Sodium-potassium pump current in smooth muscle cells from mesenteric resistance arteries of the guinea-pig.
1. The Na+-K+ pump current was studied in smooth muscle cells from mesenteric resistance arteries of guinea-pigs by the use of the perforated patch-clamp technique in the presence of blockers for various ion channels and exchangers. 2. When the Na+ concentration in the pipette solution ([Na+]i) was 50 mM, an increase in the extracellular K+ concentration ([K+]o) from 0 to 10 mM caused an outward current. Both the removal of K+ from the bath solution and the application of 10 microM ouabain abolished this current. Thus, this K+-induced and ouabain-sensitive current was considered to be the Na+-K+ pump current. 3. The amplitude of the Na+-K+ pump current increased as the membrane potential was made more positive until around 0 mV, while the amplitude saturated at more positive potentials than 0 mV. 4. An increase in [K+]o or [Na+]i amplified the Na+-K+ pump current. For [K+]o, the binding constant (Kd) was 1.6+/-0.3 mM and the Hill coefficient (nH) was 1.1+/-0.2 (n = 6). For [Na+]i, Kd was 22+/-5 mM and nH was 1.7+/-0.5 (n = 4-19). 5. The presence of various monovalent cations other than Na+ in the bath solution also evoked the Na+-K+ pump current. The order of potency was K+ >= Rb+ > Cs+ >> Li+. 6. Ouabain inhibited the Na+-K+ pump current in a dose-dependent manner with a Kd of 0.35+/-0.03 microM and an nH of 1.2+/-0.1 (n = 6-8). 7. The Na+-K+ pump current increased as temperature increased. The temperature coefficient (Q10; 26-36 C) was 1.87 (n = 9). 8. In summary the present study characterized for the first time the Na+-K+ pump current in vascular smooth muscle cells by the use of the voltage-clamp method. The use of this method should provide essential information for Na+,K+-ATPase-mediated changes in the cell functions of vascular smooth muscle cells.
Nakamura
Y
Y
Second Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Ohya
Y
Y
Abe
I
I
Fujishima
M
M
D000818:Animals; D002414:Cations, Monovalent / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D008638:Mesenteric Arteries / Q000201:enzymology / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000201:enzymology / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013816:Thermodynamics; D014655:Vascular Resistance
D002414:Cations, Monovalent; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium