Figure 4.

Effects of PLM and its mutants on peak I_Ca in cultured KO myocytes. A. Schematic representation of WT PLM (both dog and rat) and dog PLM mutants. The structure of dog PLM (PLM) is shown to consist of an extracellular NH₂-terminal domain (black), a single-span transmembrane domain (blue), and cytoplasmic COOH-terminal domain (purple). The signature PFXYD sequence is shown in gold at the NH₂-terminus, and the 4 potential phosphorylation sites (Ser⁶², Ser⁶³, Ser⁶⁸ and Thr⁶⁹) are represented by pink boxes at the COOH-terminus. The 6 amino acid differences between dog PLM and rat PLM (ALIGN) are shown. Mouse PLM is identical to rat PLM except that Thr⁶⁹ is replaced by Ser⁶⁹ (not shown). All PLM mutants were constructed on the dog PLM backbone. Shown are representations of COOH-terminal deletion mutant (TM43), Ser⁶⁸ substitution mutants (S68A and S68E), and ALL5 mutant in which the signature PFXYD motif is changed to Ala (shown as gold to red). Ser to Ala mutation is shown as pink to black, whereas Ser to Glu mutation is shown as pink to yellow. B. Summary of peak I_Ca (at −10 mV) measured in adenovirus-infected KO myocytes followed by culture for 24 hours, both in the absence (open bars) and presence (filled bars) of 1 µM isoproterenol. *p<0.03, KO-GFP vs. KO-PLM or KO-PLM mutants at baseline; #p<0.05, KO-GFP vs. KO-PLM or KO-PLM mutants in the presence of 1 µM isoproterenol; $p<0.04, KO-PLM vs. KO-ALL5 at baseline, and KO-PLM vs. KO-ALL5 or KO-S68E or KO-S68A in the presence of 1 µM isoproterenol. C. Summary of τ_inact (at −10 mV) measured in adenovirus-infected KO myocytes followed by culture for 24 hours, both in the absence (open bars) and presence (filled bars) of 1 µM isoproterenol. *p<0.035, KO-GFP vs. KO-PLM or KO-PLM mutants at baseline; #p<0.0045, KO-GFP vs. KO-PLM or KO-PLM mutants in the presence of 1 µM isoproterenol.