Factors modifying the frequency of spontaneous activity in gastric muscle.
The cellular mechanisms that determine the frequency of spontaneous activity were investigated in gastric smooth muscles isolated from the guinea-pig. Intact antral muscle generated slow waves periodically; the interval between slow waves was decreased exponentially by depolarization of the membrane to reach a steady interval value of about 7 s. Isolated circular muscle bundles produced slow potentials spontaneously or were evoked by depolarizing current stimuli. Evoked slow potentials appeared in an all-or-none fashion, with a refractory period of approximately 2-3 s. Low concentrations of chemicals that modify intracellular signalling revealed that the refractory period was causally related to the activity of protein kinase C (PKC). Activation of PKC increased and inhibition of PKC activity decreased the frequency of slow potentials. Chemicals that inhibit mitochondrial functions reduced the frequency of slow waves. Inhibition of internal Ca(2+)-store activity decreased the amplitude, but not the frequency of slow potentials, suggesting that the amplitude is causally related to Ca(2+) release from the internal store. The results suggest that changes in [Ca(2+)](i) caused by the activity of mitochondria may play a key role in determining the frequency of spontaneous activity in gastric pacemaker cells.
Suzuki
H
H
Department of Physiology, Nagoya City University Medical School, Mizuho-ku, Nagoya 467-8601, Japan. hisuzuki@med.nagoya-cu.ac.jp
Kito
Y
Y
Hashitani
H
H
Nakamura
E
E
D000818:Animals; D001683:Biological Clocks / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology; D005071:Evoked Potentials / Q000502:physiology; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000294:innervation* / Q000502:physiology; D016065:Myoelectric Complex, Migrating / Q000502:physiology*; D011493:Protein Kinase C / Q000502:physiology; D011706:Pyloric Antrum / Q000166:cytology / Q000294:innervation / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D013270:Stomach / Q000166:cytology / Q000294:innervation* / Q000502:physiology
D011493:Protein Kinase C; D002118:Calcium