title: Cytoplasmic Ca2+ determines the rate of Ca2+ entry into Mardin-Darby canine kidney-focus (MDCK-F) cells.
abstract: Transformed Mardin-Darby canine kidney-focus (MDCK-F) cells exhibit spontaneous Ca2+ oscillations from an inositol 1,4,5-triphosphate-sensitive cytoplasmic Ca2+ store. In this study, Ca2+ entry from the extracellular space and its role in generation of oscillations were investigated by means of Ca2+ video imaging and the Fura-2/Mn2+ quenching technique. Oscillations were dependent on extracellular Ca2+ concentration and were inhibited by extracellularly applied La3+, Co2+ and Ni2+. Depolarization of the cell membrane with high K+ concentrations and the L-type Ca2+ channel blocker nifedipine had no effect on oscillations, indicating the lack of involvement of voltage-gated Ca2+ channels. Mn2+ quenching experiments disclosed significant Ca2+ influx into MDCK-F cells. The rate of this influx was constant between Ca2+ spikes, but markedly increased during the spontaneous Ca2+ spikes. Similar transient increases in Ca2+ entry could be mimicked by agents triggering intracellular Ca2+ release such as bradykinin and thapsigargin. We conclude that the plasma membrane of MDCK-F cells exhibits a marked voltage-independent Ca2+ permeability permitting Ca2+ entry into the cytoplasm. The rate of Ca2+ entry which determines the frequency of oscillations is most likely to be regulated by the cytoplasmic Ca2+ concentration.
authors.affiliation: Department of Phsiology, University of Würzburg, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Wojnowski
authors.forename: A
authors.initials: A
authors.lastname: Schwab
authors.forename: J
authors.initials: J
authors.lastname: Hoyland
authors.forename: W T
authors.initials: WT
authors.lastname: Mason
authors.forename: S
authors.initials: S
authors.lastname: Silbernagl
authors.forename: H
authors.initials: H
authors.lastname: Oberleithner
mesh_terms: D000818:Animals; D001683:Biological Clocks / Q000502:physiology; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004285:Dogs; D005110:Extracellular Space / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D008345:Manganese / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
chemical_list: D013729:Terpenes; D008345:Manganese; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000252:Calcium-Transporting ATPases; D001920:Bradykinin; D002118:Calcium