title: Two types of external Cl(-)-dependent Cl(-) channels and one type of stretch receptor cation channel contribute to the formation of isotonic blastocoel fluid in early medaka fish embryo.
abstract: Ionic channels in blastoderm cells dissociated from medaka fish embryos at the late blastula stage were studied by the patch-clamp technique in whole-cell, inside-out and cell-attached patch configurations. These cells were mechanically dissociated without using proteo-lytic enzymes. I have reported previously an external anion-dependent type I Cl(-) channel, which was observed at the early blastula stage, and its voltage dependency shifted toward the positive direction with a reduction in [Cl(-)](o). The type I Cl(-) channel was observed in about half of the blastoderm cells at the late blastula stage. I also observed another external anion-dependent Cl(-) channel (type II) whose voltage dependency shifted toward the negative direction with a reduction in [Cl(-)](o) and a cation selective stretchactivated channel. The$coexistence of the type II Cl(-) channel and stretch-activated cation channel would produce the efflux of both cations and anions in response to low ionic strength fluid. Further, the initial rise of blastocoel [Cl(-)] by this mechanism would trigger positive feedback between the type I Cl(-) channel conductance and blastocoel [Cl(-)]. At the early blastula stage, the blastocoel cavity fluid has a low ionic strength similar to that of pond water. I proposed that the cooperation of three types of ion channels at the late blastula stage generates isotonic blastocoel cavity fluid.
authors.affiliation: Department of Physiology, School of Medicine, Kobe University, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Shigemoto
mesh_terms: D000818:Animals; D001756:Blastoderm / Q000502:physiology; D018118:Chloride Channels / Q000502:physiology*; D002712:Chlorides / Q000502:physiology; D004625:Embryo, Nonmammalian / Q000502:physiology*; D017136:Ion Transport / Q000502:physiology; D008465:Mechanoreceptors / Q000502:physiology; D009990:Oryzias / Q000196:embryology / Q000502:physiology*
chemical_list: D018118:Chloride Channels; D002712:Chlorides