Overexpression of the Na/Ca exchanger shapes stimulus-induced cytosolic Ca(2+) oscillations in insulin-producing BRIN-BD11 cells.
In response to glucose, mouse beta-cells display slow oscillations of the membrane potential and cytosolic free Ca(2+) concentration ([Ca(2+)](i)), whereas rat beta-cells display a staircase increase in these parameters. Mouse and rat islet cells differ also by their level of Na/Ca exchanger (NCX) activity. The view that the inward current generated by Na/Ca exchange shapes stimulus-induced electrical activity and [Ca(2+)](i) oscillations in pancreatic beta-cells was examined in insulin-producing BRIN-BD11 cells overexpressing the Na/Ca exchanger. BRIN-BD11 cells were stably transfected with NCX1.7, one of the exchanger isoforms identified in the beta-cell. Overexpression could be assessed at the mRNA and protein level. Appropriate targeting to the plasma membrane could be assessed by microfluorescence and the increase in Na/Ca exchange activity. In response to K(+), overexpressing cells showed a more rapid increase in [Ca(2+)](i) on membrane depolarization as well as a more rapid decrease of [Ca(2+)](i) on membrane repolarization. In response to glucose and tolbutamide, control BRIN cells showed large amplitude [Ca(2+)](i) oscillations. In contrast, overexpressing cells showed a staircase increase in [Ca(2+)](i) without such large oscillations. Diazoxide-induced membrane hyperpolarization restored large amplitude [Ca(2+)](i) oscillations in overexpressing cells. The present data confirm that Na/Ca exchange plays a significant role in the rat beta-cell [Ca(2+)](i) homeostasis, the exchanger being a versatile system allowing both Ca(2+) entry and outflow. Our data suggest that the current generated by the exchanger shapes stimulus-induced membrane potential and [Ca(2+)](i) oscillations in insulin-secreting cells, with the difference in electrical activity and [Ca(2+)](i) behavior seen in mouse and rat beta-cells resulting in part from a difference in Na/Ca exchange activity between these two cells.
Van Eylen
Françoise
F
Laboratory of Pharmacology, Brussels University School of Medicine, Brussels, Belgium.
Horta
Oscar Diaz
OD
Barez
Aurore
A
Kamagate
Adama
A
Flatt
Peter R
PR
Macianskiene
Regina
R
Mubagwa
Kanigula
K
Herchuelz
André
A
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics / Q000502:physiology; D002459:Cell Fusion; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism*; D003981:Diazoxide / Q000494:pharmacology; D004553:Electric Conductivity; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D009991:Oscillometry; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D014044:Tolbutamide / Q000494:pharmacology; D014162:Transfection
D007004:Hypoglycemic Agents; D007328:Insulin; D019831:Sodium-Calcium Exchanger; D014044:Tolbutamide; D005947:Glucose; D003981:Diazoxide; D011188:Potassium; D002118:Calcium