title: Differential tyrosine phosphorylation of plasma membrane Ca2+-ATPase and regulation of calcium pump activity by carbachol and bradykinin.
abstract: We investigated the effects of thapsigargin (TG), bradykinin (BK), and carbachol (CCh) on Ca(2+) entry via endogenous channels in human embryonic kidney BKR21 cells. After depletion of Ca(2+) stores by either TG, BK, or CCh, the addition of Ca(2+) gave a much larger rise in Ca(2+) levels in CCh-treated and TG-treated cells than in cells treated with BK. However, in experiments performed with Ba(2+), a cation not pumped by Ca(2+)-ATPases, only a modest difference between CCh- and BK-stimulated Ba(2+) entry levels was observed, suggesting that the large difference in the Ca(2+) response is mediated by a differential regulation of Ca(2+) pump activity by CCh and BK. This hypothesis is supported by the finding that when Ca(2+) is removed during the stable, CCh-induced Ca(2+) plateau phase, the decline of cytosolic Ca(2+) is much faster in the absence of CCh than in its presence. In addition, if Ca(2+) is released from a caged Ca(2+) compound after a UV pulse, the resulting Ca(2+) peak is much larger in the presence of CCh than in its absence. Thus, the large increase in Ca(2+) levels observed with CCh results from both the activation of Ca(2+) entry pathways and the inhibition of Ca(2+) pump activity. In contrast, BK has the opposite effect on Ca(2+) pump activity. If Ca(2+) is released from a caged Ca(2+) compound, the resulting Ca(2+) peak is much smaller in the presence of BK than in its absence. An investigation of tyrosine phosphorylation levels of the plasma membrane Ca(2+)-ATPase (PMCA) demonstrated that CCh stimulates an increase in tyrosine phosphorylation levels, which has been reported to inhibit Ca(2+) pump activity, whereas in contrast, BK stimulates a reduction of PMCA tyrosine phosphorylation levels. Thus, BK and CCh have a differential effect both on Ca(2+) pump activity and on tyrosine phosphorylation levels of the PMCA.
authors.affiliation: Department of Neurobiology, Pharmacology, and Physiology, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: György
authors.initials: G
authors.lastname: Babnigg
authors.forename: Tatiana
authors.initials: T
authors.lastname: Zagranichnaya
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Wu
authors.forename: Mitchel L
authors.initials: ML
authors.lastname: Villereal
mesh_terms: D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology*; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D010766:Phosphorylation / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D014443:Tyrosine; D019284:Thapsigargin; D002217:Carbachol; D000252:Calcium-Transporting ATPases; D001920:Bradykinin; D002118:Calcium