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Krishnamoorthy G, Reimann K, Wangemann P. Ryanodine-induced vasoconstriction of the gerbil spiral modiolar artery depends on the Ca 2+ sensitivity but not on Ca 2+ sparks or BK channels. BMC PHYSIOLOGY 2016; 16:6. [PMID: 27806708 PMCID: PMC5093982 DOI: 10.1186/s12899-016-0026-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 10/13/2016] [Indexed: 01/26/2023]
Abstract
Background In many vascular smooth muscle cells (SMCs), ryanodine receptor-mediated Ca2+ sparks activate large-conductance Ca2+-activated K+ (BK) channels leading to lowered SMC [Ca2+]i and vasodilation. Here we investigated whether Ca2+ sparks regulate SMC global [Ca2+]i and diameter in the spiral modiolar artery (SMA) by activating BK channels. Methods SMAs were isolated from adult female gerbils, loaded with the Ca2+-sensitive flourescent dye fluo-4 and pressurized using a concentric double-pipette system. Ca2+ signals and vascular diameter changes were recorded using a laser-scanning confocal imaging system. Effects of various pharmacological agents on Ca2+ signals and vascular diameter were analyzed. Results Ca2+ sparks and waves were observed in pressurized SMAs. Inhibition of Ca2+ sparks with ryanodine increased global Ca2+ and constricted SMA at 40 cmH2O but inhibition of Ca2+ sparks with tetracaine or inhibition of BK channels with iberiotoxin at 40 cmH2O did not produce a similar effect. The ryanodine-induced vasoconstriction observed at 40 cmH2O was abolished at 60 cmH2O, consistent with a greater Ca2+-sensitivity of constriction at 40 cmH2O than at 60 cmH2O. When the Ca2+-sensitivity of the SMA was increased by prior application of 1 nM endothelin-1, ryanodine induced a robust vasoconstriction at 60 cmH2O. Conclusions The results suggest that Ca2+ sparks, while present, do not regulate vascular diameter in the SMA by activating BK channels and that the regulation of vascular diameter in the SMA is determined by the Ca2+-sensitivity of constriction.
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Affiliation(s)
- Gayathri Krishnamoorthy
- Anatomy & Physiology Department, Cell Physiology Laboratory, Kansas State University, 228 Coles Hall, Manhattan, Kansas, 66506-5802, USA
| | - Katrin Reimann
- Anatomy & Physiology Department, Cell Physiology Laboratory, Kansas State University, 228 Coles Hall, Manhattan, Kansas, 66506-5802, USA.,Department of Otolaryngology-Head and Neck Surgery, Tübingen Hearing Research Centre, and Molecular Physiology of Hearing, University of Tübingen, Tübingen, Germany
| | - Philine Wangemann
- Anatomy & Physiology Department, Cell Physiology Laboratory, Kansas State University, 228 Coles Hall, Manhattan, Kansas, 66506-5802, USA.
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Chemical synthesis of tetracyclic terpenes and evaluation of antagonistic activity on endothelin-A receptors and voltage-gated calcium channels. Bioorg Med Chem 2015; 23:5985-98. [PMID: 26190460 DOI: 10.1016/j.bmc.2015.06.055] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Revised: 06/12/2015] [Accepted: 06/20/2015] [Indexed: 11/23/2022]
Abstract
A class of tetracyclic terpenes was synthesized and evaluated for antagonistic activity of endothelin-1 (ET-1) induced vasoconstriction and inhibitory activity of voltage-activated Ca(2+) channels. Three repeated Robinson annulation reactions were utilized to construct the tetracyclic molecules. A stereoselective reductive Robinson annulation was discovered for the formation of optically pure tricyclic terpenes. Stereoselective addition of cyanide to the hindered α-face of tetracyclic enone (-)-18 was found and subsequent transformation into the aldehyde function was affected by the formation of bicyclic hemiiminal (-)-4. Six selected synthetic tetracyclic terpenes show inhibitory activities in ET-1 induced vasoconstriction in the gerbil spiral modiolar artery with putative affinity constants ranging between 93 and 319 nM. Moreover, one compound, (-)-3, was evaluated further and found to inhibit voltage-activated Ca(2+) currents but not to affect Na(+) or K(+) currents in dorsal root ganglion cells under similar concentrations. These observations imply a dual mechanism of action. In conclusion, tetracyclic terpenes represent a new class of hit molecules for the discovery of new drugs for the treatment of pulmonary hypertension and vascular related diseases.
