In vivo and in vitro phosphorylation of the T lymphocyte type n (Kv1.3) potassium channel.

The major species of voltage-gated potassium channel found on mammalian T lymphocytes is referred to as the type n channel. This potassium channel exhibits unique functional properties which distinguish it from other species of potassium channels, including a potential role in the onset of cellular events associated with T cell activation. As a first step in characterizing specific biochemical properties of the type n channel, we have generated polyclonal antisera against bacterial fusion proteins containing peptide regions unique to the mouse and human type n channel. From membranes of T cell lines derived from both mouse (SAK 8 cell line) and human (Jurkat cell line), the type n channel can be immunoprecipitated following either surface labeling with 125I or metabolic labeling with 32P. The apparent molecular mass of the immunoprecipitated type n channel is approximately 65 kDa, significantly greater than that of the 58-kDa in vitro translated product, and suggestive of post-translational modification events. Phosphoamino acid analysis of the metabolically labeled Jurkat type n channel reveals phosphorylation of serine residues exclusively. In vitro studies also describe the ability of both protein kinase A and protein kinase C to phosphorylate the Jurkat type n channel. The former kinase also appears to phosphorylate a 40-kDa protein which co-immunoprecipitates with the type n channel. These data suggest that direct phosphorylation of the T lymphocyte type n potassium channel or its associated 40-kDa subunit may serve as a means by which channel activity is regulated.