Vasodilation induced by oxygen/glucose deprivation is attenuated in cerebral arteries of SUR2 null mice

Abstract

Physiological functions of arterial smooth muscle cell ATP-sensitive K(+) (K(ATP)) channels, which are composed of inwardly rectifying K(+) channel 6.1 and sulfonylurea receptor (SUR)-2 subunits, during metabolic inhibition are unresolved. In the present study, we used a genetic model to investigate the physiological functions of SUR2-containing K(ATP) channels in mediating vasodilation to hypoxia, oxygen and glucose deprivation (OGD) or metabolic inhibition, and functional recovery following these insults. Data indicate that SUR2B is the only SUR isoform expressed in murine cerebral artery smooth muscle cells. Pressurized SUR2 wild-type (SUR2(wt)) and SUR2 null (SUR2(nl)) mouse cerebral arteries developed similar levels of myogenic tone and dilated similarly to hypoxia (<10 mmHg Po(2)). In contrast, vasodilation induced by pinacidil, a K(ATP) channel opener, was ∼71% smaller in SUR2(nl) arteries. Human cerebral arteries also expressed SUR2B, developed myogenic tone, and dilated in response to hypoxia and pinacidil. OGD, oligomycin B (a mitochondrial ATP synthase blocker), and CCCP (a mitochondrial uncoupler) all induced vasodilations that were ∼39-61% smaller in SUR2(nl) than in SUR2(wt) arteries. The restoration of oxygen and glucose following OGD or removal of oligomycin B and CCCP resulted in partial recovery of tone in both SUR2(wt) and SUR2(nl) cerebral arteries. However, SUR(nl) arteries regained ∼60-82% more tone than did SUR2(wt) arteries. These data indicate that SUR2-containing K(ATP) channels are functional molecular targets for OGD, but not hypoxic, vasodilation in cerebral arteries. In addition, OGD activation of SUR2-containing K(ATP) channels may contribute to postischemic loss of myogenic tone.

Fig. 1.

Murine cerebral artery myocytes express sulfonylurea receptor 2B (SUR2B). A: RT-PCR amplified transcripts for SUR1 (169 bp), SUR2A (320 bp), and SUR2B (144 bp) from murine heart cDNA, whereas only SUR1 and SUR2B were amplified from murine brain. In contrast, isolated, selected cerebral artery myocytes only express transcript for SUR2B. B: Western blots indicate that SUR2B is expressed in mouse brain and cerebral arteries and that SUR2B blocking peptide blocks SUR2B detection.

Fig. 2.

Myogenic tone is similar in cerebral arteries of SUR2 wild-type (SUR2_wt) and SUR2 null (SUR2_nl) mice. A: representative traces illustrating that an elevation in intravascular pressure from 10 to 60 mmHg induces a similar myogenic constriction in SUR2_wt and SUR2_nl cerebral arteries. B: mean myogenic tone in SUR2_wt (n = 37) and SUR2_nl (n = 38) arteries, pressurized to 60 mmHg.

Fig. 3.

SUR2 is required for pinacidil- but not hypoxia-induced dilation in murine cerebral arteries. Representative traces (A) and mean data (n = 14 for each) (B) illustrate that pinacidil (5 μM)-induced dilation of cerebral arteries is attenuated in SUR2_nl arteries. Representative traces (C) and mean data (n = 7 for each) (D) indicate that hypoxia (40 min) induces a similar dilation in SUR2_wt and SUR2_nl cerebral arteries. *P < 0.05 when compared with SUR2_wt.

Fig. 4.

Human cerebral arteries express SUR2B and dilate in response to pinacidil and hypoxia. A: Western blots indicate that SUR2B is expressed in human brain and cerebral arteries and that SUR2B blocking peptide blocks SUR2B detection in human brain. B: representative trace illustrating that pressurized (60 mmHg) human cerebral arteries develop steady-state myogenic tone. Representative traces (C) and mean data (n = 4 arteries for each) (D) show that pinacidil (10 μM) and hypoxia (40 min) induce dilation of human cerebral arteries.

Fig. 5.

Oxygen-glucose deprivation (OGD)-induced vasodilation and loss of myogenic tone following reperfusion are attenuated in SUR2_nl cerebral arteries. A: representative traces exemplifying OGD (40 min)-induced dilation and post-OGD loss of steady-state myogenic tone in SUR2_wt and SUR2_nl cerebral arteries. B: mean data (n = 7 for each) illustrating that OGD-induced vasodilation is smaller in SUR2_nl than SUR2_wt arteries. C: mean data (n = 7 for each) indicating that the sustained dilation post-OGD (i.e., sustained diameter − baseline diameter) is smaller in SUR2_nl than SUR2_wt cerebral arteries. *P < 0.05 compared with SUR2_wt.

Fig. 6.

Vasodilation induced by mitochondrial inhibition and loss of myogenic tone following washout are attenuated in SUR2_nl cerebral arteries. A: mean data illustrating that oligomycin B (1 μM; SUR2_wt, n = 6 for each; and SUR2_nl, n = 8 for each)- and CCCP (1 μM; SUR2_wt, n = 4 for each; and SUR2_nl, n = 5 for each)-induced vasodilation is smaller in SUR2_nl than in SUR2_wt arteries. B: mean data demonstrating that the sustained vasodilation after washout of oligomycin B (SUR2_wt, n = 6 for each; and SUR2_nl, n = 8 for each) or CCCP (SUR2_wt, n = 4 for each; and SUR2_nl, n = 5 for each) is smaller in SUR2_nl than in SUR2_wt mouse cerebral arteries. *P < 0.05 compared with SUR2_wt.