Functional characterization of hyperpolarization-activated cyclic nucleotide-gated channels in rat pancreatic beta cells.
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels regulate pacemaker activity in some cardiac cells and neurons. In the present study, we have identified the presence of HCN channels in pancreatic beta-cells. We then examined the functional characterization of these channels in beta-cells via modulating HCN channel activity genetically and pharmacologically. Voltage-clamp experiments showed that over-expression of HCN2 in rat beta-cells significantly increased HCN current (I(h)), whereas expression of dominant-negative HCN2 (HCN2-AYA) completely suppressed endogenous I(h). Compared to control beta-cells, over-expression of I(h) increased insulin secretion at 2.8 mmol/l glucose. However, suppression of I(h) did not affect insulin secretion at both 2.8 and 11.1 mmol/l glucose. Current-clamp measurements revealed that HCN2 over-expression significantly reduced beta-cell membrane input resistance (R(in)), and resulted in a less-hyperpolarizing membrane response to the currents injected into the cell. Conversely, dominant negative HCN2-AYA expression led to a substantial increase of R(in), which was associated with a more hyperpolarizing membrane response to the currents injected. Remarkably, under low extracellular potassium conditions (2.5 mmol/l K(+)), suppression of I(h) resulted in increased membrane hyperpolarization and decreased insulin secretion. We conclude that I(h) in beta-cells possess the potential to modulate beta-cell membrane potential and insulin secretion under hypokalemic conditions.
Zhang
Yi
Y
Department of Physiology, University of Toronto, Room 7310, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8. zany.zhang@utoronto.ca
Liu
Yunfeng
Y
Qu
Jihong
J
Hardy
Alexandre
A
Zhang
Nina
N
Diao
Jingyu
J
Strijbos
Paul J
PJ
Tsushima
Robert
R
Robinson
Richard B
RB
Gaisano
Herbert Y
HY
Wang
Qinghua
Q
Wheeler
Michael B
MB
D000818:Animals; D002478:Cells, Cultured; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000378:metabolism*; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D015640:Ion Channel Gating; D008297:Male; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D011189:Potassium Chloride; D051381:Rats; D017208:Rats, Wistar
D054815:Cyclic Nucleotide-Gated Cation Channels; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007328:Insulin; D015221:Potassium Channels; D011189:Potassium Chloride