Time-resolved imaging of Ca(2+)-dependent aequorin luminescence of microdomains and QEDs in synaptic preterminals.
Localized elevation of intracellular free calcium [Ca2+]i concentration serves as the trigger for a wide variety of physiological processes, e.g., neurotransmitter release at most chemical synapses (1-3). The details of the mechanisms that regulate these processes are still unresolved (3-6), but they must involve precise temporal sequences of molecular events initiated by a transient localized elevation of Ca2+ concentration (i.e., a Ca2+ microdomain [3,7-15]). A microdomain is defined as an autonomous compartment of minimal spatio-temporal volume within which a signaled process can occur (8, 10, 12). A quantum emission domain (QED) is a quantal signal element (3, 16, 17). The concept of a QED was first applied to Ca2+ signaling at the synaptic preterminal (3, 4) and for large-diameter mitotic cells (16, 17). The concept of Ca2+ microdomains was tested by labeling preterminals of squid giant synapses with low-sensitivity aequorin (a photoprotein that emits a photon upon binding Ca2+ [18, 19]). That work confirmed earlier modeling efforts (10, 16) and showed that, upon depolarization, the [Ca2+]i profile reaches 200-300 microM within the microdomains, and that these [Ca2+]i profiles are composed of groups of short-lived 0.5 microns diameter QEDs. In those records, obtained with 2:1 interlacing devices operating at the RS-170 standard, QEDs appeared as striped dots or chevrons rather than as solid dots, indicating that a QED lasted less than 16.6 ms (one video field), and thus establishing the need for higher sampling rates to better characterize the QED.(ABSTRACT TRUNCATED AT 250 WORDS)
Section and Department of Physiology, Cornell University, Ithaca, New York 14853-6401.
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Lang
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D000331:Aequorin / Q000737:chemistry*; D000818:Animals; D002118:Calcium / Q000737:chemistry*; D049832:Decapodiformes; D007091:Image Processing, Computer-Assisted; D008163:Luminescent Measurements; D017729:Presynaptic Terminals / Q000737:chemistry*; D013997:Time Factors; D014743:Videotape Recording
D000331:Aequorin; D002118:Calcium