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Shi X, Zhang F, Urdang Z, Dai M, Neng L, Zhang J, Chen S, Ramamoorthy S, Nuttall AL. Thin and open vessel windows for intra-vital fluorescence imaging of murine cochlear blood flow. Hear Res 2014; 313:38-46. [PMID: 24780131 DOI: 10.1016/j.heares.2014.04.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2013] [Revised: 03/07/2014] [Accepted: 04/15/2014] [Indexed: 12/20/2022]
Abstract
Normal microvessel structure and function in the cochlea is essential for maintaining the ionic and metabolic homeostasis required for hearing function. Abnormal cochlear microcirculation has long been considered an etiologic factor in hearing disorders. A better understanding of cochlear blood flow (CoBF) will enable more effective amelioration of hearing disorders that result from aberrant blood flow. However, establishing the direct relationship between CoBF and other cellular events in the lateral wall and response to physio-pathological stress remains a challenge due to the lack of feasible interrogation methods and difficulty in accessing the inner ear. Here we report on new methods for studying the CoBF in a mouse model using a thin or open vessel-window in combination with fluorescence intra-vital microscopy (IVM). An open vessel-window enables investigation of vascular cell biology and blood flow permeability, including pericyte (PC) contractility, bone marrow cell migration, and endothelial barrier leakage, in wild type and fluorescent protein-labeled transgenic mouse models with high spatial and temporal resolution. Alternatively, the thin vessel-window method minimizes disruption of the homeostatic balance in the lateral wall and enables study CoBF under relatively intact physiological conditions. A thin vessel-window method can also be used for time-based studies of physiological and pathological processes. Although the small size of the mouse cochlea makes surgery difficult, the methods are sufficiently developed for studying the structural and functional changes in CoBF under normal and pathological conditions.
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Affiliation(s)
- Xiaorui Shi
- Oregon Hearing Research Center, Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA.
| | - Fei Zhang
- Oregon Hearing Research Center, Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA
| | - Zachary Urdang
- Oregon Hearing Research Center, Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA
| | - Min Dai
- Oregon Hearing Research Center, Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA
| | - Lingling Neng
- Oregon Hearing Research Center, Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA
| | - Jinhui Zhang
- Oregon Hearing Research Center, Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA
| | - Songlin Chen
- Oregon Hearing Research Center, Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA
| | - Sripriya Ramamoorthy
- Oregon Hearing Research Center, Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA
| | - Alfred L Nuttall
- Oregon Hearing Research Center, Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA
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Reimann K, Krishnamoorthy G, Wangemann P. NOS inhibition enhances myogenic tone by increasing rho-kinase mediated Ca2+ sensitivity in the male but not the female gerbil spiral modiolar artery. PLoS One 2013; 8:e53655. [PMID: 23301097 PMCID: PMC3536759 DOI: 10.1371/journal.pone.0053655] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Accepted: 12/04/2012] [Indexed: 11/22/2022] Open
Abstract
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.
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Affiliation(s)
- Katrin Reimann
- Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas, United States of America
- Universitätsklinik für Hals-, Nasen- und Ohrenheilkunde, Eberhard-Karls Universität, Tübingen, Germany
| | - Gayathri Krishnamoorthy
- Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas, United States of America
| | - Philine Wangemann
- Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas, United States of America
- * E-mail:
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Abstract
Normal blood supply to the cochlea is critically important for establishing the endocochlear potential and sustaining production of endolymph. Abnormal cochlear microcirculation has long been considered an etiologic factor in noise-induced hearing loss, age-related hearing loss (presbycusis), sudden hearing loss or vestibular function, and Meniere's disease. Knowledge of the mechanisms underlying the pathophysiology of cochlear microcirculation is of fundamental clinical importance. A better understanding of cochlear blood flow (CoBF) will enable more effective management of hearing disorders resulting from aberrant blood flow. This review focuses on recent discoveries and findings related to the physiopathology of the cochlear microvasculature.
