Unique 5′-End of a Na⁺-K⁺-2C1⁻- Cotransporter-Like mRNA Expressed in Rat Skeletal Muscle

Abstract

Functional evidence presented by others indicates that rat slow-twitch skeletal muscle lacks typical Na⁺-K⁺-2Cl⁻ cotransporter activity, as determined by loop diuretic-sensitive potassium transport. This report presents a unique 5′ mRNA sequence of a Na⁺-K⁺-2Cl⁻ cotransporter-like molecule expressed in the rat soleus muscle and the deduced N-terminus of the protein. In addition to its unique 5′ mRNA sequence, the coding region of the N-terminus is quite short compared with other known Na⁺-K⁺-2Cl⁻cotransporters. Nonetheless, the mRNA possesses conserved cotransporter-like membrane spanning domains, though one domains corresponding to a reported exon is divergent. Therefore, it appears that skeletal muscle does express a Na^C-K⁺-2Cl⁻ cotransporter-like mRNA that may code for a protein with atypical Na⁺-K⁺-2Cl⁻ cotransporter properties.

Key Words:

• Na⁺-K⁺-2Cl⁻ cotransporter
• osmoregulation
• skeletal muscle
• slow-twitch muscle