Background: Recently we reported that the dipeptidyl-aminopeptidase-like protein DPP6 serves as a regulatory
f-subunit for cardiac Kv4.3 channels. DPP6 is up-regulated in human failing hearts in which Kv4.3 and the
f-subunit KChIP2 are down-regulated. Here, we provide evidence for the presence of a new member of this protein family, i.e. DPP10, in failing and non-failing human hearts and investigate the role of this putative
f-subunit in regulating transient outward current.
Methods: mRNA was extracted from samples of 5 failing and 5 non-failing human hearts and quantified by realtime PCR. Functional interaction of DPP10 and Kv4.3 was studied in co-expression experiments (Chinese hamster ovary CHO cells) with standard voltage clamp techniques.
Results: Expression level of DPP10 was 85\ub113 fg/ng in failing and 33\ub16 fg/ng total RNA in non-failing hearts (P<0.01), amounting to a 2.6fold reduction. In comparison, DPP6 was up-regulated 1.3fold (P<0.001). After co-expression of Kv4.3 and DPP10 in CHO cells, channel complexes were verified in the plasma membrane by immunostaining, suggesting proper trafficking as with co-expression of Kv4.3 and KChIP2. Expression of Kv4.3 alone failed to yield Ito current, but robust Ito amplitudes were measured after co-expression of Kv4.3 and DPP10, DDP6, or KChIP2. Compared with the conventional co-expression combination of Kv4.3 and KChIP2, kinetics of Ito inactivation were accelerated in Kv4.3 plus DPP10 channels ({tau}fast: 56\ub1 3 ms and 5.9\ub10.4 ms, respectively; P<0.01), however, recovery from inactivation was not affected ({tau}rec: 53\ub1 7 ms vs. 58\ub113 ms). Co-expression of Kv4.3 with KChIP2 plus DPP10 maintained rapid inactivation of Ito ({tau}fast 8\ub11ms), but enhanced recovery kinetics ({tau}rec: 13\ub12 ms, P<0.001). The role of glycosylation for channel kinetics was studied with the glycosylation inhibitor tunicamicin (10 \ub5g/ml; 24h). In the presence of tunicamicin, Ito inactivation and recovery were slowed ({tau}fast 51\ub1 4 ms and {tau}rec: 42\ub13 ms), suggesting importance of glycosylation for channel function. Kinetics were similarly slowed when extracellular domain of DDP10 was deleted ({tau}fast: 48\ub15 ms, {tau}rec: 30\ub1 4 ms).
Conclusion: DPP10, like DPP6 and KChIP2, contributes to regulation of Ito in normal and diseased human hearts
