Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA353

Poster Communications

The mechanisms underlying cooling induced contraction in detrusor smooth muscle involves neither TRPA1 nor TRPM8.

S. Kajioka2,1, T. Maki2, Y. Kudo3, M. Etoh2

1. Clinical Pharmacology, Kyushu Univerity, Fukuoka, Fukuoka, Japan. 2. Urology, Kyushu University, Fukuoka, Fukuoka, Japan. 3. Gynecology, HIroshima University, Hiroshima, Hiroshima, Japan.

Treatment of underactive bladder (UAB) is not established. Cooling induced contraction (CIC) of detrusor smooth muscle had been reported (Seham, et al, 1999), however the precise mechanism is not conclusively understood. The present study aimed to elucidate the mechanism of CIC, and examined using TRPA1 and TRPM8 knockout mice. Materials: Isolated intact detrusor preparations were obtained from human and TRPA1/TRPM8 (These channels are activated by low temperature.) knockout mice bladder. The procedures of human tissue have been approved by ethical committee at Kyushu University medical school. The urinary bladder were obtained from the patients who underwent radical cystectomy after approval of informed consent. The study protocol of mice was approved by the Animal Care and Committee of Kyushu University. The mice were sacrified with deep anesthesia (>5% Isofulrane) and urinary bladder were immediately isolated. Tension Force Measurement: The detrusor smooth muscle was dissected into small strips measuring approximately 1 mm in width, and 3-4 mm in length for preparation. These strips of detrusor smooth muscle were mounted to transducer for isometric force recording. Ca2+-imaging study: Human detrusor smooth muscle cells were cultured on coverslips and incubated with fluo-4/AM. Fluo-4 fluorescence images were obtained using a confocal-scannning microscope. Values are means ± S.E.M., compared by student's t-test. Results [Results] The graded extracellular temperature change from 37 °C to 10 °C inversely induced a sustained contraction, while reversed by returning temperature (Fig. 1A). Even in the presence of tetrodotoxin and atropine, these responses were also reproducible. Ca2+-free extracellular solution (0.003 ± 0.002 fold, n = 4) or nifedipine (0.08 ± 0.03 fold, n=3) or Caffeine (0.01 ± 0.004 fold, n = 4) well inhibited CIC. Cycropiasonic acid (0.83 ± 0.08 fold, n = 4) or Xestospongin C (1.09 ± 0.03 fold, n = 4) or Thapsigargin (1.23 ± 0.13 fold, n = 4) did not suppress CIC(Fig. 1B). Rise of intracellular Ca2+ concentration ([Ca2+] i) induced by cooling and failure of [Ca2+]i increase by removing extracellular Ca2+ were confirmed (Fig.1C).TRPA1 and TRPM8, activate by cold, knock out mice were also occurred to CIC as well as wild type mice (wild: 0.94±0.27 g/g n=9, TRPA1KO: 0.75±0.05 g/g n=11, TRPM8KO: 0.91±0.33 g/g n=4)(Fig.1D). Conclusion The present study indicated that CIC appeared to result from myogenic origin whether or not neural control. Extracellular Ca2+ is essential for the generation of CIC, suggesting that mechanism underlying CIC requires the transmembrane Ca2+ entry or intracellular Ca2+ metabolic process. This CIC was not provoked by the activation of representative cooling induced activation ion channel, TRPA1 and TRPM8. If this mechanism is further understood, it might lead to the development new treatment of UAB.

Where applicable, experiments conform with Society ethical requirements