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.
Institute of Physiological Chemistry and Pathobiochemistry, University of Mainz, Germany.
S
S
AbdAlla
W
W
Müller-Esterl
U
U
Quitterer
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