However, these two factors will tend to balance each other out as the development of the endolymphatic potential will increase the MT current to offset www.selleckchem.com/products/azd9291.html the growth in the K+ conductance over the same period (P11–P19). It might be argued that the standing MT current and the depolarization elicited during bundle perfusion with low Ca2+ solution are an artifact of the local perfusion system, perhaps due to damage to the

OHCs or exposure of the basolateral membrane to high K+. This seems unlikely for the following reasons: (1), any nonspecific leak current or depolarization could be abolished with 0.2 mM DHS (Figure 2 and Figure 4) that blocks the MT channel without affecting the voltage-sensitive K+ current; indeed perfusion with DHS was used to define

the nontransducer dependent leak current; (2), OHCs showed a hyperpolarized resting membrane potential (negative to −60 mV) in conditions that turned off the MET current, which indicates the presence of healthy cells; (3), comparison of the fraction of MT current on at rest in rat and gerbil gave the same value (0.46) irrespective check details of whether the low Ca2+ endolymph was accompanied by K+ or Na+, which have similar permeability through the MT channel (Ohmori, 1985); furthermore, membrane potentials in gerbil OHCs (Figure 4) were measured with a Na+-based endolymph; and (4), the standing current, however, relied on the nature of the intracellular mobile Ca2+ buffer and was smaller with EGTA than with BAPTA (Figure 3). The distinction between BAPTA and EGTA largely reflects a difference in the

rate of Ca2+ binding, BAPTA being much faster in lowering the Ca2+ near the internal face of the MT channel (Ricci et al., 1998). This accounts for the difference in the fraction of MT channels open at rest and in resting potential between OHCs (endogenous Ca2+ buffer equivalent to 1 mM BAPTA; Beurg et al., 2010) and IHCs (1 mM EGTA; Johnson et al., 2008). The OHC resting potentials in endolymphatic Ca2+ reported here differ from earlier measurements using other types of preparation and experimental conditions. Most studies on isolated organs of Corti or solitary OHCs have reported resting potentials of −60 to −70 mV (e.g., −57 mV, mafosfamide Housley and Ashmore, 1992; −64 mV, Preyer et al., 1994; −70 mV, Mammano and Ashmore, 1996; −60 mV, Marcotti and Kros, 1999). In those recordings, receptor potentials were only a few millivolts (Preyer et al., 1994) or not reported, suggesting a small standing MT current, a view supported by the more hyperpolarized membrane potential of OHCs obtained on turning off the MET current (Figure 2 and Figure 4) or tip link destruction. The preparation most similar to that used here is the hemi-cochlea (He et al., 2004), which gave a mean OHC resting potential of −57 mV and a maximum receptor potential of 30 mV in the presence of 1.6 mM extracellular Ca2+.