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Effect of nitric oxide on calcium-activated potassium channels in colonic smooth muscle of rabbits

G Lu1, B Mazet, M G Sarr

  • 1Department of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905, USA.

The American Journal of Physiology
|June 5, 1998
PubMed

Insights

Nitric oxide (NO) activates potassium calcium-activated (KCa) channels in rabbit colon smooth muscle. This process occurs via a cyclic guanosine monophosphate (cGMP) pathway, leading to smooth muscle hyperpolarization.

Area of Science:

  • Physiology
  • Gastroenterology
  • Molecular Biology

Background:

  • Nitric oxide (NO) is known to hyperpolarize intestinal smooth muscle cells.
  • The precise mechanism by which NO influences KCa channels in the colon remains to be fully elucidated.

Purpose of the Study:

  • To determine the mechanism by which nitric oxide (NO) activates KCa channels in circular smooth muscle of the rabbit colon.
  • To investigate the role of cyclic guanosine monophosphate (cGMP) in NO-mediated KCa channel activation.

Main Methods:

  • NADPH-diaphorase staining to identify nerve fibers in rabbit colon transmural biopsies.
  • Whole-cell, on-cell, and excised inside-out patch clamp electrophysiology to monitor KCa current and channel activity.
  • Pharmacological agents including charybdotoxin, methylene blue, cystamine, 8-bromo-cGMP, and zaprinast were used.

Main Results:

  • NO increased whole-cell outward current by 79% and hyperpolarized smooth muscle cells.
  • NO increased the open probability (NPo) of KCa channels in on-cell patches, an effect blocked by charybdotoxin.
  • NO's effect on NPo was diminished by cGMP pathway inhibitors (methylene blue, cystamine) and mimicked by a cGMP analog (8-BrcGMP) and phosphodiesterase inhibitor (zaprinast).

Conclusions:

  • Nitric oxide activates KCa channels in rabbit colon circular smooth muscle.
  • This activation is mediated through a cGMP-dependent pathway.
  • NO-induced KCa channel activity contributes to the hyperpolarization of intestinal smooth muscle.

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