NOS Inhibition Enhances Myogenic Tone by Increasing Rho-Kinase Mediated Ca2 Sensitivity in the Male but Not the Female Gerbil Spiral Modiolar ArteryReport as inadecuate




NOS Inhibition Enhances Myogenic Tone by Increasing Rho-Kinase Mediated Ca2 Sensitivity in the Male but Not the Female Gerbil Spiral Modiolar Artery - Download this document for free, or read online. Document in PDF available to download.

Cochlear blood flow regulation is important to prevent hearing loss caused by ischemia and oxidative stress. Cochlear blood supply is provided by the spiral modiolar artery SMA. The myogenic tone of the SMA is enhanced by the nitric oxide synthase NOS blocker L-NG-Nitro-Arginine LNNA in males, but not in females. Here, we investigated whether this gender difference is based on differences in the cytosolic Ca2+ concentration and-or the Ca2+ sensitivity of the myofilaments. Vascular diameter, myogenic tone, cytosolic Ca2+, and Ca2+ sensitivity were evaluated in pressurized SMA segments isolated from male and female gerbils using laser-scanning microscopy and microfluorometry. The gender difference of the LNNA-induced tone was compared, in the same vessel segments, to tone induced by 150 mM K+ and endothelin-1, neither of which showed an apparent gender-difference. Interestingly, LNNA-induced tone in male SMAs was observed in protocols that included changes in intramural pressure, but not when the intramural pressure was held constant. LNNA in male SMAs did not increase the global Ca2+ concentration in smooth muscle cells but increased the Ca2+ sensitivity. This increase in the Ca2+ sensitivity was abolished in the presence of the guanylyl cyclase inhibitor ODQ or by extrinsic application of either the nitric oxide NO-donor DEA-NONOate or the cGMP analog 8-pCPT-cGMP. The rho-kinase blocker Y27632 decreased the basal Ca2+ sensitivity and abolished the LNNA-induced increase in Ca2+ sensitivity in male SMAs. Neither LNNA nor Y27632 changed the Ca2+ sensitivity in female SMAs. The data suggest that the gender difference in LNNA-induced tone is based on a gender difference in the regulation of rho-kinase mediated Ca2+ sensitivity. Rho-kinase and NO thus emerge as critical factors in the regulation of cochlear blood flow. The larger role of NO-dependent mechanisms in male SMAs predicts greater restrictions on cochlear blood flow under conditions of impaired endothelial cell function.



Author: Katrin Reimann , Gayathri Krishnamoorthy , Philine Wangemann

Source: http://plos.srce.hr/



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