Selective inhibition of a slow-inactivating voltage-dependent K+ channel in rat PC12 cells by hypoxia.
1. Electrophysiological (single-channel patch clamp) and molecular biological experiments (reverse transcriptase-polymerase chain reaction) were performed to attempt to identify the O2-sensitive K+ channel in rat phaeochromocytoma (PC12) cells. 2. Four types of K+ channels were recorded in PC12 cells: a small-conductance K+ channel (14 pS), a calcium-activated K+ channel (KCa; 102 pS) and two K+ channels with similar conductance (20 pS). These last two channels differed in their time-dependent inactivation: one was a slow-inactivating channel, while the other belonged to the family of fast transient K+ channels. 3. The slow-inactivating 20 pS K+ channel was inhibited by hypoxia. Exposure to hypoxia produced a 50% reduction in channel activity (number of active channels in the patch x open probability). Hypoxia had no effect on the 20 pS transient K+ channels, whereas reduced O2 stimulated the KCa channels. 4. The genes encoding the alpha-subunits of slow-inactivating K+ channels for two members of the Shaker subfamily of K+ channels (Kv1.2 and Kv1.3) together with the Kv2.1, Kv3.1 and Kv3.2 channel genes were identified in PC12 cells. 5. The expression of the Shaker Kv1.2, but none of the other K+ channel genes, increased in cells exposed to prolonged hypoxia (18 h). The same cells were more responsive to a subsequent exposure to hypoxia (35% inhibition of K+ current measured in whole-cell voltage clamp) compared with the cells maintained in normoxia (19% inhibition). 6. These results indicate that the O2-sensitive K+ channel in PC12 cells is a 20 pS slow-inactivating K+ channel that is upregulated by hypoxia. This channel appears to belong to the Shaker subfamily of voltage-gated K+ channels.
Conforti
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Department of Molecular and Cellular Physiology, College of Medicine, University of Cincinnati, OH 45267-0576, USA. conforl@ucbeh.san.uc.edu
Millhorn
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D000310:Adrenal Gland Neoplasms; D000818:Animals; D015687:Cell Hypoxia; D004553:Electric Conductivity; D015870:Gene Expression; D008564:Membrane Potentials; D010100:Oxygen / Q000494:pharmacology; D016716:PC12 Cells; D018408:Patch-Clamp Techniques; D010673:Pheochromocytoma; D016133:Polymerase Chain Reaction; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000096:biosynthesis / Q000502:physiology*; D051381:Rats
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D010100:Oxygen