Calcium gradients in single smooth muscle cells revealed by the digital imaging microscope using Fura-2.
Calcium is believed to control a variety of cellular processes, often with a high degree of spatial and temporal precision. For a cell to use Ca2+ in this manner, mechanisms must exist for controlling the ion in a localized fashion. We have now gained insight into such mechanisms from studies which measured Ca2+ in single living cells with high resolution using a digital imaging microscope and the highly fluorescent Ca2+-sensitive dye, Fura-2. Levels of Ca2+ in the cytoplasm, nucleus and sarcoplasmic reticulum (SR) are clearly different. Free [Ca2+] in the nucleus and SR was greater than in the cytoplasm and these gradients were abolished by Ca2+ ionophores. When external Ca2+ was raised above normal in the absence of ionophores, free cytoplasmic Ca2+ increased but nuclear Ca2+ did not. Thus, nuclear [Ca2+] appears to be regulated independently of cytoplasmic [Ca2+] by gating mechanisms in the nuclear envelope. The observed regulation of intranuclear Ca2+ in these contractile cells may thus be seen as a way to prevent fluctuation in Ca2+-linked nuclear processes during the rise in cytoplasmic [Ca2+] which triggers contraction. The approach described here offers the opportunity of following changes in Ca2+ in cellular compartments in response to a wide range of stimuli, allowing new insights into the role of local changes in Ca2+ in the regulation of cell function.
D000818:Animals; D001572:Benzofurans; D002024:Bufo marinus; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation / Q000187:drug effects; D002467:Cell Nucleus / Q000378:metabolism; D004987:Ethers / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D016257:Fura-2; D015759:Ionomycin; D008564:Membrane Potentials; D008856:Microscopy, Fluorescence / Q000295:instrumentation; D009130:Muscle, Smooth / Q000502:physiology*; D012508:Sarcolemma / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D001572:Benzofurans; D004987:Ethers; D015759:Ionomycin; D002118:Calcium; D016257:Fura-2