Invited Symposium: Stroke/Cerebral Vasospasm
G. Pyne (Vascular Smooth Muscle Research Group, MRC Collaborative Centre, UK)
T.A.D. Cadoux-Hudson (Vascular Smooth Muscle Research Group, MRC Collaborative Centre, UK)
Magnesium (Mg++) plays an important role in the energy metabolism of vascular smooth muscle (VSM). It has been shown to stabilize the slowly cycling cross bridge state which VSM employs to maintain long periods of tension at low energy cost. CSF from patients with vasospasm after SAH has previously been shown to stimulate oxygen consumption & tension generation in the porcine carotid artery, but the relationship between Mg++ & vasospasm is yet to be established. The aim of these investigations is to establish a correlation between tension generation & energy metabolism under Mg++ depleted & Mg++ loaded conditions. Lengths of pig carotid artery were mounted between two clamps as strips or two hooks as rings for isometric force measurements. The pig carotid arteries were incubated in phyusiological saline saolution containing 0mM Mg++, 1.2mM Mg++ or 12mM Mg++ for two hours. It was found that the CSFv caused the muscle to generate 72+/-8% of Fmax. Although the Mg++ loaded tissue's response to CSFv with respect to percentage increase from baseline did not differ from control, the basal 02 consumption was lowered from 0.37 +/-0.007 to 0.26+/- 0.014mMols 02 min-1 g dwt-1. Maximal contraction was lowered under Mg++ loaded conditions to 54% of control. Mg++ depletion alone does not appear to have either deleterious or beneficial effects. These results suggest that Mg++ may have some protective effect against the stimulation by CSFv. This could be effected by the aforementioned stabilization of cross bridges, or other mechanisms.
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