Supplementary Material for: Nitric Oxide Suppresses Cerebral Vasomotion by sGC-Independent Effects on Ryanodine Receptors and Voltage-Gated Calcium Channels
2009-09-04T00:00:00Z (GMT) by
<i>Background/Aims:</i> In cerebral arteries, nitric oxide (NO) release plays a key role in suppressing vasomotion. Our aim was to establish the pathways affected by NO in rat middle cerebral arteries. <i>Methods:</i> In isolated segments of artery, isometric tension and simultaneous measurements of either smooth muscle membrane potential or intracellular [Ca<sup>2+</sup>] ([Ca<sup>2+</sup>]<sub>SMC</sub>) changes were recorded. <i>Results:</i> In the absence of <i>L</i>-NAME, asynchronous propagating Ca<sup>2+</sup> waves were recorded that were sensitive to block with ryanodine, but not nifedipine. <i>L</i>-NAME stimulated pronounced vasomotion and synchronous Ca<sup>2+</sup> oscillations with close temporal coupling between membrane potential, tone and [Ca<sup>2+</sup>]<sub>SMC</sub>. If nifedipine was applied together with <i>L</i>-NAME, [Ca<sup>2+</sup>]<sub>SMC</sub> decreased and synchronous Ca<sup>2+</sup> oscillations were lost, but asynchronous propagating Ca<sup>2+</sup> waves persisted. Vasomotion was similarly evoked by either iberiotoxin, or by ryanodine, and to a lesser extent by ODQ. Exogenous application of NONOate stimulated endothelium-independent hyperpolarization and relaxation of either <i>L</i>-NAME-induced or spontaneous arterial tone. NO-evoked hyperpolarization involved activation of BK<sub>Ca</sub> channels via ryanodine receptors (RYRs), with little involvement of sGC. Further, in whole cell mode, NO inhibited current through L-type voltage-gated Ca<sup>2+</sup> channels (VGCC), which was independent of both voltage and sGC. <i>Conclusion:</i> NO exerts sGC-independent actions at RYRs and at VGCC, both of which normally suppress cerebral artery myogenic tone.