Regional differences in 5-HT receptors in cerebral and testicular arterioles of the rat as revealed by Ca2+ imaging of real-time confocal microscopy: variances by artery size and organ specificity

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  • Masu Kazuki
    Department of Anatomy, School of Medicine, Iwate Medical University Department of Neurosurgery, School of Medicine, Iwate Medical University
  • Saino Tomoyuki
    Department of Anatomy, School of Medicine, Iwate Medical University
  • Kuroda Takashi
    Department of Anatomy, School of Medicine, Iwate Medical University
  • Matsuura Makoto
    Department of Anatomy, School of Medicine, Iwate Medical University
  • Russa Afadhali Denis
    Department of Anatomy, School of Medicine, Iwate Medical University Department of Anatomy and Histology, Muhimbili University of Health and Allied Sciences, School of Medicine
  • Ishikita Naoyuki
    Department of Anatomy, School of Medicine, Iwate Medical University
  • Satoh Yoh-ichi
    Department of Anatomy, School of Medicine, Iwate Medical University

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Abstract

5-hydroxytriptamine (5-HT) is an important transmitter for vessel constriction. The present study was performed to clarify the effect of 5-HT on smooth muscles in large- and small-sized cerebral and testicular arterioles by confocal microscopy, with special reference to intracellular Ca2+ concentration ([Ca2+]i) dynamics. In cerebral vessels, 5-HT induced a [Ca2+]i increase and the contraction of smooth muscle cells in large- and midsized arterioles (external diameters >50 μm) but not in small-sized arterioles. Conspicuous [Ca2+]i changes by 5-HT were especially observed in the portions close to the cerebral arterial circle, and the 5-HT-induced responses were caused by both Ca2+ influx and mobilization. Experiments using agonists and antagonists also revealed that cerebral arteriole smooth muscles possess 5-HT1a, 1b, 2 (G-protein-coupled type), and 3 (ion channel type) receptors; specifically, 5-HT2 plays a major role in these responses. On the other hand, in testicular vessels, there were few regional differences among responses to 5-HT, and both large- and small-sized arterioles responded to 5-HT. The responses were caused by only Ca2+ mobilization mediated 5-HT1a and 2. These results indicate that arterioles in different tissues may respond to 5-HT in different manners. Regional differences and the size-dependent manner of responses to 5-HT in cerebral blood vessels also indicate that the regulatory mechanism of blood circulation is highly differentiated in each region of the central nervous system.

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