Mitochondrial matrix pH controls oxidative phosphorylation and metabolism-secretion coupling in INS-1E clonal beta cells.
Glucose-evoked mitochondrial signals augment ATP synthesis in the pancreatic β cell. This activation of energy metabolism increases the cytosolic ATP/ADP ratio, which stimulates plasma membrane electrical activity and insulin granule exocytosis. We have recently demonstrated that matrix pH increases during nutrient stimulation of the pancreatic β cell. Here, we have tested whether mitochondrial matrix pH controls oxidative phosphorylation and metabolism-secretion coupling in the rat β-cell line INS-1E. Acidification of the mitochondrial matrix pH by nigericin blunted nutrient-dependent respiratory and ATP responses (continuously monitored in intact cells). Using electrophysiology and single cell imaging, we find that the associated defects in energy metabolism suppress glucose-stimulated plasma membrane electrical activity and cytosolic calcium transients. The same parameters were unaffected after direct stimulation of electrical activity with tolbutamide, which bypasses mitochondrial function. Furthermore, lowered matrix pH strongly inhibited sustained, but not first-phase, insulin secretion. Our results demonstrate that the matrix pH exerts a control function on oxidative phosphorylation in intact cells and that this mode of regulation is of physiological relevance for the generation of downstream signals leading to insulin granule exocytosis. We propose that matrix pH serves a novel signaling role in sustained cell activation.
Akhmedov
Dmitry
D
Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland.
Braun
Matthias
M
Mataki
Chikage
C
Park
Kyu-Sang
KS
Pozzan
Tullio
T
Schoonjans
Kristina
K
Rorsman
Patrik
P
Wollheim
Claes B
CB
Wiederkehr
Andreas
A
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D006367:HeLa Cells; D056945:Hep G2 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D007476:Ionophores / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism*; D009550:Nigericin / Q000494:pharmacology; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects
D007476:Ionophores; D000255:Adenosine Triphosphate; D005947:Glucose; D009550:Nigericin