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Affiliation(s)
- Xiaorui Shi
- Oregon Hearing Research Center (NRC04), Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
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Krishnamoorthy G, Regehr K, Berge S, Scherer EQ, Wangemann P. Calcium sparks in the intact gerbil spiral modiolar artery. BMC PHYSIOLOGY 2011; 11:15. [PMID: 21871098 PMCID: PMC3170618 DOI: 10.1186/1472-6793-11-15] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Accepted: 08/26/2011] [Indexed: 11/18/2022]
Abstract
Background Calcium sparks are ryanodine receptor mediated transient calcium signals that have been shown to hyperpolarize the membrane potential by activating large conductance calcium activated potassium (BK) channels in vascular smooth muscle cells. Along with voltage-dependent calcium channels, they form a signaling unit that has a vasodilatory influence on vascular diameter and regulation of myogenic tone. The existence and role of calcium sparks has hitherto been unexplored in the spiral modiolar artery, the end artery that controls blood flow to the cochlea. The goal of the present study was to determine the presence and properties of calcium sparks in the intact gerbil spiral modiolar artery. Results Calcium sparks were recorded from smooth muscle cells of intact arteries loaded with fluo-4 AM. Calcium sparks occurred with a frequency of 2.6 Hz, a rise time of 17 ms and a time to half-decay of 20 ms. Ryanodine reduced spark frequency within 3 min from 2.6 to 0.6 Hz. Caffeine (1 mM) increased spark frequency from 2.3 to 3.3 Hz and prolonged rise and half-decay times from 17 to 19 ms and from 20 to 23 ms, respectively. Elevation of potassium (3.6 to 37.5 mM), presumably via depolarization, increased spark frequency from 2.4 to 3.2 Hz. Neither ryanodine nor depolarization changed rise or decay times. Conclusions This is the first characterization of calcium sparks in smooth muscle cells of the spiral modiolar artery. The results suggest that calcium sparks may regulate the diameter of the spiral modiolar artery and cochlear blood flow.
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Mann ZF, Duchen MR, Gale JE. Mitochondria modulate the spatio-temporal properties of intra- and intercellular Ca2+ signals in cochlear supporting cells. Cell Calcium 2009; 46:136-46. [PMID: 19631380 DOI: 10.1016/j.ceca.2009.06.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2009] [Revised: 06/12/2009] [Accepted: 06/28/2009] [Indexed: 10/20/2022]
Abstract
In the cochlea, cell damage triggers intercellular Ca2+ waves that propagate through the glial-like supporting cells that surround receptor hair cells. These Ca2+ waves are thought to convey information about sensory hair cell-damage to the surrounding supporting cells within the cochlear epithelium. Mitochondria are key regulators of cytoplasmic Ca2+ concentration ([Ca2+](cyt)), and yet little is known about their role during the propagation of such intercellular Ca2+ signalling. Using neonatal rat cochlear explants and fluorescence imaging techniques, we explore how mitochondria modulate supporting cell [Ca2+](cyt) signals that are triggered by ATP or by hair cell damage. ATP application (0.1-50 microM) caused a dose dependent increase in [Ca2+](cyt) which was accompanied by an increase in mitochondrial calcium. Blocking mitochondrial Ca2+ uptake by dissipating the mitochondrial membrane potential using CCCP and oligomycin or using Ru360, an inhibitor of the mitochondrial Ca2+ uniporter, enhanced the peak amplitude and duration of ATP-induced [Ca2+](cyt) transients. In the presence of Ru360, the mean propagation velocity, amplitude and extent of spread of damage-induced intercellular Ca2+ waves was significantly increased. Thus, mitochondria function as spatial Ca2+ buffers during agonist-evoked [Ca2+](cyt) signalling in cochlear supporting cells and play a significant role in regulating the spatio-temporal properties of intercellular Ca2+ waves.
