Characterization of the electrogenic Na+ -K+ pump in bipolar cells isolated from carp retina.
The electrogenic Na+ -K+ pump current (Ip) in carp bipolar cells was investigated under voltage-clamp conditions. The Ip was activated in a concentration-dependent manner by adding external K+ (Ko+) and was completely suppressed with 10(-4) M ouabain (EC50=1.23 mM; Hill coefficient=1.36). The Ip was suppressed in a concentration-dependent manner by ouabain (IC50=1.90 mM; Hill coefficient=0.93). The Ip did not show a distinct voltage dependency either with or without Na(o)+. A large outward shift of the holding current was observed by completely removing Na(o)+. In the presence of Na(o)+, a steady Ip was observed even in the absence of internal Na+ (Na(i)+). These results suggest that continuous Na+ influxes exist across the membrane. When external and internal Na+ was removed, a transient Ip was observed (half decay time (t1/2) was 5.0+/-0.6 s), thus indicating that the transient Ip was activated by the residual Na(i)+. In the absence of Na(o)+, the transient Ip was also observed with lower than 8 mM Na(i)+. The t1/2 depended on Na(i)+. However, a steady Ip was observed with 10 mM Na(i)+ or more. The functional properties of the Ip are discussed.
Zushi
I
I
Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Shimura
M
M
Tamai
M
M
Kakazu
Y
Y
Akaike
N
N
D000818:Animals; D002347:Carps / Q000033:anatomy & histology / Q000378:metabolism*; D016764:Cell Polarity; D004563:Electrochemistry; D004791:Enzyme Inhibitors / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase
D004791:Enzyme Inhibitors; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium