KATP channel activity and slow oscillations in pancreatic beta cells are regulated by mitochondrial ATP production

• Published in: The Journal of physiology Vol. 601; no. 24; pp. 5655 - 5667
• Main Authors: Corradi, Jeremías, Thompson, Benjamin, Fletcher, Patrick A., Bertram, Richard, Sherman, Arthur S., Satin, Leslie S.
• Format: Journal Article
• Language: English
• Published: London Wiley Subscription Services, Inc 01.12.2023
• Subjects: [ATP]/[ADP] ratio; Adenosine diphosphate; Beta cells; Calcium signalling; Channel gating; Glucose; Glucose metabolism; glucose response; insulin secretion; KATP channels; Mathematical models; Mitochondria; Oxidative phosphorylation; Pancreas; pH modulation; Phosphorylation; Protons; Pyruvate kinase; Pyruvic acid
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/JP284982

Pancreatic beta cells secrete insulin in response to plasma glucose. The ATP‐sensitive potassium channel (KATP) links glucose metabolism to islet electrical activity in these cells by responding to increased cytosolic [ATP]/[ADP]. It was recently proposed that pyruvate kinase (PK) in close proximity to beta cell KATP locally produces the ATP that inhibits KATP activity. This proposal was largely based on the observation that applying phosphoenolpyruvate (PEP) and ADP to the cytoplasmic side of excised inside‐out patches inhibited KATP. To test the relative contributions of local vs. mitochondrial ATP production, we recorded KATP activity using mouse beta cells and INS‐1 832/13 cells. In contrast to prior reports, we could not replicate inhibition of KATP activity by PEP + ADP. However, when the pH of the PEP solutions was not corrected for the addition of PEP, strong channel inhibition was observed as a result of the well‐known action of protons to inhibit KATP. In cell‐attached recordings, perifusing either a PK activator or an inhibitor had little or no effect on KATP channel closure by glucose, further suggesting that PK is not an important regulator of KATP. In contrast, addition of mitochondrial inhibitors robustly increased KATP activity. Finally, by measuring the [ATP]/[ADP] responses to imposed calcium oscillations in mouse beta cells, we found that oxidative phosphorylation could raise [ATP]/[ADP] even when ADP was at its nadir during the burst silent phase, in agreement with our mathematical model. These results indicate that ATP produced by mitochondrial oxidative phosphorylation is the primary controller of KATP in pancreatic beta cells. Key points Phosphoenolpyruvate (PEP) plus adenosine diphosphate does not inhibit KATP activity in excised patches. PEP solutions only inhibit KATP activity if the pH is unbalanced. Modulating pyruvate kinase has minimal effects on KATP activity. Mitochondrial inhibition, in contrast, robustly potentiates KATP activity in cell‐attached patches. Although the ADP level falls during the silent phase of calcium oscillations, mitochondria can still produce enough ATP via oxidative phosphorylation to close KATP. Mitochondrial oxidative phosphorylation is therefore the main source of the ATP that inhibits the KATP activity of pancreatic beta cells. figure legend The intracellular mechanisms that control KATP channel activity in insulin‐secreting pancreatic beta cells were investigated. From inside‐out and cell‐attached electrophysiological recordings, we found that KATP activity was not significantly affected by ATP synthesized by pyruvate kinase. However, in intact beta cells perifused with high glucose concentrations, we observed a dramatic increase in KATP channel activity when mitochondrially produced ATP was inhibited by NaN3 or rotenone (two inhibitors of the electron transport chain). These results confirm that the ATP synthesized by oxidative phosphorylation is the main factor responsible for KATP modulation in beta cells. This mechanism was also supported by simulations of the Integrated Oscillator Model for beta cells. The top trace in the figure corresponds to a cell‐attached recording of KATP obtained from mouse beta cells under the indicated conditions.