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Departments of 1 Physiology and
2 Anatomy,
In circular muscle preparations isolated from
the guinea pig gastric antrum, regular spontaneous electrical activity
(slow waves) was recorded. Under normal conditions (6 mM
K+), the frequency and shape of
the slow waves were similar to those observed in ordinary stomach
smooth muscle preparations. When the resting membrane potential was
hyperpolarized and depolarized by changing the extracellular
K+ concentration (2-18 mM),
the frequency of slow waves decreased and increased, respectively.
Application of cromakalim hyperpolarized the cell membrane and reduced
the frequency of slow waves in a dose-dependent manner. Cromakalim (3 µM) hyperpolarized the membrane, and slow waves ceased in most
preparations. In the presence of cromakalim, subsequent increases in
the extracellular K+ concentration
restored the frequency of slow waves accompanied by depolarization.
Also, glibenclamide completely antagonized this effect of cromakalim.
In smooth muscle strips containing both circular and longitudinal
muscle layers, such changes in the slow wave frequency were not
observed. It was concluded that the maneuver of isolating circular
smooth muscle altered the voltage dependence of the slow wave frequency.
pacemaker; smooth muscle; voltage dependence; potassium channel opener
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