Free radicals mediate actions of oxyhemoglobin on cerebrovascular smooth muscle cells.

Abstract

Single smooth muscle cells were isolated from the basilar artery of the rat by enzymatic dispersion. The membrane properties of the cells were assessed using the patch-electrode voltage-clamp technique, and cell viability was monitored using fluorescein diacetate uptake. Exposure of the cells to oxyhemoglobin (5 microM) resulted in 1) contraction, 2) the appearance of membrane blebs, 3) an increase in the outward potassium currents, 4) a decrease in the membrane resistance, and 5) cell death. In contrast, no effect of oxyhemoglobin on cultured murine neuroblastoma cells was observed. Methemoglobin (100 microM) had no effects on the smooth muscle cells. Catalase (300 units/ml) or dimethyl sulfoxide (0.5%) protected against the effects of oxyhemoglobin; superoxide dismutase (100-1,000 units/ml) provided only partial protection. Exposure of the cells to superoxide anions generated by xanthine (1 mM) plus xanthine oxidase (10 units/l) or to hydrogen peroxide (500 microM) caused an increase in the outward potassium currents without affecting membrane resistance. Generation of hydroxyl radicals by metal ions plus hydrogen peroxide caused the same effects as oxyhemoglobin, that is, an increase in the potassium currents, followed by a decrease in the membrane resistance and cell death. In conclusion, it appears that oxyhemoglobin exerts its effects on vascular smooth muscle cells by the generation of free radicals, chiefly hydroxyl radicals.

Enhanced vasocontraction of rat tail arteries by toxoflavin

“…Or else at low concentrations TXF may open calcium channels to contract SMC whereas at high concentrations (> 10 ,ug ml-1) TXF may mainly generate OFR which induced irreversible vasorelaxation. This is in agreement with other observations that as the production was enhanced, OFR may sequentially cause the contraction and death of smooth muscle cells (Steele et al, 1991).…”

“…In the former case, OFR may inactivate endothelium-generated nitric oxide (NO) (Ikeda et al, 1994) or impair the production of NO (Seccombe et al, 1994). In the latter case, it has been shown that hydroxyl radicals generated by metal ions plus hydrogen peroxide contracted single SMC isolated from the basilar artery of the rat (Steele et al, 1991). Assuming that the biological effects of TXF were due to the generation of OFR, TXF should be able to induce vasocontraction and to increase blood pressure.…”

Potential Contribution of Nuclear Factor-κB to Cerebral Vasospasm after Experimental Subarachnoid Hemorrhage in Rabbits

“…The confluent VSMCs were routinely subcultured at a split ratio of 1:3. Cells from passages 2 to 4 were used, which were characterized as smooth muscle cells by the presence of positive immunohistochemical staining for a-actin and by a characteristic hills-and-valleys appearance (Steele et al, 1991).…”

The Pharmacology of Nitric Oxide in the Peripheral Nervous System of Blood Vessels

“…In isolated, perfused rabbit basilar and dog femoral arteries, it was noted that extraluminal application of oxyHb interfered with the relaxation mediated by NO liberated from the endothelium, although the extent was less than that induced by intraluminal application (Hongo et al, 1988;Toda et al, 1988;Tsuji et al, 1989). The difference in vasoconstrictions in response to oxyHb and L-NA in vivo would be due to non-NO compounds such as vasoconstrictor prostanoids (Toda et al, 1980(Toda et al, , 1991aOkamoto et al, 1984;Fujiwara et al, 1984), free radicals, such as superoxide anions (Katusic and Vanhoutte, 1989) and hydroxyl radicals (Steele et al, 1991), endothelin-1 (Cooks et al, 1991Matsumura et al, 1991;Itoh et al, 1994), etc. Production of endothelin is inhibited by endogenous NO (Ahlborg and Lundberg, 1997;Thorin et al, 1998).…”