Voltage sensitivity of slow wave frequency in isolated circular muscle strips from guinea pig gastric antrum

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 c hanging the extracellular K+ concentration (2-18 mM), the frequency of slow waves decreased and increased, respectively. Application of cromakalim hyp erpolarized the cell membrane and reduced the frequency of slow waves in a dose-dependent manner. Cromakalim (3 mu M) hyperpolarized the membrane, and slow waves ceased in most preparations. In the presence of cromakalim, sub sequent increases in the extracellular K+ concentration restored the freque ncy of slow waves accompanied by depolarization. Also, glibenclamide comple tely antagonized this effect of cromakalim. In smooth muscle strips contain ing both circular and longitudinal muscle layers, such changes in the slow wave frequency were not observed. It was concluded that the maneuver of iso lating circular smooth muscle altered the voltage dependence of the slow wa ve frequency.