Ca(2+) currents and voltage responses in Type I and Type II hair cells of the chick embryo semicircular canal.
Type I and Type II hair cells, and Type II hair cells located in different zones of the semicircular canal crista, express different patterns of voltage-dependent K channels, each one specifically shaping the hair cell receptor potential. We report here that, close to hatching, chicken embryo semicircular canal Type I and Type II hair cells express a similar voltage-dependent L-type calcium current (I(Ca)), whose main features are: activation above -60 mV, fast activation kinetics, and scarce inactivation. I(Ca) should be already active at rest in Zone 1 Type II hair cells, whose resting membrane potential was on average slightly less negative than -60 mV. Conversely, I(Ca) would not be active at rest in Type II hair cells from Zone 2 and 3, nor in Type I hair cells, since their resting membrane potential was significantly more negative than -60 mV. However, even small depolarising currents would activate I(Ca) steadily in Zone 2 and 3 Type II hair cells, but not in Type I hair cells because of the robust repolarising action of their specific array of K(+) currents. The implications of the present findings in the afferent discharge are discussed.
Masetto
Sergio
S
Dipartimento di Scienze Fisiologiche-Farmacologiche Cellulari-Molecolari, Sez. di Fisiologia Generale e Biofisica Cellulare, Università di Pavia, Via Forlanini 6, 27100 Pavia, Italy. smasetto@unipv.it
Zampini
Valeria
V
Zucca
Giampiero
G
Valli
Paolo
P
D000818:Animals; D001464:Barium / Q000378:metabolism / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002586:Cesium / Q000494:pharmacology; D002642:Chick Embryo; D018069:Hair Cells, Vestibular / Q000187:drug effects / Q000502:physiology*; D008536:Meglumine / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009532:Nickel / Q000494:pharmacology; D012665:Semicircular Canals / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D020746:Calcium Channels, L-Type; D002104:Cadmium; D002586:Cesium; D001464:Barium; D008536:Meglumine; D009532:Nickel; D002118:Calcium