title: The phospholipase C inhibitor U73122 increases cytosolic calcium in MDCK cells by activating calcium influx and releasing stored calcium.
abstract: The effects of the phospholipase C (PLC) inhibitor U73122 on intracellular calcium levels ([Ca2+]i) were studied in MDCK cells. U73122 elevated [Ca2+]i dose-dependently. Ca2+ influx contributed to 75% of 20 microM U73122-induced Ca2+ signals. U73122 pretreatment abolished the [Ca2+]i transients evoked by ATP and bradykinin, suggesting that U73122 inhibited PLC. The Ca2+ signals among individual cells varied considerably. The internal Ca2+ source for the U73122 response was the endoplasmic reticulum (ER) since the response was abolished by thapsigargin. The depletion of the ER Ca2+ store triggered a La3+-sensitive capacitative Ca2+ entry. Independently of the internal release and capacitative Ca2 entry, U73122 directly evoked Ca2+ influx through a La3+-insensitive pathway. The U73122 response was augmented by pretreatment of carbonylcyanide m-chlorophynylhydrozone (CCCP), but not by Na+ removal, implicating that mitochondria contributed significantly in buffering the Ca2+ signal, and that efflux via Na+/Ca2+ exchange was insignificant.
authors.affiliation: Department of Medical Education and Research, Veterans General Hospital-Kaohsiung, National Sun Yat-Sen University, Taiwan, ROC. crjan@isca.vghks.gov.tw
authors.forename: C R
authors.initials: CR
authors.lastname: Jan
authors.forename: C M
authors.initials: CM
authors.lastname: Ho
authors.forename: S N
authors.initials: SN
authors.lastname: Wu
authors.forename: C J
authors.initials: CJ
authors.lastname: Tseng
mesh_terms: D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004963:Estrenes / Q000494:pharmacology*; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D007811:Lanthanum / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D011760:Pyrrolidinones / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors*
chemical_list: D004791:Enzyme Inhibitors; D004963:Estrenes; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D007811:Lanthanum; D010738:Type C Phospholipases; D001920:Bradykinin; D002118:Calcium