Contribution of the plasmalemma to Ca2+ homeostasis in hair cells.
Calcium influx through transduction channels and efflux via plasmalemmal Ca(2+)-ATPases (PMCAs) are known to contribute to calcium homeostasis and modulate sensory transduction in vertebrate hair cells. To examine the relative contributions of apical and basolateral pathways, we analyzed the calcium dynamics in solitary ciliated and deciliated guinea pig type I and type II vestibular hair cells. Whole-cell patch-clamp recordings demonstrated that these cells had resting potentials near -70 mV and could be depolarized by 10-20 mV by superfusion with high potassium. Fura-2 measurements indicated that ciliated type II cells and deciliated cells of either type had low basal [Ca(2+)](i), near approximately 90 nm, and superfusion with high potassium led to transient calcium increases that were diminished in the presence of Ca(2+) channel blockers. In contrast, measurements of type I ciliated cells, hair cells with large calyceal afferents, were associated with a higher basal [Ca(2+)](i) of approximately 170 nm. High-potassium superfusion of these cells induced a paradoxical decrease in [Ca(2+)](i) that was augmented in the presence of Ca(2+) channel blockers. Optical localization of dihydropyridine binding to the kinocilium suggests that they contain L-type calcium channels, and as a result apical calcium influx includes a contribution from voltage-dependent ion channels in addition to entry via transduction channels localized to the stereocilia. Eosin block of PMCA significantly altered both [Ca(2+)](i) baseline and transient responses only in ciliated cells suggesting that, in agreement with immunohistochemical studies, PMCA is primarily localized to the bundles.
Boyer
C
C
Institut National de la Santé et de la Recherche Médicale U-432, Université Montpellier II, 34095 Montpellier cedex 05, France. cboyer@uic.edu
Art
J J
JJ
Dechesne
C J
CJ
Lehouelleur
J
J
Vautrin
J
J
Sans
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002469:Cell Separation; D002923:Cilia / Q000378:metabolism / Q000648:ultrastructure; D004095:Dihydropyridines / Q000378:metabolism; D004801:Eosine Yellowish-(YS) / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000494:pharmacology; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology*; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D015388:Organelles / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004095:Dihydropyridines; D005456:Fluorescent Dyes; C038806:1,4-dihydropyridine; D000252:Calcium-Transporting ATPases; D011188:Potassium; D002118:Calcium; D004801:Eosine Yellowish-(YS)