K_Ca channel blockers reveal hyperpolarization and relaxation to K⁺ in rat isolated mesenteric artery

Abstract

Raising extracellular K+ concentration ([K+](o)) around mesenteric resistance arteries reverses depolarization and contraction to phenylephrine. As smooth muscle depolarizes and intracellular Ca(2+) and tension increase, this effect of K+ is suppressed, whereas efflux of cellular K+ through Ca(2+)-activated K+ (K(Ca)) channels is increased. We investigated whether K+ efflux through K(Ca) suppresses the action of exogenous K+ and whether it prestimulates smooth muscle Na(+)-K(+)-ATPase. Under isometric conditions, 10.8 mM [K+](o) had no effect on arteries contracted >10 mN, unless 100 nM iberiotoxin (IbTX), 100 nM charybdotoxin (ChTX), and/or 50 nM apamin were present. Simultaneous measurements of membrane potential and tension showed that phenylephrine depolarized and contracted arteries to -32.2 +/- 2.3 mV and 13.8 +/- 1.6 mN (n = 5) after blockade of K(Ca), but 10.8 mM K+ reversed fully the responses (107.6 +/- 8.6 and 98.8 +/- 0.6%, respectively). Under isobaric conditions and preconstriction with phenylephrine, 10.7 mM [K+](o) reversed contraction at both 50 mmHg (77.0 +/- 8.5%, n = 9) and 80 mmHg (83.7 +/- 5.5%, n = 5). However, in four additional vessels at 80 mmHg, raising K+ failed to reverse contraction unless ChTX was present. Increases in isometric and decreases in isobaric tension with phenylephrine were augmented by either ChTX or ouabain (100 microM), whereas neither inhibitor altered tension under resting conditions. Inhibition of cellular K+ efflux facilitates hyperpolarization and relaxation to exogenous K+, possibly by indirectly reducing the background activation of Na(+)-K(+)-ATPase.

Rapid Endothelial Cell–Selective Loading of Connexin 40 Antibody Blocks Endothelium-Derived Hyperpolarizing Factor Dilation in Rat Small Mesenteric Arteries

“…11 Loss of K ϩ as an EDHF appears to be caused by BK Ca -channel activation in the smooth muscle (by PE-mediated depolarization and rises in [Ca 2ϩ ] i with consequent K ϩ efflux eventually maxi- mally activating the Na ϩ /K ϩ -ATPase), as it is reversed in the presence of the BK Ca blocker iberiotoxin. 20,42,43 In the present study, possible input from K ϩ as an EDHF was blocked by high levels of background arterial contraction to 5 mol/L PE, 11 isolating EDHF dilation, which may be suggested to be attributable to MEGJs in this artery. 9 The present study provides direct evidence that the MEGJs mediate the persistent dilation.…”

“…In marked contrast, raising the concentration of PE to evoke maximal contraction (and inhibit the simultaneous influence of diffusible EDHF apparent during submaximal stimulation 11,20 ) was associated with block of EDHF dilation ( Figure 3A and 3B and online Figure IIIA). In vessels contracted with 5 mol/L PE, the R max was only 26.7Ϯ8.8% (nϭ11), whereas subsequent addition of 3 mol/L levcromakalim evoked complete dilation (96.9Ϯ0.9%, nϭ4; Figure 3A).…”

“…Segments (2-to 3-mm long) of a third-order branch (ID, Ϸ250 to 350 m) of superior mesenteric artery were dissected at 4°C and cannulated with glass pipettes (OD, Ϸ150 m) in a myograph (Danish Myotechnology 120CP). 20 To ensure optimal reactivity, the artery was pressurized (50 mm Hg) and stretched longitudinally by 20%. 21 After 30 minutes superfusion at 37°C, reactivity was assessed by contraction with 3 mol/L PE, followed by endothelium-dependent relaxation to 1 mol/L acetylcholine (ACh).…”

Evidence in Favor of a Calcium-Sensing Receptor in Arterial Endothelial Cells

“…To determine whether the extracellular K ϩ cloud associated with phenylephrine-induced contractions 24,25 inhibited the action of calindol, we tested whether, as with other endotheliumdependent hyperpolarizations, 26 any such inhibitory effect could be reversed by iberiotoxin (a selective inhibitor of the largeconductance Ca 2ϩ -sensitive K ϩ -channel, BK Ca 27 ). Phenylephrine (1 mol/L) depolarized the smooth muscle by 12.9Ϯ0.7 mV (nϭ4) and in its presence the responses to 1-EBIO and calindol were markedly reduced in comparison to those before phenylephrine addition (Figure 4a and 4b).…”

(−)Doxazosin is a necessary component for the hypotensive effect of (±)doxazosin during long-term administration in conscious rats

“…The K-H solution was maintained at 37 °C and aerated with 95% O 2 and 5% CO 2 . Endothelium-denuded arteries were used only if acetylcholine (1 μmol/L) was unable to relax the arteries by >10% in the preparations precontracted with 0.3 μmol/L NA [21] .…”