The surface cyclic AMP receptors, cAR1, cAR2, and cAR3, promote Ca2+ influx in Dictyostelium discoideum by a G alpha 2-independent mechanism.
Activation of surface folate receptors or cyclic AMP (cAMP) receptor (cAR) 1 in Dictyostelium triggers within 5-10 s an influx of extracellular Ca2+ that continues for 20 s. To further characterize the receptor-mediated Ca2+ entry, we analyzed 45Ca2+ uptake in amoebas overexpressing cAR2 or cAR3, cARs present during multicellular development. Both receptors induced a cAMP-dependent Ca2+ uptake that had comparable kinetics, ion selectivity, and inhibitor profiles as folate- and cAR1-mediated Ca2+ uptake. Analysis of mutants indicated that receptor-induced Ca2+ entry does not require G protein alpha subunits G alpha 1, G alpha 2, G alpha 3, G alpha 4, G alpha 7, or G alpha 8. Overexpression of cAR1 or cAR3 in g alpha 2- cells did not restore certain G alpha 2-dependent events, such as aggregation, or cAMP-mediated activation of adenylate and guanylate cyclases, but these strains displayed a cAMP-mediated Ca2+ influx with kinetics comparable to wild-type aggregation-competent cells. These results suggest that a plasma membrane-associated Ca(2+)-influx system may be activated by at least four distinct chemoreceptors during Dictyostelium development and that the response may be independent of G proteins.
Milne
J L
JL
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Devreotes
P N
PN
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004023:Dictyostelium / Q000378:metabolism*; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D017136:Ion Transport; D007700:Kinetics; D011956:Receptors, Cell Surface; D011953:Receptors, Cyclic AMP / Q000378:metabolism*; D015398:Signal Transduction
D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D011953:Receptors, Cyclic AMP; D005492:Folic Acid; D019204:GTP-Binding Proteins; D002118:Calcium