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Affiliation(s)
- Zoë F Mann
- UCL Ear Institute, 332 Gray's Inn Road, London WC1X 8EE, UK; Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK
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Scherer EQ, Arnold W, Wangemann P. Pharmacological reversal of endothelin-1 mediated constriction of the spiral modiolar artery: a potential new treatment for sudden sensorineural hearing loss. BMC EAR, NOSE, AND THROAT DISORDERS 2005; 5:10. [PMID: 16316469 PMCID: PMC1315339 DOI: 10.1186/1472-6815-5-10] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/16/2005] [Accepted: 11/29/2005] [Indexed: 11/10/2022]
Abstract
Background Vasospasm of the spiral modiolar artery (SMA) may cause ischemic stroke of the inner ear. Endothelin-1 (ET-1) induces a strong, long-lasting constriction of the SMA by increasing contractile apparatus Ca2+ sensitivity via Rho-kinase. We therefore tested several Rho-kinase inhibitors and a cell-permeable analogue of cAMP (dbcAMP) for their ability to reverse ET-1-induced constriction and Ca2+-sensitization. Methods The present study employed SMA isolated from gerbil temporal bones. Ca2+sensitivity was evaluated by correlating vascular diameter and smooth muscle cell [Ca2+]i, measured by fluo-4-microfluorometry and videomicroscopy. Results The Rho-kinase inhibitors Y-27632, fasudil, and hydroxy-fasudil reversed ET-1-induced vasoconstriction with an IC50 of 3, 15, and 111 μmol/L, respectively. DbcAMP stimulated a dose-dependent vasodilation (Ec50 = 1 mmol/L) and a reduction of [Ca2+]i (EC50 = 0.3 μmol/L) of ET-1-preconstricted vessels (1 nmol/L). Fasudil and dbcAMP both reversed the ET-1-induced increase in Ca2+ sensitivity. Conclusion Rho-kinase inhibition and dbcAMP reversed ET-1-induced vasoconstriction and Ca2+-sensitization. Therefore, Rho-kinase inhibitors or cAMP modulators could possess promise as pharmacological tools for the treatment of ET-1-induced constriction, ischemic stroke and sudden hearing loss.
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Affiliation(s)
- Elias Q Scherer
- Cell Physiology Laboratory, Dept. Anatomy & Physiology, Kansas State University, Manhattan, KS 66506, USA
- Department of Otorhinolaryngology, Head and Neck Surgery, Technical University of Munich, Klinikum rechts der Isar, Ismaninger Str. 22, 81675 Munich, Germany
| | - Wolfgang Arnold
- Department of Otorhinolaryngology, Head and Neck Surgery, Technical University of Munich, Klinikum rechts der Isar, Ismaninger Str. 22, 81675 Munich, Germany
| | - Philine Wangemann
- Cell Physiology Laboratory, Dept. Anatomy & Physiology, Kansas State University, Manhattan, KS 66506, USA
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Jiang ZG, Shi X, Zhao H, Si JQ, Nuttall AL. Basal nitric oxide production contributes to membrane potential and vasotone regulation of guinea pig in vitro spiral modiolar artery. Hear Res 2004; 189:92-100. [PMID: 14987756 DOI: 10.1016/s0378-5955(03)00398-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Nitric oxide (NO) is a potent vasodilating agent implicated in cochlear blood flow regulation. We recently demonstrated that exogenously applied NO donor DPTA-NONOate hyperpolarizes both endothelial and smooth muscle cells of in vitro spiral modiolar artery (SMA) via activation of ATP-sensitive K+ channels (K(ATP)). Also, NO was detected in the SMA cells by NO indicator dye in the in vitro basal condition. Using intracellular recording techniques, electrochemical NO-sensing measurement, and a vaso-diameter video tracking method, we investigated the basal release of NO from the in vitro SMA and its role in the vascular function. We found that (1) 300 microM L-NAME, a NO synthase inhibitor, and 3 microM glipizide caused a depolarization of approximately 4.5 and approximately 3.2 mV, respectively, in cells with a resting potential less negative than -60 mV; (2) NO sensor in the close vicinity of the SMA detected a NO concentration of approximately 50 nM that was suppressed by L-NAME and enhanced by L-arginine (1-1000 microM); (3) NO donor DPTA-NONOate (0.1-30 microM) applications produced about 8-245 nM of NO in the recording bath. These data indicate a NO concentration-hyperpolarization relation, with an EC50 of 22 nM. (4) Finally, L-NAME but not glipizide produced a 4.8% reduction in SMA diameter (approximately 50 microm) in the majority of SMAs, whereas NONOate (10 microM) always caused a dilation. Both the induced constriction and dilation were not significantly affected by 3 microM glipizide. We conclude that a significant amount of NO (> 50 nM) is tonically released from the in vitro SMA, which is above the EC50 for activation of K(ATP), and thus contributes to the membrane polarization. The basal release of NO also contributes to vasotone relaxation, but the K(ATP) activation appears to play little role in the relaxation of the in vitro SMA.
