Expression of Na+,K(+)-ATPase alpha 1 subunit mRNA in the developing rat cochlea.

The distribution of Na+,K(+)-ATPase alpha 1 subunit mRNA was identified using in situ hybridization in the developing rat cochlea. The expression of alpha 1 subunit mRNA in stria vascularis (SV) was observed in all time points studied, 1 to 30 postnatal day (pnd) rats. The adult expression level was attained between 11 to 14 pnd. Surprisingly, alpha 1 subunit mRNA in spiral ligament (SL) and spiral limbus (SLi) was expressed in a more distinct time-dependent manner. At 7 pnd, the alpha 1 subunit mRNA expression was observed initially in the tissues of the SL. At 11 pnd, alpha 1 subunit expression appeared in SLi. Between 11 and 14 pnd, an adult-like pattern of Na+,K(+)-ATPase alpha 1 subunit mRNA expression was attained in the SL and SLi. These data suggest that the expression of Na+,K(+)-ATPase alpha 1 subunit mRNA in these areas are closely related to the development of the rat EP, as its expression in the stria vascularis.