A comparative study of cerebral microcirculation during pulsatile and nonpulsatile selective cerebral perfusion: assessment by synchrotron radiation microangiography.

Currently, nonpulsatile selective cerebral perfusion for cerebroprotection against thoracic aortic aneurysm is used in clinical settings. We performed synchrotron radiation microangiography to determine the effects on selective cerebral perfusion modulation by pulsatile flow. We established cerebral perfusion at normothermia and severe hypothermia in anesthetized rats, during which cerebral angiography was performed. NG-nitro-L-arginine-methyl ester hydrochloride (L-NAME) was administered to determine the effect of pulsatile flow with nitric oxide synthesis. In comparison with nonpulsatile flow, the relative diameters of small internal carotid artery were 132.11 ± 5.49% and 114.96 ± 4.60% during pulsatile flow at normothermia and severe hypothermia (p < 0.05). The angiographic scores, an indicator of vessel count, for nonpulsatile and pulsatile flow at normothermia were 0.198 ± 0.013 vs. 0.258 ± 0.010 (p < 0.001) and those at severe hypothermia were 0.158 ± 0.017 vs. 0.214 ± 0.015 (p < 0.01), respectively. In comparison with nonpulsatile flow, the relative internal carotid artery diameters during pulsatile flow with and without L-NAME were 98.50 ± 1.7% vs. 114.96 ± 4.6%, respectively, during severe hypothermia. These results show that pulsatile flow is effective in increasing blood vessel diameter, number of vessels, and perfusion distribution range in the rat model and that it was more effective at normothermia during nitric oxide production.

Structural determinants for the action of grayanotoxin in D1 S4-S5 and D4 S4-S5 intracellular linkers of sodium channel alpha-subunits.

We located a novel binding site for grayanotoxin on the cytoplasmic linkers of voltage-dependent cardiac (rH1) or skeletal-muscle (mu 1) Na(+) channel isoforms (segments S4-S5 in domains D1 and D4), using the alanine scanning substitution method. GTX-modification of Na(+) channels, transiently expressed in HEK 293 cells, was evaluated under whole-cell voltage clamp, from the ratio of maximum chord conductance for modified and unmodified Na(+) channels. In mu 1, mutations K237A, L243A, S246A, K248A, K249A, L250A, S251A, or T1463A, caused a moderate, but statistically significant decrease in this ratio. On making corresponding mutations in rH1, only L244A dramatically reduced the ratio. Because in mu 1, the serine at position 251 is the only heterologous residue with respect to rH1 (Ala-252), we made a double mutant L243A&S251A to match the sequence of mu 1 and rH1 in S4-S5 linkers of both domains. This double mutation resulted in a significant decrease in the ratio, to the same extent as L244A substitution in rH1 did, indicating that the site at Leu-244 in rH1 or at Leu-243 in mu 1 is a novel one, exhibiting a synergistic effect of grayanotoxin.