title: Activation of maxi-anion channel by protein tyrosine dephosphorylation.
abstract: The maxi-anion channel with a large single-channel conductance of >300 pS, and unknown molecular identity, is functionally expressed in a large variety of cell types. The channel is activated by a number of experimental maneuvers such as exposing cells to hypotonic or ischemic stress. The most effective and consistent method of activating it is patch membrane excision. However, the activation mechanism of the maxi-anion channel remains poorly understood at present. In the present study, involvement of phosphorylation/dephosphorylation in excision-induced activation was examined. In mouse mammary fibroblastic C127 cells, activity of the channel was suppressed by intracellular application of Mg-ATP, but not Mg-5'-adenylylimidodiphosphate (AMP-PNP), in a concentration-dependent manner. When a cocktail of broad-spectrum tyrosine phosphatase inhibitors was applied, channel activation was completely abolished, whereas inhibitors of serine/threonine protein phosphatases had no effect. On the other hand, protein tyrosine kinase inhibitors brought the channel out of an inactivated state. In mouse adult skin fibroblasts (MAFs) in primary culture, similar maxi-anion channels were found to be activated on membrane excision, in a manner sensitive to tyrosine phosphatase inhibitors. In MAFs isolated from animals deficient in receptor protein tyrosine phosphatase (RPTP)zeta, activation of the maxi-anion channel was significantly slower and less prominent compared with that observed in wild-type MAFs; however, channel activation was restored by transfection of the RPTPzeta gene. Thus it is concluded that activation of the maxi-anion channel involves protein dephosphorylation mediated by protein tyrosine phosphatases that include RPTPzeta in mouse fibroblasts, but not in C127 cells.
authors: Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
authors: Abduqodir H
authors: AH
authors: Toychiev
authors: Ravshan Z
authors: RZ
authors: Sabirov
authors: Nobuyaki
authors: N
authors: Takahashi
authors: Yuhko
authors: Y
authors: Ando-Akatsuka
authors: Hongtao
authors: H
authors: Liu
authors: Takafumi
authors: T
authors: Shintani
authors: Masaharu
authors: M
authors: Noda
authors: Yasunobu
authors: Y
authors: Okada
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology / Q000502:physiology; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology / Q000502:physiology; D000818:Animals; D000838:Anions / Q000378:metabolism; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D015640:Ion Channel Gating; D007473:Ion Channels / Q000378:metabolism*; D008274:Magnesium; D051379:Mice; D010766:Phosphorylation; D054633:Receptor-Like Protein Tyrosine Phosphatases, Class 5 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D000838:Anions; D004791:Enzyme Inhibitors; D007473:Ion Channels; D000266:Adenylyl Imidodiphosphate; D014443:Tyrosine; D000255:Adenosine Triphosphate; D054633:Receptor-Like Protein Tyrosine Phosphatases, Class 5; D008274:Magnesium