Lack of Involvement of Protein Kinase A Phosphorylation in Voltage-Dependent Facilitation of the Activity of Human Cardiac L-Type Calcium Channels

• Published in: Biochemical and biophysical research communications Vol. 221; no. 2; pp. 446 - 453
• Main Authors: Eisfeld, Jörg, Mikala, Gabor, Schwartz, Arnold, Varadi, Gyula, Klöckner, Udo
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16.04.1996
• Subjects: Adenylyl Imidodiphosphate - pharmacology; Animals; Calcium Channels - metabolism; Cyclic AMP-Dependent Protein Kinases - metabolism; Female; Humans; Ion Channel Gating; Oocytes - drug effects; Oocytes - metabolism; Phosphorylation; Xenopus laevis
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1006/bbrc.1996.0615

Phosphorylation by protein kinase A is thought to be involved in voltage-dependent facilitation of calcium channels. Here we have shown that the subunit complex of a cloned human cardiac calcium channel, expressed inXenopusoocytes, responds to voltage-dependent facilitation by an approximately 50% increase of the calcium channel peak current. The removal of all protein kinase A consensus sequences by site-directed mutagenesis decreased but did not eliminate the response to prepulse facilitation. Moreover, Rp-cAMP-S, an inhibitor of protein kinase A, could not prevent facilitation of the wild-type calcium channel currents. Similarly, AMP-PNP a nonhydrolyzable analog of ATP, while significantly decreasing the whole-cell current amplitude, failed to reduce the response to double-pulse facilitation. Therefore, we conclude that the voltage-dependent facilitation of cloned calcium channel currents is not due to enhancement of phosphorylation, but probably to some type of voltage-induced conformational change in the channel.