Overexpression of the Na/Ca Exchanger Shapes Stimulus-Induced Cytosolic Ca2+ Oscillations in Insulin-Producing BRIN-BD11 Cells

  1. Françoise Van Eylen1,
  2. Oscar Diaz Horta1,
  3. Aurore Barez1,
  4. Adama Kamagate1,
  5. Peter R. Flatt2,
  6. Regina Macianskiene3,
  7. Kanigula Mubagwa3 and
  8. André Herchuelz1
  1. 1Laboratory of Pharmacology, Brussels University School of Medicine, Brussels, Belgium
  2. 2School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland, U.K.
  3. 3Centre of Experimental Surgery and Anesthesiology, University of Leuven, Leuven, Belgium

    Abstract

    In response to glucose, mouse β-cells display slow oscillations of the membrane potential and cytosolic free Ca2+ concentration ([Ca2+]i), whereas rat β-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 [Ca2+]i oscillations in pancreatic β-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 β-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 [Ca2+]i on membrane depolarization as well as a more rapid decrease of [Ca2+]i on membrane repolarization. In response to glucose and tolbutamide, control BRIN cells showed large amplitude [Ca2+]i oscillations. In contrast, overexpressing cells showed a staircase increase in [Ca2+]i without such large oscillations. Diazoxide-induced membrane hyperpolarization restored large amplitude [Ca2+]i oscillations in overexpressing cells. The present data confirm that Na/Ca exchange plays a significant role in the rat β-cell [Ca2+]i homeostasis, the exchanger being a versatile system allowing both Ca2+ entry and outflow. Our data suggest that the current generated by the exchanger shapes stimulus-induced membrane potential and [Ca2+]i oscillations in insulin-secreting cells, with the difference in electrical activity and [Ca2+]i behavior seen in mouse and rat β-cells resulting in part from a difference in Na/Ca exchange activity between these two cells.

    Footnotes

    • Address correspondence and reprint requests to André Herchuelz, Laboratoire de Pharmacodynamie et de Thérapeutique, Université Libre de Bruxelles, Faculté de Médecine, Route de Lennik, 808-Bâtiment GE, B-1070 Bruxelles, Belgium. E-mail: herchu{at}ulb.ac.be.

      Received for publication 13 November 2000 and accepted in revised form 26 October 2001.

      [Ca2+]i, cytosolic free Ca2+ concentration; ICa, Ca2+ current; NCX, Na/Ca exchanger; TBS, Tris-buffered saline.

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