The Calcium Dependence of Avian (Gallus) Hair Cell AChRs cochlea

GI-JUNG I; LIPOVSEK M; KATZ E; ELGOYHEN AB; FUCHS PA

Baltimore USA

Congreso; 34th Midwinter Meeting, Association for Research in Otolaryngology; 2011

The Calcium Dependence of Avian (Gallus) Hair Cell AChRs Gi-jung Im1,2, Marcela Lipovsek3, Katz E, Ana Belen Elgoyhen3 and Paul Albert Fuchs1, Department of Otolaryngology-Head and Neck Surgery, the Johns Hopkins School of Medicine.2Department of Otolaryngology-Head and Neck Surgery, Korea University College of Medicine. 3INGEBI, Buenos Aires, Argentina.  Mammalian and avian hair cells employ heteromeric  alpha9 and alpha10 AChRs to mediate efferent inhibition of auditory hair cells.  Heterologous expression in Xenopus oocytes has shown that while mammalian (rat) a9a10 AChRs have a substantial permeability to calcium, that of avian (chicken) AChRs is significantly lower (Lipovsek et al., ARO 2009).   Here we examine the response to ACh of native AChRs in chicken hair cells.  Whole-cell, giga-ohm seal intracellular recordings were made on ‘short’ (abneural) hair cells approximately at the midpoint of the 4 mm long basilar papilla (chicken auditory organ) from late-stage embryos (E17-20) using intracellular cesium/BAPTA and extracellular apamin to minimize SK current.  Puff application of ACh (1 mM, 200 ms) elicited inward currents at negative membrane potentials that reversed near 0 mV.   The reversal potential was determined using ‘ramp’ voltage commands from -100 to +40 mV, 200 ms duration, designed to coincide with the steady maximal response to ACh.   This measurement was carried in 5-10 hair cells in each of 1, 3, 10 and 30 mM calcium saline.  The ACh-evoked current was largest in 3 mM calcium, and displayed outward rectification that was more pronounced in higher calcium concentrations.  There was no significant difference in reversal potential as a function of calcium concentration.  Thus, like cloned avian a9a10, the native chicken hair cell AChR appears to have a low permeability to calciumSupported by NIDCD R01DC001508 and by the National Research Foundation of Korea Grant funded by the Korean Government MEST, Basic Research Promotion Fund (NRF-2010-013-E00015).