Inhibition of Ca(2+) entry caused by depolarization in acetylcholine-stimulated antral mucous cells of guinea pig: G protein regulation of Ca(2+) permeable channels.
The effects of depolarizing conditions resulting from increasing extracellular K(+) concentration or nystatin treatment on intracellular Ca(2+) concentration ([Ca(2+)](i)) were studied in guinea pig antral mucous cells following acetylcholine (ACh) stimulation. ACh stimulation evoked a biphasic increase in [Ca(2+)](i), that is, an initial transient increase followed by a plateau. Depolarizing conditions reduced the [Ca(2+)](i) in the plateau phase during ACh stimulation. However, pertussis toxin (PTX, a G protein inhibitor) treatment caused [Ca(2+)](i) in the ACh-evoked plateau phase to increase under depolarizing conditions, while it had no effect on [Ca(2+)](i) under hyperpolarized conditions. Based on these observations, Ca(2+) permeable channels are regulated by a G protein which is activated by depolarized conditions and inhibited by hyperpolarized conditions and PTX; activation of the G protein (depolarization) causes Ca(2+) permeable channels to inhibit, and in turn, inhibition of the G protein (hyperpolarization) causes them to activate.
Nakahari
T
T
Department of Physiology, Osaka Medical College, Takatsuki, 569-8686, Japan. takan@art.osaka-med.ac.jp.
Yoshida
H
H
Imai
Y
Y
Fujiwara
S
S
Ohnishi
A
A
Shimamoto
C
C
Katsu
K i
Ki
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000235:genetics*; D005753:Gastric Mucosa / Q000502:physiology*; D006168:Guinea Pigs; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects
D015220:Calcium Channels; D019204:GTP-Binding Proteins; D000109:Acetylcholine