Characterization of the ATP-inhibited K+ current in canine coronary smooth muscle cells |
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Authors: | Xiaoping Xu Kai S Lee |
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Institution: | (1) Cardiovascular Diseases Research, Upjohn Laboratories, 301 Henrietta St., 49007 Kalamazoo, Michigan, MI, USA |
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Abstract: | Intracellular adenosine triphosphate (ATP)-inhibited K+ currents (I
K, ATP
) in canine coronary artery smooth muscle cells were characterized in the wholecell configuration using the suction pipette method. Cells dialysed internally with solutions containing 5 mM ATP (ATPi) showed little detectable whole-cell current at potentials more negative than –30 mV. However, cells dialysed with ATPi-free solutions developed a time- and voltage-independent current which reached a maximum of 132±25 pA at –40 mV about 10 min following patch rupture. After run-up, the current showed little run-down. Concentration-dependent inhibition by ATPi yielded an inhibition constant (K
i of 350 M and a Hill coefficient of 2.3. In ATPi-free solutions, the large current at –40 mV was reduced by glibenclamide with aK
i of 20 nM and a Hill coefficient of 0.95. Conversely, in 1 mM ATPi solutions, the small current at –40 mV was increased by P-1075 from 8±2 pA to 143±33 pA, with a dissociation constant (K
d) of 0.16 M and a Hill coefficient of 1.7. The effect of P-1075 was antagonized by glibenclamide. Maximal current density elicited by either ATPi depletion or external application of the channel opener P-1075 was similar with slope conductances of 81±10 pS/pF and 76±13 pS/pF respectively in the potential range of –90 to –40 mV. External Ca2+ had no effect on this current. Finally, in 1 mM ATPi, 20 and 50 M adenosine increased the current slope conductance by 36±15% and 73±10% respectively between –90 to –40 mV. TheI
K, ATP
although very small in these cells, was extremely effective in causing membrane potential hyperpolarization. |
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Keywords: | ATP-inhibited K current Coronary smooth muscle cells |
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