Otilonium bromide inhibits calcium entry through L-type calcium channels in human intestinal smooth muscle
P R Strege1, S Evangelista, G L Lyford
1Enteric NeuroScience Program, Mayo Clinic, Rochester, MN 55905, USA.
Abstract:
Otilonium bromide (OB) is used as an intestinal antispasmodic. The mechanism of action of OB is not completely understood. As Ca(2+) entry into intestinal smooth muscle is required to trigger contractile activity, our hypothesis was that OB blocked Ca(2+) entry through L-type Ca(2+) channels. Our aim was to determine the effects of OB on Ca(2+), Na(+) and K(+) ion channels in human jejunal circular smooth muscle cells and on L-type Ca(2+) channels expressed heterologously in HEK293 cells. Whole cell currents were recorded using standard patch clamp techniques. Otilonium bromide (0.09-9 micromol L(-1)) was used as this reproduced clinical intracellular concentrations. In human circular smooth muscle cells, OB inhibited L-type Ca(2+) current by 25% at 0.9 micromol L(-1) and 90% at 9 micromol L(-1). Otilonium bromide had no effect on Na(+) or K(+) currents. In HEK293 cells, 1 micromol L(-1) OB significantly inhibited the expressed L-type Ca(2+) channels. Truncation of the alpha(1C) subunit C and N termini did not block the inhibitory effects of OB. Otilonium bromide inhibited Ca(2+) entry through L-type Ca(2+) at concentrations similar to intestinal tissue levels. This effect may underlie the observed muscle relaxant effects of the drug.
Insights
Otilonium bromide (OB) effectively inhibits L-type calcium channels in human intestinal smooth muscle cells. This action, observed at clinical concentrations, likely explains OB's antispasmodic effects by blocking calcium entry.
Area of Science:
- Pharmacology
- Cell Physiology
- Gastroenterology
Background:
- Otilonium bromide (OB) is a clinically used intestinal antispasmodic.
- Its precise mechanism of action remains incompletely understood.
- Calcium ion (Ca2+) influx is critical for intestinal smooth muscle contraction.
Purpose of the Study:
- To investigate the effects of OB on Ca2+, sodium (Na+), and potassium (K+) ion channels.
- To determine if OB specifically targets L-type Ca2+ channels in human jejunal smooth muscle.
- To validate findings using heterologously expressed L-type Ca2+ channels.
Main Methods:
- Patch clamp electrophysiology was employed to record whole-cell currents.
- Experiments were conducted on human jejunal circular smooth muscle cells.
- L-type Ca2+ channels expressed in HEK293 cells were also studied.
Main Results:
- Otilonium bromide significantly inhibited L-type Ca2+ currents in human smooth muscle cells in a dose-dependent manner (25% at 0.9 µmol/L, 90% at 9 µmol/L).
- OB demonstrated no significant effect on Na+ or K+ currents in these cells.
- In HEK293 cells, 1 µmol/L OB markedly inhibited expressed L-type Ca2+ channels, independent of specific subunit termini.
Conclusions:
- Otilonium bromide inhibits Ca2+ influx through L-type Ca2+ channels at concentrations relevant to clinical intestinal tissue levels.
- This inhibition of Ca2+ channels is a likely mechanism underlying the muscle relaxant and antispasmodic properties of otilonium bromide.
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