Differences in molecular mechanisms of K+ clearance in the auditory sensory epithelium of birds and mammals.

Mechanoelectrical transduction in the vertebrate inner ear is a highly conserved mechanism that is dependent on K+ influx into hair cells. Here, we investigated the molecular underpinnings of subsequent K+ recycling in the chicken basilar papilla and compared them with those in the mammalian auditory sensory epithelium. As in mammals, the avian auditory hair cell uses KCNQ4, KCNMA1 and KCNMB1 in its K+ efflux system. Expression of KCNQ1 and KCNE1 suggests an additional efflux apparatus in avian hair cells. Marked differences were observed for K+ clearance. In mammals, KCC3, KCC4, Kir4.1 and CLC-K are present in supporting cells. Of these, only CLC-K is expressed in avian supporting cells. Instead, they possess NKCC1 to move K+ across the membrane. This expression pattern suggests an avian clearance mechanism reminiscent of the well-established K+ uptake apparatus present in inner ear secretory cells. Altogether, tetrapod hair cells show similar mechanisms and supporting cells show distinct molecular underpinnings of K+ recycling.