Expression and characterization of a canine hippocampal inwardly rectifying K+ current in Xenopus oocytes.
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.
Cui
J
J
Department of Physiology and Biophysics, Health Sciences Center, SUNY, Stony Brook 11794.
Mandel
G
G
DiFrancesco
D
D
Kline
R P
RP
Pennefather
P
P
Datyner
N B
NB
Haspel
H C
HC
Cohen
I S
IS
D000818:Animals; D004285:Dogs; D004558:Electric Stimulation; D005260:Female; D006624:Hippocampus / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D011061:Poly A / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase; D013997:Time Factors; D014982:Xenopus laevis
D012333:RNA, Messenger; D011061:Poly A; D000254:Sodium-Potassium-Exchanging ATPase