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Sorcin modulates cardiac L‐type Ca2+ current by functional interaction with the α1C subunit in rabbits

We examined the modulation of the cardiac L‐type Ca2+ channel (LTCC) by the regulatory protein sorcin and tested the hypothesis that modulation occurred by direct interaction. Whole‐cell patch‐clamp recordings were made on native rabbit ventricular myocytes and HEK 293 cells expressing cardiac α1C subunits. In ventricular cells, sorcin increased peak current when using either Ca2+ or Ba2+ as charge carriers. In HEK 293 cells, sorcin increased peak current density when using Ba2+ as a charge carrier but not when using Ca2+. In ventricular myocytes, current inactivation (τfast, in ms) was slowed by sorcin with Ca2+ as the charge carrier, whilst in the presence of Ba2+ it was enhanced. In HEK 293 cells, sorcin significantly enhanced τfast, but no significant change was observed with Ba2+. This trend was mimicked by the truncated peptide, sorcin Ca2+‐binding domain, which lacks the N‐terminal domain. These data suggest that sorcin interacts with LTCC via its C‐terminal domain, which alters current magnitude and τfast. These effects appear to be influenced by the prevailing experimental conditions.