K⁺‐induced hyperpolarization in rat mesenteric artery: identification, localization and role of Na⁺/K⁺‐ATPases

Abstract

Mechanisms underlying K+‐induced hyperpolarizations in the presence and absence of phenylephrine were investigated in endothelium‐denuded rat mesenteric arteries (for all mean values, n=4). Myocyte resting membrane potential (m.p.) was −58.8±0.8 mV. Application of 5 mM KCl produced similar hyperpolarizations in the absence (17.6±0.7 mV) or presence (15.8±1.0 mV) of 500 nM ouabain. In the presence of ouabain +30 μM barium, hyperpolarization to 5 mM KCl was essentially abolished. In the presence of 10 μM phenylephrine (m.p. −33.7±3 mV), repolarization to 5 mM KCl did not occur in the presence or absence of 4‐aminopyridine but was restored (−26.9±1.8 mV) on addition of iberiotoxin (100 nM). Under these conditions the K+‐induced repolarization was insensitive to barium (30 μM) but abolished by 500 nM ouabain alone. In the presence of phenylephrine + iberiotoxin the hyperpolarization to 5 mM K+ was inhibited in the additional presence of 300 nM levcromakalim, an action which was reversed by 10 μM glibenclamide. RT–PCR, Western blotting and immunohistochemical techniques collectively showed the presence of α1‐, α2‐ and α3‐subunits of Na+/K+‐ATPase in the myocytes. In K+‐free solution, re‐introduction of K+ (to 4.6 mM) hyperpolarized myocytes by 20.9±0.5 mV, an effect unchanged by 500 nM ouabain but abolished by 500 μM ouabain. We conclude that under basal conditions, Na+/K+‐ATPases containing α2‐ and/or α3‐subunits are partially responsible for the observed K+‐induced effects. The opening of myocyte K+ channels (by levcromakalim or phenylephrine) creates a ‘K+ cloud’ around the cells which fully activates Na+/K+‐ATPase and thereby abolishes further responses to [K+]o elevation. British Journal of Pharmacology (2002) 136, 918–926. doi:

ACh-induced relaxations of rabbit small mesenteric arteries: role of arachidonic acid metabolites and K+

“…In contrast, K ϩ does not appear to significantly contribute to the EDHF response in arteries such as porcine coronary, guinea pig carotid, and mouse mesenteric artery (6,25). K ϩ release in the myoendothelial space relaxes the adjacent smooth muscle by activating smooth muscle K ir channels and possibly Na ϩ -K ϩ -ATPase (7,22,29). In the present study, ACh-induced EDHF-dependent relaxations were inhibited by charybdotoxin.…”

“…Arterial segments (1.5 mm long) were threaded on two stainless steel wires (40 m diameter) and mounted on a four-chamber wire myograph (model 610M; Danish Myo Technology). Arteries were equilibrated at 37°C for 30 min in physiological saline solution (PSS) containing (in mM): 119 NaCl, 4.7 KCl, 2.5 CaCl 2, 1.17 MgSO4, 24 NaHCO3, 1.18 KH2PO4, 0.026 EDTA, and 5.5 glucose, bubbled with 95% O2-5% CO2 (29). The resting tension was set at 1 mN.…”

Aged Spontaneously Hypertensive Rats Exhibit a Selective Loss of EDHF-Mediated Relaxation in the Renal Artery

“…26 The efflux of K ϩ ions through Ca 2ϩ -dependent K ϩ channels has been suggested to result in a sufficient increase in the subendothelial K ϩ concentration to activate inwardly rectifying K ϩ channels and/or the Na-K-ATPase in smooth muscle cells. 10,[27][28][29] There are, however, other means of transferring hyperpolarization from one cell type to another. For example, hyperpolarizing factor(s) such as EETs could be released from endothelial cells.…”

Contraction by Ca2+ Influx via the L-Type Ca2+ Channel Voltage Window in Mouse Aortic Segments is Modulated by Nitric Oxide

“…Deviation of measured Vm from the K + equilibrium potential (Nernstian VK) was largest at physiological K + concentrations, indicating that in non-stimulated VSMCs other ions than K + contribute in setting the resting Vm ( figure 7A). However, by adding levcromakalim, a drug that sets Vm to VK by activating ATP-dependent K + channels (Knot & Nelson, 1998;Weston et al, 2002), Vm of the VSMCs could be hyperpolarised to VK. Indeed, when measured with intracellular microelectrodes, the resting Vm of VSMCs of aortic segments was -60.1±2.6 mV (n=8), which could be repolarized with levcromakalim to -84 mV.…”