Expression and function of pancreatic beta-cell delayed rectifier K+ channels. Role in stimulus-secretion coupling.
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 (betaTC3-neo) and beta-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 betaTC3-neo insulinoma cells and purified rodent pancreatic beta-cells was detected and confirmed by immunoblotting in the insulinoma cells. betaTC3-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 Kd values to that of Kv2.1, correlating delayed rectifier gene expression with the K+ currents. The effect of these blockers on intracellular Ca2+ concentration ([Ca2+]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 betaTC3-neo or rodent islet [Ca2+]i, but in the presence of glucose, TEA activated large amplitude [Ca2+]i oscillations. In the insulinoma cells the TEA-induced [Ca2+]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 [Ca2+]i and thereby regulate secretion. These studies implicate previously uncharacterized beta-cell delayed rectifier K+ channels in the regulation of membrane repolarization, [Ca2+]i, and insulin secretion.
Roe
M W
MW
Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA. l-philipson@uchicago.edu
Worley
J F
JF
Mittal
A A
AA
Kuznetsov
A
A
DasGupta
S
S
Mertz
R J
RJ
Witherspoon
S M
SM
Blair
N
N
Lancaster
M E
ME
McIntyre
M S
MS
Shehee
W R
WR
Dukes
I D
ID
Philipson
L H
LH
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D051668:Delayed Rectifier Potassium Channels; D005434:Flow Cytometry; D005947:Glucose / Q000378:metabolism; D007515:Islets of Langerhans / Q000737:chemistry*; D008564:Membrane Potentials; D051379:Mice; D008969:Molecular Sequence Data; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D016415:Sequence Alignment; D051669:Shab Potassium Channels; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D051668:Delayed Rectifier Potassium Channels; C496990:Kcnb1 protein, mouse; C496991:Kcnb1 protein, rat; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051669:Shab Potassium Channels; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D005947:Glucose; D002118:Calcium