Lighting up the senses: FM1-43 loading of sensory cells through nonselective ion channels.
We describe a novel mechanism for vital fluorescent dye entry into sensory cells and neurons: permeation through ion channels. In addition to the slow conventional uptake of styryl dyes by endocytosis, small styryl dyes such as FM1-43 rapidly and specifically label hair cells in the inner ear by entering through open mechanotransduction channels. This labeling can be blocked by pharmacological or mechanical closing of the channels. This phenomenon is not limited to hair cell transduction channels, because human embryonic kidney 293T cells expressing the vanilloid receptor (TRPV1) or a purinergic receptor (P2X2) rapidly take up FM1-43 when those receptor channels are opened and not when they are pharmacologically blocked. This channel permeation mechanism can also be used to label many sensory cell types in vivo. A single subcutaneous injection of FM1-43 (3 mg/kg body weight) in mice brightly labels hair cells, Merkel cells, muscle spindles, taste buds, enteric neurons, and primary sensory neurons within the cranial and dorsal root ganglia, persisting for several weeks. The pattern of labeling is specific; nonsensory cells and neurons remain unlabeled. The labeling of the sensory neurons requires dye entry through the sensory terminal, consistent with permeation through the sensory channels. This suggests that organic cationic dyes are able to pass through a number of different sensory channels. The bright and specific labeling with styryl dyes provides a novel way to study sensory cells and neurons in vivo and in vitro, and it offers new opportunities for visually assaying sensory channel function.
Meyers
Jason R
JR
Neuroscience Graduate Program, University of Virginia, Charlottesville, Virginia 22908, USA. jmeyers@virginia.edu
MacDonald
Richard B
RB
Duggan
Anne
A
Lenzi
David
D
Standaert
David G
DG
Corwin
Jeffrey T
JT
Corey
David P
DP
D000818:Animals; D002460:Cell Line; D003051:Cochlea / Q000166:cytology / Q000378:metabolism; D015194:Diffusion Chambers, Culture; D004705:Endocytosis / Q000502:physiology; D006199:Hair Cells, Auditory, Inner / Q000378:metabolism*; D006801:Humans; D007279:Injections, Subcutaneous; D007473:Ion Channels / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D008465:Mechanoreceptors / Q000378:metabolism; D051379:Mice; D008809:Mice, Inbred C3H; D018613:Microscopy, Confocal / Q000379:methods; D009475:Neurons, Afferent / Q000378:metabolism*; D011726:Pyridinium Compounds / Q000008:administration & dosage / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000008:administration & dosage / Q000378:metabolism*; D011892:Rana catesbeiana; D011955:Receptors, Drug / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058476:Receptors, Purinergic P2X2; D012444:Saccule and Utricle / Q000166:cytology / Q000378:metabolism; D050916:TRPV Cation Channels; D014276:Trigeminal Nerve / Q000378:metabolism / Q000502:physiology
C073804:FM1 43; D007473:Ion Channels; C546401:P2RX2 protein, human; C546402:P2rx2 protein, mouse; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D011955:Receptors, Drug; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D050916:TRPV Cation Channels; C494484:TRPV1 receptor