Functional effects of a monoclonal antibody on mechanoelectrical transduction in outer hair cells

Tonic mechanosensitivity of outer hair cells after loss of tip links

“…Together with the upper-attachment region of the tip link, the contact region shows the greatest immunological labelling for calmodulin , suggesting this is a distinctly Ca 2+ -active region. According to dynamicrange data, for both isolated Schulte et al, 2002) and in situ (He et al, 2004) OHCs, the observed tilt (2.9 ± 1.6°) in the excitatory direction is consistent in magnitude and direction with the angular deflection required to open channels. Conversely, it is sufficiently small to enable channel closure for the inhibitory deflections used in these experiments (200-500 nm).…”

“…Indeed this has always been the case in our isolated cell preparation: (i) probability of channel opening is describable by a second-order Boltzmann function with 10-90% activation of transducer current of between 150 and 300 nm Schulte et al, 2002; and these experiments, not illustrated), and (ii) saturation current versus voltage curve describable by a simple, one-energy barrier model, with zero reversal potential (Schulte et al, 2002; and these experiments, not illustrated). Our acceptance of data from a proportion of normal functioning channels is based on the still common assumption (e.g., Holton and Hudspeth, 1986;van Netten et al, 2003), based on single-channel data (Crawford et al, 1991;Géléoc et al, 1997;Ricci et al, 2003), that the whole-cell current is simply the sum of unitary currents from identical transducer channels.…”

“…All methods, except those for increasing intracellular Ca 2+ concentration, have been described in detail in Preyer et al (1995; Meyer et al (1998) and Schulte et al (2002).…”

“…In earlier publications from our laboratory (Preyer et al, 1995Meyer et al, 1998;Schulte et al, 2002) we discussed the relatively small size of the receptor currents (e.g., range 10-110 pA and mean 40 pA, as given in Meyer et al (1998)) for OHCs isolated from the adult guinea-pig cochlea compared with those from bullfrog, turtle or neonatal mouse hair cells, where the currents can be as much as several hundred picoamperes (e.g., Corey and Hudspeth, 1983;Crawford et al, 1991;Kros et al, 1992;Rüsch et al, 1994). At that time, our reports were the only ones for OHCs from the functionally mature mammalian cochlea (appearing in refereed journals).…”

“…Transducer channels were blocked by applying the aminoglycoside antibiotic dihydrostreptomycin (DHSM, 100 lM; Kroese et al, 1989;Kimitsuki and Ohmori, 1993;Meyer et al, 1998) or amiloride (300 lM;Rüsch et al, 1994;Meyer et al, 1998;Schulte et al, 2002). The calcium-specific chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N 0 ,N 0 -tetra-acetic acid (BAPTA, 5 mM) was used to break tip links (Assad et al, 1991;Meyer et al, 1998).…”