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J Neurophysiol (May 10, 2006). doi:10.1152/jn.01315.2005
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Submitted on December 14, 2005
Accepted on April 27, 2006

Single channel L-type Ca2+ currents in chicken embryo semicircular canal type I and type II hair cells

Valeria Zampini1, Paolo Valli1, Gianpiero Zucca1, and Sergio Masetto1*

1 Dipartimento di Scienze Fisiologiche-Farmacologiche Cellulari-Molecolari, University of Pavia, Pavia, Italy

* To whom correspondence should be addressed. E-mail: smasetto{at}unipv.it.

Few data are available concerning single Ca channel properties in inner ear hair cells, and particularly none in vestibular type I hair cells. By using the cell-attached configuration of the patch-clamp technique in combination with the semicircular canal crista slice preparation, we determined the elementary properties of voltage-dependent Ca channels in chicken embryo type I and type II hair cells. The pipette solutions included Bay K 8644. With 70 mM Ba2+ in the patch pipette, Ca channel activity appeared as very brief openings at -60 mV. Ca channel properties were found to be similar in type I and type II hair cells; therefore, data were pooled. The mean inward current amplitude was -1.3 pA at -30 mV (± 0.1 SD; n = 16). The average slope conductance was 21 pS (n = 20). With 5 mM Ba2+ in the patch pipette, very brief openings were already detectable at -80 mV. The mean inward current amplitude was -0.7 pA at -40 mV (± 0.2 SD; n = 9). The average slope conductance was 11 pS (n = 9). The mean open time and the open probability increased significantly with depolarisation. Ca channel activity was still present and unaffected when {omega}-agatoxin IVA (2 µM) and {omega}-conotoxin GVIA (3.2 µM) were added to the pipette solution. Our results show that type I and type II hair cells express L-type Ca channels with similar properties. Moreover, they suggest that in vivo Ca2+> influx might occur at membrane voltages more negative than -60 mV.







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