1992 Fiscal Year Final Research Report Summary
Effects of intracellular pH on exitability of smooth muscle
| Project/Area Number |
02454116
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
General physiology
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| Research Institution | Nagoya University |
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Principal Investigator |
TOMITA Tadao Nagoya University,Dept of Physiol. Professor, 医学部, 教授 (50078763)
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| Co-Investigator(Kenkyū-buntansha) |
TOKUNO Hiroyuki Nagoya Univ.Dept.Physiol.Res.Ass., 医学部, 助手 (60155520)
TAKAI Akira Nagoya Univ.,Dept. Physiol.Ass. Prof., 医学部, 助教授 (50126869)
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| Project Period (FY) |
1990 – 1992
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| Keywords | Smooth muscle / Intracellular pH / Contraction / Membrane current / Intracellular Ca / Na-H exchange / Na-Ca exchange / Cl-HCO_3 exchange |
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| Research Abstract |
Effects of changes in intracellular pH (pH_i) were studied in several vascular smooth muscles. pHi was estimated by measuring absorption spectrum of a pH-sensitive dye (Me_2CF) intracellularly loaded and membrane currents were measured with the whole-cell clamp method. pH_i increased from 7.2 to 7.6-7.8 during application of NH_4C1 (20 mM) and transiently decreased to 6.7-6.8 after wash-out. Intracellular alkalinization and acidification were accompanied by a slow contraction and a transient contraction. The former was significantly inhibited by phenoxybenzamine, an a-adrenoceptor blocking agent, suggesting a partial contribution of noradrenaline released from intrinsic nerves. When applied during a maintained muscle tone in excess K^+ medium, NH_4C1 produced relaxation. The contraction observed during intracellular acidification was not affected by verapamil, Ca^<2+> channel blocker, but strongly inhibited by removal of the external Ca^<2+>. This suggests that an increase in intracellular H^+ concentration ([H^+]_i) increases Ca^<2+> influx. It is possible that this is due to a secondary activation of Na-Ca exchange, resulting from an increased intracellular Na^+ concentration through Na-H exchange, activated by an increased [H^+]_i.
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[Publications] Hayashi,T., Shigetomi,T., Ueda,M., Kaneda,T., Matsumoto,T., Tokuno,H. and Tomita,T.: "Effects of ammonium chloride on membrane currents of acinar cells dispersed from the rat parotid gland." Pflugers Archiv. 420. 297-301 (1992)
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