Diosgenin, a Plant-Derived Sapogenin, Stimulates Ca²⁺-Activated K⁺ Current in Human Cortical HCN-1A Neuronal Cells

Abstract

The effects of diosgenin (3β-hydroxy-5-spirostene), a plant-derived sapogenin, on ion currents in human cortical neurons (HCN-1A) were investigated. In the whole-cell configuration, diosgenin (0.3 - 30 μM) increased the amplitude of K⁺ outward current (I _K). Diosgenin-stimulated I _K was sensitive to inhibition by paxilline (1 μM), but not by apamin (200 nM) or glibenclamide (10 μM). In the cell-attached configuration, diosgenin applied to the bath increased the activity of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels without altering single-channel conductance. Diosgenin enhanced BK_Ca-channel activity with an EC₅₀ value of 25 μM. However, in inside-out patches, diosgenin applied to the intracellular surface had no effect on BK_Ca-channel activity, while cilostazol or caffeic acid phenethyl ester increased it. As shown with the aid of intracellular Ca²⁺ measurements, diosgenin elevated intracellular Ca²⁺ in HCN-1A cells. Western blotting also revealed the presence of the α-subunit of BK_Ca channels in these cells. The sustained stimulation of I _K arises primarily from the diosgenin-induced Ca²⁺ influx across the cell membrane. The effect of diosgenin on these channels may affect the functional activity of cortical neurons.

Abbreviations

I _K:K⁺ outward current

I _K(Ca):Ca²⁺-activated K⁺ current

BK_Ca channel:Large-conductance Ca²⁺-activated K⁺ channel

CAPE:caffeic acid phenethyl ester

[Ca²⁺]_i:intracellular Ca²⁺ concentration

I/V relationship:current/voltage relationship

K_ATP channel:ATP-sensitive K⁺ channel

K_Ca channel:Ca²⁺-activated K⁺ channel

Key words

Diosgenin - Ca²⁺-activated K⁺ currents - HCN-1A cells

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