Near-membrane [Ca super(2+)] transients resolved using the Ca super(2+) indicator FFP18

Ca super(2+)-sensitive processes at cell membranes involved in contraction, secretion, and neurotransmitter release are activated in situ or in vitro by Ca super(2+) concentrations ([Ca super(2+)]) 10-100 times higher than [Ca super(2+)] measured during stimulation in intact cells. This paradox migh...

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Published in:Proceedings of the National Academy of Sciences - PNAS 1996-01, Vol.93 (11), p.5368-5373
Main Authors: Etter, E F, Minta, A, Poenie, M, Fay, F S
Format: Article
Language:English
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Bufo marinus
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Summary:Ca super(2+)-sensitive processes at cell membranes involved in contraction, secretion, and neurotransmitter release are activated in situ or in vitro by Ca super(2+) concentrations ([Ca super(2+)]) 10-100 times higher than [Ca super(2+)] measured during stimulation in intact cells. This paradox might be explained if the local [Ca super(2+)] at the cell membrane is very different from that in the rest of the cell. Soluble Ca super(2+) indicators, which indicate spatially averaged cytoplasmic [Ca super(2+)], cannot resolve these localized, near-membrane [Ca super(2+)] signals. FFP18, the newest Ca super(2+) indicator designed to selectively monitor near-membrane [Ca super(2+)], has a lower Ca super(2+) affinity and is more water soluble than previously used membrane-associating Ca super(2+) indicators. Images of the intracellular distribution of FFP18 show that >65% is located on or near the plasma membrane. [Ca super(2+)] transients recorded using FFP18 during membrane depolarization-induced Ca super(2+) influx show that near-membrane [Ca super(2+)] rises faster and reaches micromolar levels at early times when the cytoplasmic [Ca super(2+)], recorded using fura-2, has risen to only a few hundred nanomolar. High-speed series of digital images of [Ca super(2+)] show that near-membrane [Ca super(2+)], reported by FFP18, rises within 20 msec, peaks at 50-100 msec, and then declines. [Ca super(2+)] reported by fura-2 rose slowly and continuously throughout the time images were acquired. The existence of these large, rapid increases in [Ca super(2+)] directly beneath the surface membrane may explain how numerous Ca super(2+)-sensitive membrane processes are activated at times when bulk cytoplasmic [Ca super(2+)] changes are too small to activate them.
ISSN:0027-8424