Two distinct Ca2+ influx pathways activated by the bradykinin B2 receptor

Area of Science:

• Cell Biology
• Physiology
• Biochemistry

Background:

• Hormone-induced depletion of cellular calcium (Ca) stores signals for Ca2+ influx in non-excitable cells.
• The precise molecular mechanisms governing this Ca2+ influx remain incompletely understood.

Purpose of the Study:

• To investigate the mechanisms of bradykinin-activated Ca2+ influx in human foreskin fibroblast cells (HF-15).
• To differentiate between Ca2+ influx into the fura-2-sensitive compartment and Ca uptake into fura-2-insensitive stores.

Main Methods:

• Utilized fura-2 and 45Ca labeling to track Ca2+ dynamics in HF-15 cells.
• Employed inhibitors of nitric oxide (NO) synthases and cGMP-dependent kinase (e.g., KT5823, Rp-8-pCPT-cGMPS).
• Assessed Ca2+ influx and uptake in both proliferating and quiescent HF-15 fibroblasts.

Main Results:

• Bradykinin-activated Ca2+ influx into the fura-sensitive compartment was inhibited by NO synthase inhibitors and cGMP-dependent kinase inhibitors.
• This influx was associated with increased cyclic guanosine monophosphate (cGMP) levels, indicating an NO/cGMP-dependent pathway.
• Bradykinin also enhanced 45Ca uptake into fura-insensitive stores, a process insensitive to NO/cGMP pathway blockers and linked to cell proliferation.

Conclusions:

• Bradykinin stimulates two distinct Ca2+ influx pathways in HF-15 cells.
• Pathway 1: NO/cGMP-dependent Ca2+ influx into the fura-sensitive compartment.
• Pathway 2: NO-insensitive Ca uptake into stores, bypassing the cytoplasm and associated with proliferation.