Parvalbumin 3 is an abundant Ca2+ buffer in hair cells.
Ca2+ signaling serves distinct purposes in different parts of a hair cell. The Ca2+ concentration in stereocilia regulates adaptation and, through rapid transduction-channel reclosure, underlies amplification of mechanical signals. In presynaptic active zones, Ca2+ mediates the exocytotic release of afferent neurotransmitter. At efferent synapses, Ca2+ activates the K+ channels that dominate the inhibitory postsynaptic potential. A copious supply of diffusible protein buffer isolates the three signals by restricting the spread of free Ca2+ and limiting the duration of its action. Using cDNA subtraction and a gene expression assay based on in situ hybridization, we detected abundant expression of mRNAs encoding the Ca2+ buffer parvalbumin 3 in bullfrog saccular and chicken cochlear hair cells. We cloned cDNAs encoding this protein from the corresponding inner-ear libraries and raised antisera against recombinant bullfrog parvalbumin 3. Immunohistochemical labeling indicated that parvalbumin 3 is a prominent Ca2+-binding protein in the compact, cylindrical hair cells of the bullfrog's sacculus, and occurs as well in the narrow, peanut-shaped hair cells of that organ. Using quantitative Western blot analysis, we ascertained that the concentration of parvalbumin 3 in saccular hair cells is approximately 3 mM. Parvalbumin 3 is therefore a significant mobile Ca2+ buffer, and perhaps the dominant buffer, in many types of hair cell. Moreover, parvalbumin 3 provides an early marker for developing hair cells in the frog, chicken, and zebrafish.
Heller
Stefan
S
Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10021, USA.
Bell
Andrea M
AM
Denis
Charlotte S
CS
Choe
Yong
Y
Hudspeth
A J
AJ
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002645:Chickens; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004622:Embryo, Mammalian / Q000378:metabolism; D004625:Embryo, Nonmammalian; D005260:Female; D006198:Hair Cells, Auditory / Q000196:embryology / Q000378:metabolism*; D009925:Organ of Corti / Q000378:metabolism; D009994:Osmolar Concentration; D010320:Parvalbumins / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D011892:Rana catesbeiana; D012444:Saccule and Utricle / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology
D002021:Buffers; D018076:DNA, Complementary; D010320:Parvalbumins; D002118:Calcium