Near-membrane [Ca2+] transients resolved using the Ca2+ indicator FFP18
Department of Physiology and Biomedical Imaging Group
Animals; Bufo marinus; Calcium; Cell Membrane; Chelating Agents; Cytosol; Fluorescent Dyes; Fura-2; Kinetics; Mathematics; Membrane Potentials; Models, Biological; Muscle, Smooth; Patch-Clamp Techniques; Stomach
Life Sciences | Medicine and Health Sciences
(Ca2+)-sensitive processes at cell membranes involved in contraction, secretion, and neurotransmitter release are activated in situ or in vitro by Ca2+ concentrations ([Ca2+]) 10-100 times higher than [Ca2+] measured during stimulation in intact cells. This paradox might be explained if the local [Ca2+] at the cell membrane is very different from that in the rest of the cell. Soluble Ca2+ indicators, which indicate spatially averaged cytoplasmic [Ca2+], cannot resolve these localized, near-membrane [Ca2+] signals. FFP18, the newest Ca2+ indicator designed to selectively monitor near-membrane [Ca2+], has a lower Ca2+ affinity and is more water soluble than previously used membrane-associating Ca2+ indicators. Images of the intracellular distribution of FFP18 show that >65% is located on or near the plasma membrane. [Ca2+] transients recorded using FFP18 during membrane depolarization-induced Ca2+ influx show that near-membrane [Ca2+] rises faster and reaches micromolar levels at early times when the cytoplasmic [Ca2+], recorded using fura-2, has risen to only a few hundred nanomolar. High-speed series of digital images of [Ca2+] show that near-membrane [Ca2+], reported by FFP18, rises within 20 msec, peaks at 50-100 msec, and then declines. [Ca2+] reported by fura-2 rose slowly and continuously throughout the time images were acquired. The existence of these large, rapid increases in [Ca2+] directly beneath the surface membrane may explain how numerous (Ca2+)-sensitive membrane processes are activated at times when bulk cytoplasmic [Ca2+] changes are too small to activate them.
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Citation: Proc Natl Acad Sci U S A. 1996 May 28;93(11):5368-73.
Proceedings of the National Academy of Sciences of the United States of America
Etter, Elaine F.; Minta, Akwasi; Poenie, Martin; and Fay, Fredric S., "Near-membrane [Ca2+] transients resolved using the Ca2+ indicator FFP18" (1996). Open Access Articles. 1804.