Sodium-potassium pump current in smooth muscle cells from mesenteric resistance arteries of the guinea-pig

1. 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 el;changers. 2. When the Na+ concentration in the pipette solution ([Na+](1)) was 50 mM, an increase in the extracellular K+ concentration ([K+](0)) from 0 to 10 mM. caused an outward current. Both the removal of K+ from the bath solution and the application of 10 mu M 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+](0) or [Na+](1) amplified the Na+-K+ pump current. For [K+](0), the binding constant (K-d), was 1.6 +/- 0.3 mM and the Hill coefficient (n(H)) was 1.1 +/- 0.2 ( n = 6). For [Na+](1) K-d was 22 +/- 5 mM and n(H) was 1.7 +/- 0.5 (n = 4-19). 5. The presence of various monovalent cations other than Na+ in the hath solution also evoked the Na+-K+ pump current. The order of potency was K+ greater than or equal to Rb+ > Cs+ >> Li+. 6. Ouabain inhibited the Na+-K+ pump current in a dose-dependent manner with a K-d of 0.35 +/- 0.03 mu M and an n(H) of 1.2 +/- 0.1 (n = 6-8). 7. The Na+-K+ pump current increased as temperature increased. The temperature coefficient (Q(10); 26-36 degrees 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.