Imaging calcium entering the cytosol through a single opening of plasma membrane ion channels: SCCaFTs--fundamental calcium events.
Recently, it has become possible to record the localized fluorescence transient associated with the opening of a single plasma membrane Ca(2+) permeable ion channel using Ca(2+) indicators like fluo-3. These Single Channel Ca(2+) Fluorescence Transients (SCCaFTs) share some of the characteristics of such elementary events as Ca(2+) sparks and Ca(2+) puffs caused by Ca(2+) release from intracellular stores (due to the opening of ryanodine receptors and IP(3) receptors, respectively). In contrast to intracellular Ca(2+) release events, SCCaFTs can be observed while simultaneously recording the unitary channel currents using patch-clamp techniques to verify the channel openings. Imaging SCCaFTs provides a way to examine localized Ca(2+) handling in the vicinity of a channel with a known Ca(2+) influx, to obtain the Ca(2+) current passing through plasma membrane cation channels in near physiological solutions, to localize Ca(2+) permeable ion channels on the plasma membrane, and to estimate the Ca(2+) currents underlying those elementary events where the Ca(2+) currents cannot be recorded. Here we review studies of these fluorescence transients associated with caffeine-activated channels, L-type Ca(2+) channels, and stretch-activated channels. For the L-type Ca(2+) channel, SCCaFTs have been termed sparklets. In addition, we discuss how SCCaFTs have been used to estimate Ca(2+) currents using the rate of rise of the fluorescence transient as well as the signal mass associated with the total fluorescence increase.
Zou
Hui
H
Department of Physiology and Biomedical Imaging Group, University of Massachusetts Medical School, Worcester, MA 01655, USA. imaging.ionchannels@umassmed.edu
Lifshitz
Lawrence M
LM
Tuft
Richard A
RA
Fogarty
Kevin E
KE
Singer
Joshua J
JJ
D000818:Animals; D002118:Calcium / Q000032:analysis* / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D004553:Electric Conductivity; D005453:Fluorescence
D015220:Calcium Channels; D002118:Calcium