Functionally and spatially distinct Ca2+ stores are revealed in cultured vascular smooth muscle cells.
Sarcoplasmic reticulum Ca2+ in vascular smooth muscle may be separated into at least two types of Ca2+ stores, one releasable by inositol 1,4,5-trisphosphate and the other releasable by caffeine and ryanodine. We employed digital imaging with fura-2 to study the effects of thapsigargin (which blocks Ca2+ sequestration in the inositol trisphosphate-sensitive store) and caffeine on the cytosolic free Ca2+ concentration ([Ca2+]cyt) in cultured arterial myocytes. These agents increased [Ca2+]cyt by depleting different Ca2+ stores in the absence of extracellular Ca2+. Moreover, Ca2+ could be transferred between the two stores, as prior application of caffeine, which alone evoked little or no rise in [Ca2+]cyt, significantly augmented the response to thapsigargin. Conversely, a substantial caffeine-induced rise in [Ca2+]cyt was observed only after the ability of the thapsigargin-sensitive Ca2+ store to sequester Ca2+ was inhibited. This suggests that the caffeine-sensitive store may have a thapsigargin-insensitive Ca(2+)-sequestration mechanism. To complement these fura-2 experiments, chlortetracycline was used to visualize the Ca2+ stores directly. The latter studies revealed spatial differences in the location of the thapsigargin-sensitive and caffeine-sensitive Ca2+ stores (measured as thapsigargin-sensitive and caffeine-sensitive chlortetracycline fluorescence). Thus, these two types of stores appear to be both functionally and spatially distinct.
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201.
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D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002460:Cell Line; D002478:Cells, Cultured; D005333:Fetus; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology; D007700:Kinetics; D008856:Microscopy, Fluorescence; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012433:Ryanodine / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013997:Time Factors
D013729:Terpenes; D012433:Ryanodine; D002110:Caffeine; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium