Characterization of voltage-dependent sodium and calcium channels in mouse pancreatic A- and B-cells.
Insulin and glucagon are the major hormones of the islets of Langerhans that are stored and released from the B- and A-cells, respectively. Both hormones are secreted when the intracellular cytosolic Ca2+ concentration ([Ca2+]i) increases. The [Ca2+]i is modulated by mutual inhibition and activation of different voltage-gated ion channels. The precise interplay of these ion channels in either glucagon or insulin release is unknown, owing in part to the difficulties in distinguishing A- from B-cells in electrophysiological experiments. We have established a single-cell RT-PCR method to identify A- and B-cells from the mouse. A combination of PCR, RT-PCR, electrophysiology and pharmacology enabled us to characterize the different sodium and calcium channels in mouse islet cells. In both A- and B-cells, 60% of the inward calcium current (I(Ca)) is carried by L-type calcium channels. In B-cells, the predominant calcium channel is Ca(v)1.2, whereas Ca(v)1.2 and Ca(v)1.3 were identified in A-cells. These results were confirmed by using mice carrying A- or B-cell-specific inactivation of the Ca(v)1.2 gene. In B-cells, the remaining I(Ca) flows in equal amounts through Ca(v)2.1, Ca(v)2.2 and Ca(v)2.3. In A-cells, 30 and 15% of I(Ca) is due to Ca(v)2.3 and Ca(v)2.1 activity, respectively, whereas Ca(v)2.2 current was not found in these cells. Low-voltage-activated T-type calcium channels could not be identified in A- and B-cells. Instead, two TTX-sensitive sodium currents were found: an early inactivating and a residual current. The residual current was only recovered in a subpopulation of B-cells. A putative genetic background for these currents is Na(v)1.7.
Vignali
Sheila
S
Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Strasse 29, D-80802 München, Germany.
Leiss
Veronika
V
Karl
Rosi
R
Hofmann
Franz
F
Welling
Andrea
A
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D002478:Cells, Cultured; D050416:Glucagon-Secreting Cells / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D015222:Sodium Channels / Q000378:metabolism*; D014018:Tissue Distribution
D015220:Calcium Channels; D015222:Sodium Channels