Repetitive mitochondrial Ca2+ signals synchronize with cytosolic Ca2+ oscillations in the pancreatic beta-cell line, MIN6.
We examined the relationship between cytosolic Ca2+ concentration ([Ca2+]c) and mitochondrial matrix Ca2+ concentration ([Ca2+]m) in the pancreatic beta-cell line, MIN6. [Ca2+]c was monitored in a single or a group (30 cells) of fura-2-loaded MIN6 cells, and [Ca2+]m was measured in a group (1 x 10[6] cells) of MIN6 cells stably transfected with aequorin targeted at the mitochondria. Exogenous ATP (0.25 mmol/l) produced a single transient increase in [Ca2+]c whereas 22 mmol/l KCl produced a sustained plateau increase. ATP and KCl evoked transient increases in [Ca2+]m but with distinct time courses of [Ca2+]m decline: the [Ca2+]m increase induced by ATP decreased more rapidly than that induced by KCl. Nitrendipine (3 micromol/l), a blocker of L-type Ca2+ channels, inhibited both [Ca2+]c and [Ca2+]m signals in response to KCl and tolbutamide, but not those to ATP. Peak levels of [Ca2+]m increase (around 2 micromol/ l) exceeded those of [Ca2+]c increase (around 500 nmol/l). A rise in glucose concentration from 3 to 30 mmol/l induced oscillations of [Ca2+]c that overlay the sustained increases in [Ca2+]c in single cells. An oscillatory increase in [Ca2+]m was similarly observed in response to glucose. Addition of 10 mmol/l 2-ketoisocaproic acid at 20 mmol/l glucose further increased the plateau level of [Ca2+]c and the frequency of [Ca2+]c oscillations, which were correlated with a further increase in [Ca2+]m. In response to pulsatile exposure to KCl, [Ca2+]c and [Ca2+]m increased synchronously. These data suggest that an oscillatory increase in [Ca2+]m in beta cells, the signal which is thought to be necessary for continuous stimulation of mitochondrial metabolism, is produced synchronously with the [Ca2+]c oscillations.
Nakazaki
M
M
First Department of Internal Medicine, Faculty of Medicine, Kagoshima University, Japan.
Ishihara
H
H
Kakei
M
M
Inukai
K
K
Asano
T
T
Miyazaki
J I
JI
Tanaka
H
H
Kikuchi
M
M
Yada
T
T
Oka
Y
Y
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000331:Aequorin / Q000032:analysis / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000378:metabolism; D002460:Cell Line; D002614:Chelating Agents / Q000032:analysis; D003600:Cytosol / Q000187:drug effects / Q000502:physiology*; D015342:DNA Probes / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000032:analysis; D016257:Fura-2 / Q000032:analysis; D005947:Glucose / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007515:Islets of Langerhans / Q000737:chemistry / Q000166:cytology / Q000502:physiology; D008928:Mitochondria / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D011189:Potassium Chloride / Q000008:administration & dosage / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D014044:Tolbutamide / Q000494:pharmacology
D015220:Calcium Channels; D002614:Chelating Agents; D015342:DNA Probes; D005456:Fluorescent Dyes; D007004:Hypoglycemic Agents; D000331:Aequorin; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D014044:Tolbutamide; D005947:Glucose; D002118:Calcium; D016257:Fura-2