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

摘要

class="enumerated" style="list-style-type:decimal">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.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 μM ouabain abolished this current. Thus, this K⁺-induced and ouabain-sensitive current was considered to be the Na⁺-K⁺ pump current.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.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).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⁺.Ouabain inhibited the Na⁺-K⁺ pump current in a dose-dependent manner with a Kd of 0.35 ± 0.03 μM and an nH of 1.2 ± 0.1 (n = 6–8).The Na⁺-K⁺ pump current increased as temperature increased. The temperature coefficient (Q10; 26–36 °C) was 1.87 (n = 9).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.