Lack of involvement of protein kinase A phosphorylation in voltage-dependent facilitation of the activity of human cardiac L-type calcium channels.
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 in Xenopus oocytes, 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.
Eisfeld
J
J
Department of Physiology, University of Cologne, Germany.
Mikala
G
G
Schwartz
A
A
Varadi
G
G
Klöckner
U
U
D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005260:Female; D006801:Humans; D015640:Ion Channel Gating; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation; D014982:Xenopus laevis
D015220:Calcium Channels; D000266:Adenylyl Imidodiphosphate; D017868:Cyclic AMP-Dependent Protein Kinases