Premium
Expression and characterization of a canine hippocampal inwardly rectifying K+ current in Xenopus oocytes.
Author(s) -
Cui J,
Mandel G,
DiFrancesco D,
Kline R P,
Pennefather P,
Datyner N B,
Haspel H C,
Cohen I S
Publication year - 1992
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1992.sp019375
Subject(s) - xenopus , reversal potential , chemistry , voltage clamp , time constant , hippocampal formation , extracellular , biophysics , hyperpolarization (physics) , analytical chemistry (journal) , patch clamp , endocrinology , membrane potential , stereochemistry , biochemistry , biology , electrical engineering , receptor , chromatography , nuclear magnetic resonance spectroscopy , gene , engineering
1. An inwardly rectifying potassium current expressed in Xenopus laevis oocytes injected with canine hippocampal poly(A)+ RNA was investigated with the two‐microelectrode voltage clamp technique. 2. Xenopus oocytes injected with canine hippocampal poly(A)+ RNA expressed a current activated by hyperpolarization. This current contained an instantaneous and a time‐dependent component. Both components were inwardly rectifying and could be blocked by extracellular Cs+ or Ba2+. 3. The expressed current was carried mainly by K+. Its reversal potential measured in different [K+]os could be fitted by the Nernst equation with a slope of ‐50.7 per tenfold change in [K+]o. Extracellular Cl‐ and Na+ made minimal contributions to the current. 4. The activation of the expressed current depended on both voltage and [K+]o. Activation started near EK and the activation curve shifted along the voltage axis in parallel with EK when [K+]o was altered. 5. The activation time constants of the expressed current also depended on both voltage and [K+]o. The voltage dependence of the time constants was bell‐shaped and the peak value was at a potential 30‐50 mV more negative than EK. The voltage dependence of the time constants shifted along the voltage axis when EK was changed. 6. The poly(A)+ RNA extracted from canine hippocampus was fractionated in a 10‐31% linear sucrose gradient. The size of the mRNA required to express the inwardly rectifying current was estimated to be around 4 kb. 7. In conclusion, the expressed current is an inwardly rectifying potassium current. The canine hippocampal mRNA should be an excellent source for expression‐cloning of the inward rectifier channel.