DISTRIBUTION OF CA2-ACTIVATED K+ CHANNEL ISOFORMS ALONG THE TONOTOPICGRADIENT OF THE CHICKENS COCHLEA()

In some cochleae, the number and kinetic properties of Ca2+-activated K+ (K-Ca) channels partly determine the characteristic frequency of ea ch hair cell and thus help establish a tonotopic map. In the chicken's basilar papilla, we found numerous isoforms of K-Ca channels generate d by alternative mRNA splicing at seven sites in a single gene, cSlo. In situ polymerase chain reactions demonstrated cSlo expression in hai r cells and revealed differential distributions of K-Ca channel isofor ms along the basilar papilla. Analysis of single hair cells by the rev erse transcription polymerase chain reaction confirmed the differentia l expression of channel variants. Heterologously expressed cSlo varian ts differed in their sensitivities to Ca2+ and voltage, suggesting tha t the distinct spatial distributions of cSlo variants help determine t he tonotopic map.