Involvement of ATP-sensitive potassium channels in a model of a delayed vascular hyporeactivity induced by lipopolysaccharide in rats

Abstract

We have investigated the role of ATP-sensitive potassium (K(ATP)) channels in an experimental model of a delayed phase of vascular hyporeactivity induced by lipopolysaccharide (LPS) in rats. After 24 h, from LPS treatment, in anaesthetized rats the bolus injection of phenylephrine (PE) produced an increase in mean arterial pressure (MAP) significantly (P<0.05) reduced in LPS-treated rats compared to the vehicle-treated rats. This reduction was prevented by pre-treatment of rats with glibenclamide (GLB), a selective inhibitor of K(ATP) channels. GLB administration did not affect the MAP in vehicle-treated rats but produced an increase of MAP in rats treated with LPS. Cromakalim (CRK), a selective K(ATP) channel opener, produced a reduction of MAP that was significantly (P<0.05) higher in LPS- than in vehicle-treated rats. In contrast, the hypotension induced by glyceryl trinitrate (GTN) in LPS-treated rats was not distinguishable from that produced in vehicle-treated rats. Experiments in vitro were conducted on aorta rings collected from rats treated with vehicle or LPS 24 h before sacrifice. The concentration-dependent curve to PE was statistically (P<0.005) reduced in aorta rings collected from LPS- compared to vehicle-treated rats. This difference was totally abolished by tetraethylammonium (TEA), a non-selective inhibitor of K+ channels. CRK produced a relaxation of PE precontracted aorta rings higher in rings from LPS- than in vehicle-treated rats. GLB inhibited CRK-induced relaxation in both tissues, abolishing the observed differences. In conclusion, our results indicate an involvement of K(ATP) channels to the hyporesponsiveness of vascular tissue after 24 h from a single injection of LPS in rats. We can presume an increase in the activity of K(ATP) channels on vascular smooth muscle cells but we cannot exclude an increase of K(ATP) channel number probably due to the gene expression activation.

Figure 1

Changes in MAP induced by phenylephrine (10, 30 and 100 μg kg⁻¹ i.v.; PE) in rats treated 24 h before with vehicle or lipopolysaccharide (8×10⁶ u kg⁻¹ i.p.; LPS) and effect of glibenclamide (40 mg kg⁻¹ i.p.; GLB) administered 1 h before the contracting agent. Results are expressed as per cent of basal MAP and shown as mean±s.e.mean of 9–12 animals; ^*P<0.05 vs vehicle ΦP<0.05 vs LPS+GLB and ΦΦP<0.01 vs LPS+GLB.

Figure 2

Effect of glibenclamide (40 mg kg⁻¹ i.p.; GLB) on MAP in rats treated with either vehicle of lipopolysaccharide (8×10⁶ u kg⁻¹ i.p.; LPS) 24 h before the experiment. Results are expressed as per cent of basal MAP and shown as mean±s.e.mean of 6–7 animals; ^*P<0.05.

Figure 3

Reduction of MAP induced by cromakalim (150 μg kg⁻¹ i.v.; CRK) or glyceryl trinitrate (500 μg kg⁻¹ i.v.; GTN) in rats treated with vehicle or lipopolysaccharide (8×10⁶ u kg⁻¹ i.p.; LPS) 24 h before the experiment. Effect of glibenclamide (40 mg kg⁻¹ i.p.; GLB) or L-NAME (3 μg kg⁻¹ min⁻¹) on CRK-induced reduction of MAP. Results are expressed as per cent of basal MAP and shown as mean±s.e.mean of 5–7 animals. ^*P<0.05 vs vehicle alone, ^**P<0.01 vs vehicle alone, ^***P<0.001 vs vehicle alone, ΦP<0.05 vs LPS alone and ΦΦP<0.001 vs LPS alone.

Figure 4

Effect of glibenclamide (30 and 100 μM; GLB; (a), tetraethylammonium (10 mM; TEA; (b) or N^G-nitro-L-arginine methyl ester (100 μM; L-NAME; (c) on concentration-response curve to phenylephrine (1 nM–3 μM; PE) of aorta rings collected from lipopolysaccharide (8×10⁶ u kg⁻¹ i.p.; LPS) or vehicle treated rats 24 h before experiment. Results are expressed as mean±s.e.mean of 12 aorta rings. Curves were compared by analysis of variance (ANOVA) and following results were obtained: (a) vehicle vs LPS P<0.001, vehicle vs vehicle+GLB 30 μM P<0.05, vehicle vs vehicle+GLB 100 μM P<0.001, LPS vs LPS+GLB 30 μM P<0.05, LPS vs LPS+GLB 100 μM P<0.001; (b) vehicle vs LPS P<0.001, vehicle vs vehicle+TEA P>0.05, LPS vs LPS+TEA P<0.001, vehicle vs LPS+TEA P>0.05; (c) vehicle vs LPS P<0.001, vehicle vs vehicle+L-NAME P=0.05, LPS vs LPS+L-NAME P<0.001, vehicle+L-NAME vs LPS+L-NAME P<0.01.

Figure 5

Effect of glibenclamide (30 μM; GLB, (a) or N^G-nitro-L-arginine methyl ester (100 μM; L-NAME; (b) on cromakalim (10 nM–100 μM; CRK) induced vasorelaxation of phenylephrine (1 μM) precontracted aorta rings, collected from vehicle or lipopolysaccharide (8×10⁶ u kg⁻¹ i.p.; LPS) treated rats 24 h before experiment. Results are expressed as mean±s.e.mean of 12 aorta rings. Curves were compared by analysis of variance (ANOVA) and following results were obtained: (a) vehicle vs LPS P<0.001, vehicle vs vehicle+GLB P<0.001, LPS vs LPS+GLB P<0.001, vehicle+GLB vs LPS+GLB P>0.05; (b) vehicle vs LPS P<0.001, vehicle vs vehicle+L-NAME P=0.001, LPS vs LPS+L-NAME P<0.001, vehicle+L-NAME vs LPS+L-NAME P<0.001.