Complete reversal of run-down in rabbit cardiac Ca2+ channels by patch-cramming in Xenopus oocytes; partial reversal by protein kinase A |
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| Authors: | J.L. Costantin Ning Qin M. Neal Waxham Lutz Birnbaumer Enrico Stefani |
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| Affiliation: | (1) Department of Anesthesiology, UCLA School of Medicine, Los Angeles, CA 90095, USA, US;(2) Department of Neurobiology and Anatomy, University of Texas Health Science Center, Houston, TX 77054,;(3) Department of Neurology, UCLA School of Medicine, Los Angeles, CA 90095-1769, USA e-mail: Jcostant@ucla.edu Fax: +1-310-2069819, US |
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| Abstract: | The rabbit cardiac Ca2+ channel (α1C) expressed in Xenopus oocytes exhibited a complete run-down of ionic currents when cell-attached patches were excised. The α1C channel was expressed alone or was coexpressed with the accessory β2a or β1b 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 α1C patches, and 26% of the α1C+β2a 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 α1C+β1b 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. Received: 29 October 1998 / Accepted: 4 January 1999 |
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| Keywords: | Calcium channel Cytoplasm Patch clamp Patch-cramming Protein kinase A Run-down Xenopus oocyte |
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