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Affiliation(s)
- Zhi-Gen Jiang
- Oregon Hearing Research Center, NRC-04, Oregon Health and Sciences University, Portland, OR 97201, USA.
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Scherer EQ, Herzog M, Wangemann P. Endothelin-1-induced vasospasms of spiral modiolar artery are mediated by rho-kinase-induced Ca(2+) sensitization of contractile apparatus and reversed by calcitonin gene-related Peptide. Stroke 2002; 33:2965-71. [PMID: 12468798 DOI: 10.1161/01.str.0000043673.22993.fd] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND AND PURPOSE Vasospasms of the spiral modiolar artery may cause an ischemic stroke of the inner ear that manifests itself by a sudden hearing loss. Previously we have shown that endothelin-1 (ET-1) induces vasospasms of the spiral modiolar artery. Here we tested the hypotheses that ET-1-induced vasospasms are (1) reversible by ET(A) receptor antagonists; (2) mediated by a Ca(2+) sensitization of the contractile apparatus via a Rho-kinase-induced inhibition of myosin light chain phosphatase; and (3) reversible by the vasodilator calcitonin gene-related peptide (CGRP). METHODS The Ca(2+) sensitivity of the contractile apparatus was evaluated by correlation between the smooth muscle cell Ca(2+) concentration and the vascular diameter, which were measured by microfluorometry with the fluorescent dye fluo-4 and videomicroscopy, respectively. RESULTS ET-1-induced vasospasms were prevented but not reversed by the ET(A) receptor antagonists BQ-123 and BMS-182874. The Ca(2+) sensitivity of the contractile apparatus was increased by ET-1 and by inhibition of myosin light chain phosphatase with calyculin A and was decreased by CGRP. ET-1-induced vasospasms and Ca(2+) sensitization were prevented and reversed by the Rho-kinase antagonist Y-27632 and by CGRP. CONCLUSIONS ET-1 induces vasospasms of the spiral modiolar artery via ET(A) receptor-mediated activation of Rho-kinase, inhibition of myosin light chain phosphatase, and an increase in Ca(2+) sensitivity, which is reversed by CGRP. The observation that vasospasms were reversed by Y-27632 but not by BQ-123 or BMS-182874 suggests that Rho-kinase, rather than the ET(A) receptor, is the most promising pharmacological target for the treatment of ET-1-induced vasospasms, ischemic strokes, and sudden hearing loss.
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Affiliation(s)
- Elias Q Scherer
- Anatomy and Physiology Department, Kansas State University, Manhattan, KS 66506, USA
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Ochi K, Kinoshita H, Kenmochi M, Nishino H, Ohashi T. Effects of nimodipine on salicylate ototoxicity. Ann Otol Rhinol Laryngol 2002; 111:1092-6. [PMID: 12498370 DOI: 10.1177/000348940211101206] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The purpose of this study was to examine the effects of nimodipine on salicylate ototoxicity in guinea pigs. The compound action potential (CAP) was recorded at the round window, and the cochlear blood flow (CBF) was measured simultaneously from the lateral wall of the basal turn of the cochlea by laser Doppler flowmetry. After administration of salicylate (100 mg/kg), the CAP thresholds were significantly elevated, by 5 to 20 dB (p < .05), and the CBF was significantly decreased (p < .05). After administration of nimodipine (2 mg/kg), the CAP thresholds were unchanged, but the CBF had increased significantly (p < .05), while systemic blood pressure had decreased significantly (p < .05). Simultaneous administration of both salicylate (100 mg/kg) and nimodipine (2 mg/kg) resulted in significant elevation of the CAP thresholds (p < .05), while the CBF did not decrease. These results suggest that nimodipine prevents the decrease in CBF induced by salicylate, but that nimodipine does not prevent the deterioration in the CAP.
