Thanks. We don't really have an answer to your question. Our speculation is that alternative splicing alters the conformational stability of the Na-induced inactive state. We do not think this involves phosphorylation since these data were obtained in excised patches in the absence of phosphorylating agents. However, we have no data to exclude the possibility that differences in basal phosphorylation are involved. Based on the the work of Schulze, Ruknudin, and Lederer (Poster 881), this possibility will be important to investigate.