Agonist-induced cytosolic calcium oscillations originate from a specific locus in single hepatocytes.
Digital imaging fluorescence microscopy of fura-2-loaded hepatocytes in primary culture has been used to examine the changes of cytosolic free Ca2+ ([Ca2+]i) in response to receptor activation by alpha 1-adrenergic agonists and vasopressin at the subcellular level. Agonist-induced Ca2+ oscillations did not occur synchronously within the cell but originated from a specific region adjacent to the cell membrane and then propagated throughout the rest of the cell, with each oscillation within a series originating from the same locus. Furthermore, hormones acting through different receptors produced Ca2+ waves with similar rates of progress (20-25 microns.s-1) which originated from the same subcellular locus. For a given cell, the rate of progress and amplitude of the Ca2+ waves were independent of applied agonist concentration and were unaffected by depletion of extracellular Ca2+. The kinetics of Ca2+ increase at different points within the cell indicated that the Ca2+ waves were not driven by diffusion but were characteristic of a self-propagating mechanism. Significantly, when cells were treated with A1F-4 to directly activate the G-protein which couples receptor occupancy to [Ca2+]i mobilization, the origin and kinetics of the Ca2+ waves were identical to those observed with hormonal stimulation. It is proposed that the spatial organization of the intracellular Ca2+ release mechanisms may have significance in the regulation of the asymmetric metabolic functions of hepatocytes and other functionally polarized cells.
Rooney
T A
TA
Department of Pathology and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Sass
E J
EJ
Thomas
A P
AP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D005456:Fluorescent Dyes; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009991:Oscillometry; D010656:Phenylephrine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012969:Sodium Fluoride / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D014667:Vasopressins / Q000494:pharmacology
D005456:Fluorescent Dyes; D014667:Vasopressins; D010656:Phenylephrine; D004533:Egtazic Acid; D012969:Sodium Fluoride; D002118:Calcium