleotide.
Conclusions:
- Decreased Na+ influx leads to K(ATP) channel closure in pancreatic beta-cells.
- Reduced Na+ influx elevates intracellular ATP concentration, potentially by decreasing Na+/K+-pump energy consumption.