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Affiliation(s)
- Kentaro Ochi
- Department of Otolaryngology, St Marianna University School of Medicine, Kawasaki City, Japan
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Gruber DD, Dang H, Shimozono M, Scofield MA, Wangemann P. Alpha1A-adrenergic receptors mediate vasoconstriction of the isolated spiral modiolar artery in vitro. Hear Res 1998; 119:113-24. [PMID: 9641324 DOI: 10.1016/s0378-5955(98)00036-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Several lines of evidence suggest that cochlear blood flow is under the control of the sympathetic nervous system and that this control is mediated via alpha-adrenergic receptors. The goal of the present study was to determine whether alpha-adrenergic receptors mediate vasoconstriction of the spiral modiolar artery and, if so, to determine which subtype dominates this response. Vascular diameter was measured with video microscopy in the isolated superfused spiral modiolar artery in vitro. The diameter of the spiral modiolar artery under control conditions was 61 +/- 2 microm (n = 60). Spontaneous vasomotion was observed in most specimens. Addition of norepinephrine to the superfusate caused a phasic vasoconstriction and an increase in the amplitude of vasomotion. These effects were limited to the vicinity of arteriolar branch points of the spiral modiolar artery. Norepinephrine-induced vasoconstriction occurred with EC50 of (1.9 +/- 0.4) x 10(-5) M (n = 44) and the vascular diameter was maximally reduced by a factor of 0.87 +/- 0.01 (n = 29). Neither the phasic nature nor the EC50 of the norepinephrine-induced vasoconstrictions was altered in the presence of the beta2-adrenergic receptor antagonist 10(-5) M ICI118551 or the nitric oxide synthase inhibitor 10(-4) M NOARG. In contrast, the alpha2-adrenergic receptor antagonist 10(-7) M yohimbine and the alpha1-adrenergic receptor antagonist 10(-9) and 10(-8) M prazosin caused a significant shift in the dose-response curve. The affinity constants (K(DB)) for yohimbine and prazosin were (5+/-2) x 10(-8) M (n=4) and (2.0+/-0.7) x 10(-10) M (n=18), respectively. The alpha1A-adrenergic receptor antagonist 10(-8) M 5-methyl urapidil and the alpha1D-adrenergic receptors antagonist 5 x 10(-6) M BMY7378 caused a significant shift in the dose-response curve. The K(DB) values for 5-methyl urapidil and for BMY7378 were (2.7 +/- 0.7) x 10(-10) M (n = 8) and (4.4 +/- 2.7) x 10(-7) M (n = 8), respectively. Further, total RNA was isolated from microdissected spiral modiolar arteries and the presence of transcripts for alpha1-adrenergic receptor subtypes was determined by reverse transcription polymerase chain reaction (RT-PCR). Primers specific for gerbil alpha1-adrenergic receptor subtypes were developed using RNA from rat and gerbil brain. Analysis of RNA extracted from the spiral modiolar artery revealed RT-PCR products of the appropriate size for the alpha1A-adrenergic receptor, however, no evidence for the alpha1B- and alpha1D-adrenergic receptor was found. Further, analysis of RNA extracted from blood, which was a contaminant of the microdissected spiral modiolar arteries, revealed no RT-PCR products. Sequence analysis of the RT-PCR product of the alpha1A-adrenergic receptor from the spiral modiolar artery confirmed its identity. Identity between the 175 nt gerbil sequence fragment and the known rat, mouse and human alpha1A-adrenergic receptor sequences was 90.9, 92.0 and 85.2%, respectively. These observations demonstrate that the spiral modiolar artery contains alpha1A-adrenergic receptors which mediate vasoconstriction at branch points.
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Affiliation(s)
- D D Gruber
- Cell Physiology Laboratory, Boys Town National Research Hospital, Omaha, NE 68131, USA
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