K⁺-Induced Dilation of Hamster Cremasteric Arterioles Involves Both the Na⁺/K⁺-ATPase and Inward-Rectifier K⁺Channels

Abstract

Objective:The mechanism by which elevated extracellular potassium ion concentration ([K⁺]_o) causes dilation of skeletal muscle arterioles was evaluated. Methods:Arterioles (n= 111) were hand-dissected from hamster cremaster muscles, cannulated with glass micropipettes and pressurized to 80 cm H₂O for in vitrostudy. The vessels were superfused with physiological salt solution containing 5 mM KCl, which could be rapidly switched to test solutions containing elevated [K⁺]_oand/or inhibitors. The authors measured arteriolar diameter with a computer-based diameter tracking system, vascular smooth muscle cell membrane potential with sharp micropipettes filled with 200 mM KCl, and changes in intracellular Ca²⁺concentration ([Ca²⁺]_i) with Fura 2. Membrane currents and potentials also were measured in enzymatically isolated arteriolar muscle cells using patch clamp techniques. The role played by inward rectifier K⁺(K_IR) channels was tested using Ba²⁺as an inhibitor. Ouabain and substitution of extracellular Na⁺with Li⁺were used to examine the function of the Na⁺/K⁺ATPase. Results:Elevation of [K⁺]_ofrom 5 mM up to 20 mM caused transient dilation of isolated arterioles (27 ± 1 μm peak dilation when [K⁺]_owas elevated from 5 to 20 mM, n= 105, p< .05). This dilation was preceded by transient membrane hyperpolarization (10 ± 1 mV, n= 23, p< .05) and by a fall in [Ca²⁺]_ias indexed by a decrease in the Fura 2 fluorescence ratio of 22 ± 5% (n= 4, p< .05). Ba²⁺(50 or 100 μM) attenuated the peak dilation (40 ± 8% inhibition, n= 22) and hyperpolarization (31 ± 12% inhibition, n= 7, p< .05) and decreased the duration of responses by 37 ± 11% (n= 20, p< 0.05). Both ouabain (1 mM or 100 μM) and replacement of Na⁺with Li⁺essentially abolished both the hyperpolarization and vasodilation. Conclusions:Elevated [K⁺]_ocauses transient vasodilation of skeletal muscle arterioles that appears to be an intrinsic property of the arterioles. The results suggest that K⁺-induced dilation involves activation of both the Na⁺/K⁺ATPase and K_IRchannels, leading to membrane hyperpolarization, a fall in [Ca²⁺]_i, and culminating in vasodilation. The Na⁺/K⁺ATPase appears to play the major role and is largely responsible for the transient nature of the response to elevated [K⁺]_o, whereas K_IRchannels primarily affect the duration and kinetics of the response. Microcirculation(2004) 11,279–293. doi:10.1080/10739680490425985

• arterioles
• ATP-sensitive potassium channels
• barium ions
• calcium ions
• Fura 2
• inward-rectifier potassium channels
• membrane potential
• Na⁺/K⁺ATPase
• ouabain
• potassium channels
• potassium ions
• skeletal muscle
• vasodilation