Rubidium and sodium permeability of the ATP-sensitive K+ channel in single rat pancreatic beta-cells.
1. The patch-clamp method has been used to study the selectivity of single ATP-sensitive potassium channels in excised membrane patches from dissociated rat pancreatic beta-cells. 2. In symmetrical K+ concentrations the current-voltage relation of this channel showed slight inward rectification. The...
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| Format: | Journal article |
| Language: | English |
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1989
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| _version_ | 1797064852926103552 |
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| author | Ashcroft, F Kakei, M Kelly, R |
| author_facet | Ashcroft, F Kakei, M Kelly, R |
| author_sort | Ashcroft, F |
| collection | OXFORD |
| description | 1. The patch-clamp method has been used to study the selectivity of single ATP-sensitive potassium channels in excised membrane patches from dissociated rat pancreatic beta-cells. 2. In symmetrical K+ concentrations the current-voltage relation of this channel showed slight inward rectification. The K+ permeability coefficient was 1.05 x 10(-13) cm3/s ([K+]o = 140 mM; 20 degrees C) in the inside-out patch and somewhat smaller when measured under the same conditions in the outside-out configuration (0.86 x 10(-13) cm3/s). 3. When intracellular Rb+ replaced K+, inward K+ currents were unaffected but the outward currents carried by Rb+ were substantially smaller. The extent of the reduction in the outward currents depended on the internal Rb+/K+ ratio and increased as [Rb+]i was raised. Both inward and outward Rb+ currents were blocked by 1 mM-ATP. No currents were measurable in symmetrical 140 mM-Rb+ solutions. 4. With 140 mM [K+]o and 140 mM [Rb+]i the single-channel current-voltage relation reversed at +8 mV and the potential at which the variance of the ATP-sensitive current was least was shifted by 6 mV to more positive potentials. These data suggest a PRb/PK ratio of around 0.7. 5. Outward Rb+ currents were reduced at all potentials in inside-out patches exposed to 107 mM-Rb+ solution intracellularly and 5 mM-K+ externally. 6. Partial replacement of external K+ with Rb+ substantially reduced the inward currents recorded from outside-out patches and also decreased outward K+ currents. 7. In outside-out patches, the addition of 1 mM-Rb+ to the external solution produced a block of inward K+ currents that initially increased and then decreased again with hyperpolarization. This suggests that the Rb+ block of K+ currents is voltage dependent and that Rb+ acts as a permeant blocker of K+ currents. 8. The sodium permeability of the channel, relative to that of potassium, was 0.39 for internal Na+ and 0.007 for external Na+ ions. 9. We conclude that Rb+ serves as an acceptable tracer for K+ in efflux studies when changes in K+ flux through ATP-sensitive K+ channels are of interest but that the magnitude of such fluxes will be considerably underestimated. |
| first_indexed | 2024-03-06T21:20:18Z |
| format | Journal article |
| id | oxford-uuid:413af3cb-33a2-4a31-80a8-e4d7d59e3c9f |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T21:20:18Z |
| publishDate | 1989 |
| record_format | dspace |
| spelling | oxford-uuid:413af3cb-33a2-4a31-80a8-e4d7d59e3c9f2022-03-26T14:42:22ZRubidium and sodium permeability of the ATP-sensitive K+ channel in single rat pancreatic beta-cells.Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:413af3cb-33a2-4a31-80a8-e4d7d59e3c9fEnglishSymplectic Elements at Oxford1989Ashcroft, FKakei, MKelly, R1. The patch-clamp method has been used to study the selectivity of single ATP-sensitive potassium channels in excised membrane patches from dissociated rat pancreatic beta-cells. 2. In symmetrical K+ concentrations the current-voltage relation of this channel showed slight inward rectification. The K+ permeability coefficient was 1.05 x 10(-13) cm3/s ([K+]o = 140 mM; 20 degrees C) in the inside-out patch and somewhat smaller when measured under the same conditions in the outside-out configuration (0.86 x 10(-13) cm3/s). 3. When intracellular Rb+ replaced K+, inward K+ currents were unaffected but the outward currents carried by Rb+ were substantially smaller. The extent of the reduction in the outward currents depended on the internal Rb+/K+ ratio and increased as [Rb+]i was raised. Both inward and outward Rb+ currents were blocked by 1 mM-ATP. No currents were measurable in symmetrical 140 mM-Rb+ solutions. 4. With 140 mM [K+]o and 140 mM [Rb+]i the single-channel current-voltage relation reversed at +8 mV and the potential at which the variance of the ATP-sensitive current was least was shifted by 6 mV to more positive potentials. These data suggest a PRb/PK ratio of around 0.7. 5. Outward Rb+ currents were reduced at all potentials in inside-out patches exposed to 107 mM-Rb+ solution intracellularly and 5 mM-K+ externally. 6. Partial replacement of external K+ with Rb+ substantially reduced the inward currents recorded from outside-out patches and also decreased outward K+ currents. 7. In outside-out patches, the addition of 1 mM-Rb+ to the external solution produced a block of inward K+ currents that initially increased and then decreased again with hyperpolarization. This suggests that the Rb+ block of K+ currents is voltage dependent and that Rb+ acts as a permeant blocker of K+ currents. 8. The sodium permeability of the channel, relative to that of potassium, was 0.39 for internal Na+ and 0.007 for external Na+ ions. 9. We conclude that Rb+ serves as an acceptable tracer for K+ in efflux studies when changes in K+ flux through ATP-sensitive K+ channels are of interest but that the magnitude of such fluxes will be considerably underestimated. |
| spellingShingle | Ashcroft, F Kakei, M Kelly, R Rubidium and sodium permeability of the ATP-sensitive K+ channel in single rat pancreatic beta-cells. |
| title | Rubidium and sodium permeability of the ATP-sensitive K+ channel in single rat pancreatic beta-cells. |
| title_full | Rubidium and sodium permeability of the ATP-sensitive K+ channel in single rat pancreatic beta-cells. |
| title_fullStr | Rubidium and sodium permeability of the ATP-sensitive K+ channel in single rat pancreatic beta-cells. |
| title_full_unstemmed | Rubidium and sodium permeability of the ATP-sensitive K+ channel in single rat pancreatic beta-cells. |
| title_short | Rubidium and sodium permeability of the ATP-sensitive K+ channel in single rat pancreatic beta-cells. |
| title_sort | rubidium and sodium permeability of the atp sensitive k channel in single rat pancreatic beta cells |
| work_keys_str_mv | AT ashcroftf rubidiumandsodiumpermeabilityoftheatpsensitivekchannelinsingleratpancreaticbetacells AT kakeim rubidiumandsodiumpermeabilityoftheatpsensitivekchannelinsingleratpancreaticbetacells AT kellyr rubidiumandsodiumpermeabilityoftheatpsensitivekchannelinsingleratpancreaticbetacells |