Expression and Function of Pancreatic β-Cell Delayed Rectifier K+ Channels

• Published in: The Journal of biological chemistry 1996-12, Vol.271 (50), p.32241
• Main Authors: Michael Wm. Roe, Jennings F. Worley III, Anshu A. Mittal, Andrey Kuznetsov, Sarmila DasGupta, Robert J. Mertz, Sam M. Witherspoon III, Nathaniel Blair, Mary E. Lancaster, Margaret S. McIntyre, W. Ronald Shehee, Iain D. Dukes, Louis H. Philipson
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.271.50.32241

Voltage-dependent delayed rectifier K + channels regulate aspects of both stimulus-secretion and excitation-contraction coupling, but assigning specific roles to these channels has proved problematic. Using transgenically derived insulinoma cells (βTC3-neo) and β-cells purified from rodent pancreatic islets of Langerhans, we studied the expression and role of delayed rectifiers in glucose-stimulated insulin secretion. Using reverse-transcription polymerase chain reaction methods to amplify all known candidate delayed rectifier transcripts, the expression of the K + channel gene Kv2.1 in βTC3-neo insulinoma cells and purified rodent pancreatic β-cells was detected and confirmed by immunoblotting in the insulinoma cells. βTC3-neo cells were also found to express a related K + channel, Kv3.2. Whole-cell patch clamp demonstrated the presence of delayed rectifier K + currents inhibited by tetraethylammonium (TEA) and 4-aminopyridine, with similar K d values to that of Kv2.1, correlating delayed rectifier gene expression with the K + currents. The effect of these blockers on intracellular Ca 2+ concentration ([Ca 2+ ] i ) was studied with fura-2 microspectrofluorimetry and imaging techniques. In the absence of glucose, exposure to TEA (1-20 mM) had minimal effects on βTC3-neo or rodent islet [Ca 2+ ] i , but in the presence of glucose, TEA activated large amplitude [Ca 2+ ] i oscillations. In the insulinoma cells the TEA-induced [Ca 2+ ] i oscillations were driven by synchronous oscillations in membrane potential, resulting in a 4-fold potentiation of insulin secretion. Activation of specific delayed rectifier K + channels can therefore suppress stimulus-secretion coupling by damping oscillations in membrane potential and [Ca 2+ ] i and thereby regulate secretion. These studies implicate previously uncharacterized β-cell delayed rectifier K + channels in the regulation of membrane repolarization, [Ca 2+ ] i , and insulin secretion.