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Monochloramine selectively inhibits the transient outward potassium current in colonic smooth muscle
1Department of Surgery, Veterans Affairs Medical Centers, West Roxbury, MA 02132, USA.
Background:
During colitis, activated neutrophils elaborate biologically active oxidants into the bowel wall. Colonic contraction, governed by plasma membrane ion channels in smooth muscle cells (SMCs), is markedly abnormal in colitis. The transient outward K(+) current (I(TO)) is an important determinant of electrical excitability in colonic SMCs. The aim of this study was to characterize the effect of the colon-specific oxidant monochloramine (NH(2)Cl) on I(TO) in SMCs of the mouse colon.
Methods:
The effects of NH(2)Cl on I(TO) in freshly isolated single SMCs were examined with the whole cell patch clamp techniques. Cloned K(v)4 currents were measured in Xenopus oocytes with a 2-electrode voltage clamp.
Results:
NH(2)Cl induced rapid, irreversible, and potent (EC(50) = 520 +/- 40 nmol/L) inhibition of I(TO). The cell-impermeant oxidant taurine monochloramine did not affect I(TO). NH(2)Cl did not alter the kinetics of I(TO) activation or inactivation. Voltage-dependent availability of I(TO) was unaffected by NH(2)Cl, as was recovery from inactivation. NH(2)Cl abolished currents that were elicited by cloned K(v)4 channels.
Conclusions:
NH(2)Cl selectively inhibits I(TO) at concentrations within the range that are produced during colitis. Suppression of I(TO) by NH(2)Cl in SMCs occurs by an effect on the channel alpha subunit mediated from within the cytosol. Oxidant-induced changes in ion channel activity in colonic SMCs may contribute to abnormal motility in colitis.
Insights
Monochloramine (NH2Cl), a colon-specific oxidant, potently inhibits the transient outward K+ current (I(TO)) in colonic smooth muscle cells (SMCs). This oxidant-induced suppression of I(TO) may contribute to abnormal colonic motility during colitis.
Area of Science:
- Gastroenterology
- Ion Channel Physiology
- Smooth Muscle Biology
Background:
- Colitis is associated with abnormal colonic contraction due to altered ion channel function in smooth muscle cells (SMCs).
- Neutrophils in colitis release oxidants, impacting the bowel wall.
- The transient outward K+ current (I(TO)) is crucial for colonic SMC electrical excitability.
Purpose of the Study:
- To investigate the effect of the colon-specific oxidant monochloramine (NH2Cl) on I(TO) in mouse colonic SMCs.
Main Methods:
- Whole-cell patch clamp techniques were used to examine NH2Cl's effects on I(TO) in isolated colonic SMCs.
- Two-electrode voltage clamp assessed cloned K(v)4 currents in Xenopus oocytes.
Main Results:
- NH2Cl caused rapid, irreversible, and potent inhibition of I(TO) (EC50 = 520 +/- 40 nmol/L).
- NH2Cl abolished currents mediated by cloned K(v)4 channels.
- The kinetics, activation, inactivation, and voltage-dependent availability of I(TO) were not altered by NH2Cl.
Conclusions:
- NH2Cl selectively inhibits I(TO) at concentrations relevant to colitis.
- The inhibition of I(TO) by NH2Cl in SMCs is mediated by an effect on the channel alpha subunit from the cytosol.
- Oxidant-induced alterations in colonic SMC ion channel activity may play a role in the abnormal motility observed in colitis.