Cell-surface expression of hCNT3 and mutants. Oocytes injected with RNA transcripts encoding E343Q, E343C, or E343D (A), E519Q, E519C, or E519D (B), or wild-type hCNT3 (A and B) and control water-injected oocytes (A and B) were assayed for the presence of plasma membrane recombinant protein by immunoblotting. Staining intensities relative to wild-type hCNT3 (100- and 86-kDa immunostained bands combined) were 0.77, 0.83, and 1.08 for E343Q, E343D, and E343C, respectively, and 0.98, 0.71, and 1.15 for E519Q, E519D, and E519C, respectively.