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Mutagenesis and Functional Analysis of Ion Channels Heterologously Expressed in Mammalian Cells
Published on: October 1, 2010
Human potassium channel genes: Molecular cloning and functional expression.
M Ramaswami1, M Gautam, A Kamb
1Department of Entomology & Parasitology, University of California, Berkeley, California 94720, USA.
Molecular and Cellular Neurosciences
|November 17, 2009
Summary
Researchers identified and characterized three human voltage-gated potassium (K+) channels, revealing high conservation across species and distinct functional properties, including varied sensitivity to pharmacological blockers.
Area of Science:
- Molecular biology
- Neuroscience
- Biophysics
Background:
- Voltage-gated potassium (K+) channels are crucial for neuronal excitability.
- Human K+ channels share structural homology with the Drosophila Shaker gene.
- Conserved homologs in rodents suggest ancient origins of these human K+ channel genes.
Purpose of the Study:
- To isolate and characterize three human voltage-gated K+ channels (HuKI, HuKII, HuKIV).
- To determine the nucleotide sequences and functional properties of these channels.
- To compare the pharmacological sensitivities of human K+ channels with their rodent homologs.
Main Methods:
- Complementary DNA (cDNA) isolation and nucleotide sequencing.
- Electrophysiological examination of functional K+ channel products expressed in Xenopus oocytes.
- Assessment of voltage dependence, kinetics, and sensitivity to pharmacological blockers (4-aminopyridine, tetraethylammonium, charybdotoxin).
Main Results:
- Three distinct human K+ channels (HuKI, HuKII, HuKIV) were identified.
- HuKII exhibits rapid inactivation, while HuKI and HuKIV are noninactivating.
- Pharmacological profiles differ: HuKI is sensitive to tetraethylammonium, HuKIV to charybdotoxin, and all are sensitive to 4-aminopyridine.
Conclusions:
- Human voltage-gated K+ channels possess conserved structural features, including membrane-spanning segments and a voltage-sensing S4 segment.
- These channels display significant functional diversity in voltage dependence, kinetics, and drug sensitivity.
- Observed differences in pharmacological sensitivity between human and rat K+ channels highlight species-specific adaptations.
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Ion channels are specialized proteins on the plasma membrane that allow charged ions to pass down their electrochemical gradient. Their main function is to maintain the membrane potential which is critical for cell viability. These channels are either gated or non-gated and can transport more than a thousand ions within milliseconds for the cellular event to occur.
Compared to the gated ion channels, the non-gated channels, also known as leakage or passive channels, have no gating mechanism.
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01:24Non-gated Ion Channels
Ion channels are specialized proteins on the plasma membrane that allow charged ions to pass down their electrochemical gradient. Their main function is to maintain the membrane potential which is critical for cell viability. These channels are either gated or non-gated and can transport more than a thousand ions within milliseconds for the cellular event to occur.
Compared to the gated ion channels, the non-gated channels, also known as leakage or passive channels, have no gating mechanism.
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Voltage-gated ion channels are transmembrane proteins that open and close in response to changes in the membrane potential. They are present on the membranes of all electrically excitable cells such as neurons, heart, and muscle cells.
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