Pharmaco-mechanical coupling in the iris sphincter muscle

Research Project

Project/Area Number	61571059
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	Biological pharmacy
Research Institution	Nagoya City University
Principal Investigator	WATANABE Minoru Faculty of Phamaceut. Sciences, Nagoya City University, 薬学部, 教授 (50012638)
Co-Investigator(Kenkyū-buntansha)	KAWAI Tomoyuki Faculty of Pharmaceut. Sciences, Nagoya City University, 薬学部, 助手 (60152906)
Project Period (FY)	1986 – 1987
Project Status	Completed (Fiscal Year 1987)
Budget Amount *help	¥2,000,000 (Direct Cost: ¥2,000,000) Fiscal Year 1987: ¥1,000,000 (Direct Cost: ¥1,000,000) Fiscal Year 1986: ¥1,000,000 (Direct Cost: ¥1,000,000)
Keywords	Iris sphincter / Patch clamp / イオン電流 / 単一細胞 / 膜電流
Research Abstract	Ionic currents in single smooth muscle cells isolated from rabbit iris sphincter were investigated using the single suction electrode voltage clamp method. By depolarization from holding potential of -60mV, only outward currents were activated. The main component of the outward currents was blocked by 3mM tetraethylammonium (TEA) or withdrawal of extracelular Ca. The transient component of residual outward currents was inhibited by 3mM 4-aminopyridine (4-AP). Outward currents were totally abolished by 50mM TEA and 5mM 4-AP. The inward current could be unmasked by the treatment with 50mM TEA and 5mM 4-AP, but was still quite small (<20pA). When extracellular Ca concentration was elevated from 2.2 to 10mM, the inward current was enhanced by about threefold. The replacement of Ca with Ba enlarged the peak inward current and decreased the decaying time course. The large outward currents in comparison with the small inward current can explain the lack of excitability of this smooth muscle under physiological conditions.