Two distinct Ca2+ influx pathways activated by the bradykinin B2 receptor.
The hormone-induced depletion of cellular Ca stores provides a signal for the Ca2+ influx into electrically non-excitable cells; however, the underlying molecular mechanisms remain elusive. Therefore, we analyzed bradykinin-activated Ca2+ influx into human foreskin fibroblast cells, HF-15, by fura-2 and 45Ca labeling to discriminate between Ca2+ influx into the fura-sensitive compartment and Ca uptake into fura-insensitive Ca stores. Bradykinin-activated Ca2+ influx into the fura-sensitive compartment was blocked by inhibitors of NO synthases. These inhibitors also suppressed bradykinin-activated increases in cGMP, indicating that the NO-dependent increase in cGMP is involved in the activation of the Ca2+ influx into the fura-sensitive compartment. The cGMP-dependent kinase inhibitors KT5823 and Rp-8-(parachlorophenylthio)-cGMP (Rp-8-pCPT-cGMPS) blocked bradykinin-activated Ca2+ influx into the fura-sensitive compartment, suggesting that a cGMP-dependent kinase step participates in the activation of this Ca2+ influx pathway. In addition to the NO/cGMP-mediated Ca2+ influx into the fura-sensitive compartment, bradykinin enhanced 45Ca uptake into Ca stores that were not accessible to fura-2. This enhanced 45Ca uptake was insensitive to blockers of the NO/cGMP pathway, indicating that the 45Ca uptake pathway is distinct from the NO-dependent Ca2+ influx into the fura-sensitive compartment. Furthermore, bradykinin enhanced 45Ca uptake into proliferating but not into quiescent HF-15 fibroblasts. Hence, bradykinin stimulates two distinct Ca2+ influx pathways in HF-15 cells, (a) Ca2+ influx into the fura-sensitive compartment which is NO/cGMP-dependent and (b) Ca uptake into Ca stores which bypasses the cytoplasm, which is NO insensitive and which is linked to cell proliferation.
AbdAlla
S
S
Institute of Physiological Chemistry and Pathobiochemistry, University of Mainz, Germany.
Müller-Esterl
W
W
Quitterer
U
U
D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002455:Cell Division; D002460:Cell Line; D006152:Cyclic GMP / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D007399:Interphase; D017136:Ion Transport / Q000187:drug effects; D009569:Nitric Oxide / Q000378:metabolism; D043782:Receptor, Bradykinin B2; D018002:Receptors, Bradykinin / Q000378:metabolism*
D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D043782:Receptor, Bradykinin B2; D018002:Receptors, Bradykinin; D009569:Nitric Oxide; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D001920:Bradykinin; D002118:Calcium; D016257:Fura-2