Agonist-dependent patterns of cytosolic Ca2+ changes in single bovine adrenal chromaffin cells: relationship to catecholamine release.
The patterns of agonist-induced elevations of cytosolic free Ca2+ ([Ca2+]i) were characterized and compared by the use of single adrenal chromaffin cells. Initial histamine- or angiotensin II (AII)-induced elevations of [Ca2+]i were equal in magnitude (peaks 329 +/- 20 [SE] and 338 +/- 46 nM, respectively). These initial increases of [Ca2+]i were transient, insensitive to either Gd3+ or removing external Ca2+, and were primarily the result of Ca2+ release from intracellular stores. After the initial peak(s) of [Ca2+]i, a second phase of moderately elevated [Ca2+]i was observed, and this response was sensitive to either Gd3+ or removing external Ca2+, supporting a role for Ca2+ entry. In most cases, the second phase of elevated [Ca2+]i was sustained during histamine stimulation but transient during AII stimulation. Maintenance of the second phase was a property of the agonist rather than of the particular cell being stimulated. Thus, individual cells exposed sequentially to histamine and AII displayed distinct patterns of [Ca2+]i changes to each agonist, regardless of the order of addition. Histamine also stimulated twice as much [3H]catecholamine release as AII, and release was completely dependent on external Ca2+. Therefore, the ability of histamine and AII to sustain (or promote) Ca2+ entry appears to underlie their efficacy as secretagogues. These data provide evidence linking agonist-dependent patterns of [Ca2+]i changes in single cells with agonist-dependent functional responses.
Stauderman
K A
KA
Merrell Dow Research Institute, Cincinnati, Ohio 45215.
Murawsky
M M
MM
Pruss
R M
RM
D000313:Adrenal Medulla / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D002837:Chromaffin Granules / Q000187:drug effects / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004553:Electric Conductivity; D006632:Histamine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*
D002021:Buffers; D000804:Angiotensin II; D006632:Histamine; D002118:Calcium; D009638:Norepinephrine