Biophysical and pharmacological properties of the voltage-gated potassium current of human pancreatic β-cells

Voltage-gated potassium (Kv) currents of human pancreatic islet cells were studied by whole-cell patch clamp recording. On average, 75% of the cells tested were identified as β-cells by single cell, post-recording RT-PCR for insulin mRNA. In most cells, the dominant Kv current was a delayed rectifier. The delayed rectifier activated at potentials above - 20 mV and had a V_1/2 for activation of -5.3 mV. Onset of inactivation was slow for a major component (τ = 3.2 s at +20 mV) observed in all cells; a smaller component (τ = 0.30 s) with an amplitude of ∼25% was seen in some cells. Recovery from inactivation had a τ of 2.5 s at -80 mV and steady-state inactivation had a V_1/2 of -39 mV. In 12% of cells (21/182) a low-threshold, transient Kv current (A-current) was present. The A-current activated at membrane potentials above -40 mV, inactivated with a time constant of 18.5 ms at -20 mV, and had a V_1/2 for steady-state inactivation of -52 mV. TEA inhibited total Kv current with an IC₅₀ = 0.54 mM and PAC, a disubstituted cyclohexyl Kv channel inhibitor, inhibited with an IC₅₀ = 0.57 μM. The total Kv current was insensitive to margatoxin (100 nM), agitoxin-2 (50 nM), kaliotoxin (50 nM) and ShK (50 nM). Hanatoxin (100 nM) inhibited total Kv current by 65% at +20 mV. Taken together, these data provide evidence of at least two distinct types of Kv channels in human pancreatic β-cells and suggest that more than one type of Kv channel may be involved in the regulation of glucose-dependent insulin secretion.