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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
-agatoxin IVA (2 µM) and
-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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