Photochemical localization of the SEMOTIADIL (cas 116476-13-2) binding region within the cardiac Ca2+ channel α1 subunit. Comparison with the skeletal muscle counterpart

Add time:08/17/2019    Source:sciencedirect.com

We have previously identified the binding region of a new Ca2+ antagonist SEMOTIADIL (cas 116476-13-2) in the skeletal muscle Ca2+ channel. To the same semotiadil derivatives, the cardiac counterpart showed distinct and different binding characteristics: semotiadil and its photoaffinity analog D51-4700 inhibited [3H]PN200-110 binding to cardiac membrane preparations with IC50 values of 13–20 μM, which are 10 times higher than those in skeletal muscle. Hill slopes of the binding inhibition were 0.94–1.0 for the cardiac channels compared to 0.63–0.67 for the skeletal muscle channels. A possible explanation for the difference is that the semotiadil binding site is differently conferred in cardiac and skeletal muscle Ca2+ channels. To reveal this within the primary structure, photoaffinity labeling of cardiac membranes was employed. [3H]D51-4700 was photoincorporated in several polypeptides but only the α1 subunit of the Ca2+ channel was photolabeled in a specific manner. Antibody mapping of the [3H]D51-4700-labeled α1 subunit with several anti-peptide antibodies revealed that the labeled site was located solely in a peptide fragment between Cys1461 and Lys1529. This region encompasses the labeled site of skeletal muscle, but contains several non-identical amino acid residues, which may participate in expressing different binding characteristics between the two muscle type Ca2+ channels.

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