Madhu Prasad1, Raj K Goyal. 1. Department of Surgery, Veterans Affairs Medical Centers, West Roxbury, MA 02132, USA.
Abstract
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.
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 taurinemonochloramine 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.