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 α1-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 μm·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 AIF4- 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.
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of Biological Chemistry|
|State||Published - Jul 24 1990|
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