Abstract

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 β-cells. We then examined the functional characterization of these channels in β-cells via modulating HCN channel activity genetically and pharmacologically. Voltage-clamp experiments showed that over-expression of HCN2 in rat β-cells significantly increased HCN current (I_h), whereas expression of dominant-negative HCN2 (HCN2-AYA) completely suppressed endogenous I_h. Compared to control β-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 β-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 β-cells possess the potential to modulate β-cell membrane potential and insulin secretion under hypokalemic conditions.