Complete reversal of run-down in rabbit cardiac Ca2+ channels by patch-cramming in Xenopus oocytes; partial reversal by protein kinase A.
The rabbit cardiac Ca2+ channel (alpha1C) expressed in Xenopus oocytes exhibited a complete run-down of ionic currents when cell-attached patches were excised. The alpha1C channel was expressed alone or was coexpressed with the accessory beta2a or beta1b subunit. The catalytic subunit of protein kinase A (PKAc) and MgATP were capable of delaying the run-down of single-channel currents. In 33% of the alpha1C patches, and 26% of the alpha1C+beta2a patches, inclusion of PKAc in the bath solution delayed the run-down for a maximum of 20 min. In experiments where PKAc in the bath was not sufficient to delay the run-down of channel activity, insertion of the patch back into the oocyte (patch-cramming) could restore channel activity. Gating currents were also measured in the alpha1C+beta1b channel and were not subject to any run-down, even after the complete run-down of ionic currents. The results presented here reveal that PKAc is capable of delaying the run-down of currents in a subset of patches. The patch-cramming results suggest that a cytoplasmic factor, in addition to phosphorylation of the channel (by PKAc), may be involved in the maintenance of channel activity.
Costantin
J L
JL
Department of Anesthesiology, UCLA School of Medicine, Los Angeles, CA 90095, USA. Jcostant@ucla.edu
Qin
N
N
Waxham
M N
MN
Birnbaumer
L
L
Stefani
E
E
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000235:genetics* / Q000502:physiology*; D002417:Cattle; D017868:Cyclic AMP-Dependent Protein Kinases / Q000494:pharmacology*; D004229:Dithiothreitol / Q000494:pharmacology; D004553:Electric Conductivity; D005260:Female; D015870:Gene Expression; D015640:Ion Channel Gating / Q000502:physiology; D009206:Myocardium / Q000737:chemistry*; D009865:Oocytes / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D013997:Time Factors; D014981:Xenopus
D015220:Calcium Channels; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; D004229:Dithiothreitol