title: A novel Ca2+ entry mechanism is turned on during growth arrest induced by Ca2+ pool depletion.
abstract: Ca2+ pool depletion with Ca2+ pump blockers induces growth arrest of rapidly dividing DDT1MF-2 smooth muscle cells and causes cells to enter a stable, quiescent G0-like growth state (Short, A.D., Bian, J., Ghosh, T.K., Waldron, R.T., Rybak, S.L., and Gill, D.L. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 4986-4990). Here we reveal that induction of this quiescent growth state with the Ca2+ pump blocker, thapsigargin, is correlated with the appearance of a novel caffeine-activated Ca2+ influx mechanism. Ca2+ influx through this mechanism is clearly distinct from and additive with Ca2+ entry through store-operated channels (SOCs). Whereas SOC-mediated entry is activated seconds after Ca2+ pool release, caffeine-sensitive influx requires at least 30 min of pool emptying. Although activated in the 1-10 mM caffeine range, this mechanism has clearly distinct methylxanthine specificity from ryanodine receptors and is not modified by ryanodine. It is also unaffected by the Ca2+ channel blockers SKF96365 or verapamil and is independent of modifiers of cyclic nucleotide levels. Growth arrest by thapsigargin-induced Ca2+ pool depletion can be reversed by treatment with 20% serum (Waldron, R.T., Short, A.D., Meadows, J.J., Ghosh, T.K., and Gill, D.L. (1994) J. Biol. Chem. 269, 11927-11933). The serum-induced return of functional Ca2+ pools and reentry of cells into the cell cycle correlates exactly with the disappearance of the caffeine-sensitive Ca2+ influx mechanism. Therefore, appearance and function of this novel Ca2+ entry mechanism are closely tied to Ca2+ pool function and cell growth state and may provide an important means for modifying exit from or entry into the cell cycle.
authors.affiliation: Department of Biological Chemistry, University of Maryland School of Medicine, Baltimore 21201, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Ufret-Vincenty
authors.forename: A D
authors.initials: AD
authors.lastname: Short
authors.forename: A
authors.initials: A
authors.lastname: Alfonso
authors.forename: D L
authors.initials: DL
authors.lastname: Gill
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D006224:Cricetinae; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D008297:Male; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D016192:Resting Phase, Cell Cycle / Q000187:drug effects; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014970:Xanthines / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D013729:Terpenes; D014970:Xanthines; D002110:Caffeine; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium