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Interaction between spontaneous and neurally mediated regulation of smooth muscle tone in the rabbit corpus cavernosum
Author(s) -
Hashitani Hikaru,
Yanai Yoshimasa,
Shirasawa Nobuyuki,
Soji Tsuyoshi,
Tomita Akihiro,
Kohri Kenjiro,
Suzuki Hikaru
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.099309
Subject(s) - medicine , cyclopiazonic acid , endocrinology , chemistry , stimulation , contraction (grammar) , tetrodotoxin , calcium , biology
Interaction between spontaneous and neurally mediated regulation of tone in the corpus cavernosum smooth muscle (CCSM) of the rabbit was investigated. Changes in isometric muscle tension, intracellular Ca 2 + concentration ([Ca 2 + ] i ) and membrane potential were recorded. CCSM developed spontaneous contractions, transient increases in [Ca 2 + ] i (Ca 2 + transients) and depolarizations. This spontaneous activity was abolished by blocking L‐type Ca 2 + channels (nicardipine, 1 μ m ), sarcoplasmic reticulum Ca 2 + pump activity (cyclopiazonic acid, 10 μ m ), Ca 2 + ‐activated Cl − channels (niflumic acid, 10 μ m ) or cyclooxygenase‐2 (COX‐2; NS‐398, 1 μ m ). Transmural nerve stimulation initiated either α‐adrenergic contractions or nitrergic relaxations of CCSM depending on the level of muscle tone. NS‐398 suppressed nerve‐evoked contractions by about 70% but caused only a 40% reduction in the corresponding Ca 2 + transient. Blocking nitric oxide synthase with N ω ‐nitro‐ l ‐arginine (LNA, 100 μ m ) reinforced nerve‐evoked Ca 2 + transients by about 150%, whilst increasing the corresponding Ca 2 + transients by only 20%. In CCSM preparations that had been pre‐contracted with either noradrenaline (0.3 μ m ) or prostaglandin F 2α (0.1 μ m ), nerve stimulation inhibited about 70% of the contraction and caused only a 20% decrease in [Ca 2 + ] i . Fluorescent immunohistochemistry with COX‐2 antibodies and the reverse transcriptase‐polymerase chain reaction (RT‐PCR) method showed that the enzyme and its mRNA were highly expressed in the CCSM. These results suggest that spontaneously produced prostaglandins (PGs) not only contribute to the generation of spontaneous contractions but also facilitate nerve‐evoked contractions. Conversely, spontaneously released nitric oxide (NO) suppresses excitation. Thus, interaction between spontaneous and neurally mediated regulation of CCSM tone may be fundamental to maintaining the muscle contractility. In addition, both PGs and NO appear to alter CCSM tone with only small changes in [Ca 2 + ] i .