Hypoxia differentially modulates the activity of pacemaker and smooth muscle cells in the guinea pig stomach antrum.
Effects of hypoxic solution (O(2) tension, 161 +/- 11 mmHg) on electrical responses of the membrane (slow waves), intracellular Ca(2+)-responses measured by Fura-2 fluorescence (Ca-transients) and isometric mechanical responses (phasic contraction) were observed in circular smooth muscles isolated from the guinea-pig stomach antrum. In normoxic solution (O(2) tension, 362 +/- 28 mmHg), muscle cells generated slow waves spontaneously, and switching to hypoxic solution caused an increase in frequency and decrease in duration of slow waves, with no significant change in the resting membrane potential. Hypoxia also reduced the amplitude and duration and increased the frequency of Ca-transients. The increase in frequency of slow waves by hypoxia was prevented by cyclopiazonic acid (CPA) but not by carbonyl cyanide m-chlorophenyl-hydrazone (CCCP), potassium cyanide (KCN) or low-Ca solution. The reduction by hypoxia of the duration of slow waves was prevented by CCCP or KCN but not by CPA or low-Ca solution. Hypoxia resulted in an increase in frequency and decrease in amplitude of phasic contractions, and the changes were prevented by CPA but not by CCCP. These results suggested that in antrum smooth muscle tissues, the increase in frequency of spontaneous activity by hypoxia is related to the enhanced function of the CPA-sensitive internal Ca-stores in pacemaker cells, while the inhibition in amplitude of phasic contractions by hypoxia may be mainly related to the decrease in Ca(2+) release from the CPA-sensitive internal stores in smooth muscle cells. It is concluded that in hypoxic solution, the function of internal Ca(2+) stores is enhanced in ICC-MY and is inhibited in smooth muscle cells in the guinea-pig stomach antrum.
Nakamura
Eri
E
Department of Physiology, Nagoya City University, Mizuho-ku, Nagoya, Japan. eririn@med.nagoya-cu.ac.jp
Yokoi
Tsuyoshi
T
Fukuta
Hiroyasu
H
Iida
Takao
T
Tanaka
Yasuo
Y
Yamamoto
Yoshimichi
Y
Suzuki
Hikaru
H
D000818:Animals; D002118:Calcium / Q000008:administration & dosage / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D055724:Electrophysiological Phenomena / Q000187:drug effects; D016257:Fura-2; D006168:Guinea Pigs; D000860:Hypoxia / Q000503:physiopathology*; D007211:Indoles / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011190:Potassium Cyanide / Q000494:pharmacology; D011706:Pyloric Antrum / Q000187:drug effects / Q000502:physiology*
D007211:Indoles; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D011190:Potassium Cyanide; D002118:Calcium; D016257:Fura-2; C000543:cyclopiazonic acid