BK channels affect glucose homeostasis and cell viability of murine pancreatic beta cells.
OBJECTIVE
Evidence is accumulating that Ca(2+)-regulated K(+) (K(Ca)) channels are important for beta cell function. We used BK channel knockout (BK-KO) mice to examine the role of these K(Ca) channels for glucose homeostasis, beta cell function and viability.


METHODS
Glucose and insulin tolerance were tested with male wild-type and BK-KO mice. BK channels were detected by single-cell RT-PCR, cytosolic Ca(2+) concentration ([Ca(2+)](c)) by fura-2 fluorescence, and insulin secretion by radioimmunoassay. Electrophysiology was performed with the patch-clamp technique. Apoptosis was detected via caspase 3 or TUNEL assay.


RESULTS
BK channels were expressed in murine pancreatic beta cells. BK-KO mice were normoglycaemic but displayed markedly impaired glucose tolerance. Genetic or pharmacological deletion of the BK channel reduced glucose-induced insulin secretion from isolated islets. BK-KO and BK channel inhibition (with iberiotoxin, 100 nmol/l) broadened action potentials and abolished the after-hyperpolarisation in glucose-stimulated beta cells. However, BK-KO did not affect action potential frequency, the plateau potential at which action potentials start or glucose-induced elevation of [Ca(2+)](c). BK-KO had no direct influence on exocytosis. Importantly, in BK-KO islet cells the fraction of apoptotic cells and the rate of cell death induced by oxidative stress (H(2)O(2), 10-100 μmol/l) were significantly increased compared with wild-type controls. Similar effects were obtained with iberiotoxin. Determination of H(2)O(2)-induced K(+) currents revealed that BK channels contribute to the hyperpolarising K(+) current activated under conditions of oxidative stress.


CONCLUSIONS
Ablation or inhibition of BK channels impairs glucose homeostasis and insulin secretion by interfering with beta cell stimulus-secretion coupling. In addition, BK channels are part of a defence mechanism against apoptosis and oxidative stress.
Düfer
M
M
Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany.
Neye
Y
Y
Hörth
K
K
Krippeit-Drews
P
P
Hennige
A
A
Widmer
H
H
McClafferty
H
H
Shipston
M J
MJ
Häring
H-U
HU
Ruth
P
P
Drews
G
G
D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D002470:Cell Survival / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D004594:Electrophysiology; D005947:Glucose / Q000378:metabolism*; D006706:Homeostasis; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D016133:Polymerase Chain Reaction; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*
D015221:Potassium Channels; D005947:Glucose