Background: Bamboo shoot has been used as a treatment for epilepsy in traditional
Chinese medicine for generations to treat neuronal disorders such as convulsive, dizziness
and headaches. 4-hydroxybenzoic acid (4-hba) is a non-flavonoid phenol found abundantly in
Dendrocalamus asper shoots (bamboo), fruits (strawberries and apples) and flowers. Kv1.4 is
a rapidly inactivating
Shaker-related member of the voltage-gated potassium channels with two
inactivation mechanisms; the fast N-type and slow C-type. It plays vital roles in repolarisation,
hyperpolarisation and signaling the restoration of resting membrane potential through the
regulation of the movement of K+ across the cellular membrane.
Methods: Chemical compounds from
Dendrocalamus asper bamboo shoots were
purified and identified as major palmitic acids mixed with other minor fatty acids, palmitic
acid, 4-hydroxybenzaldehyde, lauric acid, 4-hydroxybenzoic acid and cholest-4-ene-3-one. The
response of synthetic 4-hydroxybenzoic acid was tested on Kv1.4 potassium channel which was
injected into viable oocytes that was extracted from
Xenopus laevis
. The current were detected by
the two-microelectrode voltage clamp, holding potential starting from −80 mV with 20 mV step-up
until +80 mV. Readings of treatments with 0.1% DMSO, 4-hba concentrations and K channel
blockers were taken at +60 mV. The ratio of tail/peak amplitude is the index of the activity of the
Kv1.4 channels with
n ≥ 6 (number of oocytes tested). The decreases of the ratios of five different
concentrations (1 μM, 10 μM, 100 μM, 1 mM and 2.5 mM) were compared with 0.1% DMSO as the
control.
Results: All concentration showed statistically significant results with
P < 0.05 except
for 100 μM. The normalised current of the 4-hba concentrations were compared with potassium
channel blockers (TEA and 4-AP) and all groups showed statistically significant results. This study
also showed that time taken for each concentration to affect Kv1.4 does not play any significant
roles.
Conclusion: 4-hydroxybenzoic acid was found to be able to enhance the inactivation of
Kv1.4 by lowering the membrane potential so that the abnormal neuronal firing can be inhibited.
With IC
50 slightly higher than 10 μM, increasing concentrations (100 μM, 1 mM and 2.5 mM) had
shown to exhibit toxicity effects. The best concentration from this study is 10 μM with Hill slope of
0.1799.
