Depletion and filling of intracellular calcium stores in vascular smooth muscle.
In vascular smooth muscle, binding of vasoactive substances to surface membrane receptors leads to a rise of intracellular cytoplasmic Ca2+ and to contraction. Cytoplasmic free Ca2+ concentration ([Ca2+]i) increases through release of Ca2+ from intracellular stores and Ca2+ entry through surface membrane ion channels. Membrane-permeant and membrane-impermeant forms of fura 2 were used to distinguish changes in intracellularly stored Ca2+ ([Ca2+]s) from changes in [Ca2+]i. The spatiotemporal patterns of the movement of Ca2+ between these two cellular compartments in cultured vascular smooth muscle cells (A7r5 cell line) were visualized with digital imaging fluorescence microscopy. The Ca2+ stores were localized by double staining with a fluorescent organelle-specific dye and the Ca2+ indicator. [Ca2+]s was measured after accumulation of the membrane-permeant form of fura 2 inside the stores and quenching of the fura 2 fluorescence in the cytoplasmic compartment with manganese. Stimulation with vasopressin led to a transient increase of [Ca2+]i and a concomitant decrease of [Ca2+]s. After stimulation with vasopressin, [Ca2+]i returned rapidly to normal resting levels, whereas the recovery of [Ca2+]s occurred on a much slower time scale. The refilling pathway of depleted stores involved Ca2+ entry into the bulk cytoplasmic compartment before uptake into the stores.
Blatter
L A
LA
Department of Physiology, Loyola University Chicago, Maywood, Illinois 60153.
D001127:Arginine Vasopressin / Q000494:pharmacology; D002118:Calcium / Q000172:deficiency* / Q000378:metabolism*; D002460:Cell Line; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D007425:Intracellular Membranes / Q000378:metabolism*; D008345:Manganese / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors; D014018:Tissue Distribution
D005456:Fluorescent Dyes; C049925:fura-2-am; D001127:Arginine Vasopressin; D008345:Manganese; D002118:Calcium; D016257:Fura-2