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Hyperpolarization-activated cyclic nucleotide-gated channels in pancreatic beta-cells
Wasim El-Kholy1, Patrick E MacDonald, Jocelyn Manning Fox
1Department of Medicine, University of Toronto, Toronto, Canada M5S 1A8.
Molecular Endocrinology (Baltimore, Md.)
|December 13, 2006
Summary
Scientists discovered hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels in pancreatic beta-cells, mediating a novel beta-Ih current. These channels, crucial for pacemaker activity, were functional but did not impact insulin secretion.
Area of Science:
- Cellular Electrophysiology
- Ion Channel Biology
- Endocrinology
Background:
- Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels generate pacemaker currents (Ih or If) in excitable cells.
- These channels are critical for rhythmic electrical activity in cardiac and neuronal tissues.
Purpose of the Study:
- To investigate the presence and function of HCN channels in pancreatic beta-cells.
- To characterize the biophysical and pharmacological properties of the identified beta-Ih current.
Main Methods:
- RT-PCR and quantitative PCR to detect HCN transcripts in rat islets and MIN6 cells.
- Electrophysiological recordings to analyze the beta-Ih current.
- Pharmacological and genetic manipulations (cAMP stimulation, siRNA, dominant-negative channels) to assess channel function.
Main Results:
- HCN1-4 transcripts were detected in pancreatic beta-cells.
- A hyperpolarization-activated time-dependent cationic current, beta-Ih, was identified with properties similar to cardiac/neuronal HCN currents.
- cAMP stimulation shifted activation potential, while siHCN2b or HCN1-AAA inhibited beta-Ih.
- However, beta-Ih inhibition did not affect glucose-stimulated insulin secretion or membrane potential.
Conclusions:
- This study provides the first evidence for functional expression of HCN channels in pancreatic beta-cells.
- The identified beta-Ih current is modulated by cAMP and dependent on HCN channels, particularly HCN2.
- Despite functional expression, HCN channels do not appear to play a significant role in regulating insulin secretion or membrane potential in these cells.
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