Integrating cytosolic calcium signals into mitochondrial metabolic responses.
Stimulation of hepatocytes with vasopressin evokes increases in cytosolic free Ca2+ ([Ca2+]c) that are relayed into the mitochondria, where the resulting mitochondrial Ca2+ ([Ca2+]m) increase regulates intramitochondrial Ca2+-sensitive targets. To understand how mitochondria integrate the [Ca2+]c signals into a final metabolic response, we stimulated hepatocytes with high vasopressin doses that generate a sustained increase in [Ca2+]c. This elicited a synchronous, single spike of [Ca2+]m and consequent NAD(P)H formation, which could be related to changes in the activity state of pyruvate dehydrogenase (PDH) measured in parallel. The vasopressin-induced [Ca2+]m spike evoked a transient increase in NAD(P)H that persisted longer than the [Ca2+]m increase. In contrast, PDH activity increased biphasically, with an initial rapid phase accompanying the rise in [Ca2+]m, followed by a sustained secondary activation phase associated with a decline in cellular ATP. The decline of NAD(P)H in the face of elevated PDH activity occurred as a result of respiratory chain activation, which was also manifest in a calcium-dependent increase in the membrane potential and pH gradient components of the proton motive force (PMF). This is the first direct demonstration that Ca2+-mobilizing hormones increase the PMF in intact cells. Thus, Ca2+ plays an important role in signal transduction from cytosol to mitochondria, with a single [Ca2+]m spike evoking a complex series of changes to activate mitochondrial oxidative metabolism.
Robb-Gaspers
L D
LD
Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
Burnett
P
P
Rutter
G A
GA
Denton
R M
RM
Rizzuto
R
R
Thomas
A P
AP
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D020013:Calcium Signaling; D003600:Cytosol / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D018892:Proton-Motive Force; D011768:Pyruvate Dehydrogenase Complex; D051381:Rats; D017207:Rats, Sprague-Dawley; D014667:Vasopressins / Q000494:pharmacology*
D005227:Fatty Acids; D011768:Pyruvate Dehydrogenase Complex; D014667:Vasopressins; D009249:NADP; D000255:Adenosine Triphosphate