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Action by Shakuyaku‐kanzo‐to (SKT) and one of its Chemical Components, Glycyrrhetic acid (GA), on Calcium Influx through L‐type Calcium Channel
Author(s) -
Noble Denis,
Sam Cynthia,
Tasaki Kazuyo Maria
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.lb710
Subject(s) - chemistry , calcium , biophysics , potassium , extracellular , voltage dependent calcium channel , fura 2 , calcium channel , skeletal muscle , biochemistry , endocrinology , medicine , biology , cytosol , enzyme , organic chemistry
Our previous work has shown that SKT, a standardized 1:1 combination of root extracts from paeony and licorice, rapidly relaxes smooth muscle within 1–2 mins, and slowly relaxes skeletal muscle within about 30 minutes (Sam, Terrar, Tasaki & Noble, 2015a). We have also shown that increasing extracellular potassium from 5.4 to 10.8 mM is a powerful facilitator of the relaxing action of SKT in skeletal muscle (Sam, Terrar, Noble, Tasaki & Noble, 2015b). Methods To investigate possible molecular mechanisms we recorded calcium influx through the alpha1 pore‐forming subunit of the L‐Type calcium channel expressed in HEK293 cells. Influx was estimated by measuring the difference in Fura‐2 fluorescence before and after activating the channels with high (100 mM) potassium. Patch clamp recordings were done at −80 mV and depolarising pulses were applied from −80 to +40 mV. Pulse duration was between 50 and 200 ms. In some experiments ramps were applied from −100 to +100 mV. Results SKT produced up to 50% inhibition of calcium influx through the pore‐forming subunit of the L‐type calcium channel in HEK cells ( Figure 1). The results also show considerable variability that may be consistent with differing actions of some of the individual chemical components. One of the pure chemical components, GA, however produces a consistent and statistically significant inhibition of calcium influx, which is up to 80% ( Figure 2). Discussion In muscle cells, such inhibitions of calcium influx would be expected to deplete cell calcium and so reduce the phasic contractile response and relax tonic resting tension. Since ICaL plays an immediate role in smooth muscle but only a long term role in skeletal muscle, this would be consistent with our previous observation of different time courses between SKT's actions on smooth and skeletal muscles. There was, however, no statistically significant inhibition of calcium current using controlled voltage patch clamp recording. The action on inhibiting influx could therefore be indirect. Support or Funding Information Acknowledgement: This research is conducted by the University of Oxford Innovative Systems Biology Project Sponsored by Tsumura. We thank TSUMURA & CO for their support.