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Ca ion-independent tension development in smooth muscle and its inhibition by the rise of cytosolic free ca ion
2413 I P.fr.352 [
Ca ion-independent tension developmem in smooth muscle and its inhibition by the rise of cytosolic free Ca ion Karibe, H., Suga, O., Fukuzald, A., Gokita, T., Matsuo, K. and Uchida, M.K. Department of MolecularPharmacology, Meiji Collegeof Pharmacy, 1-35-23 Nozawa, Setagaya-ku, Tokyo, 154 Japan In Ca ion-free solution with EGTA, various smooth muscles develop tonic tension in response to various receptor agonists and also to vanadate. The tension development can be repeated many times and its duration is very long. This tension development was named "Ca-free contraction" by the late Dr. KJyoshi Sakai (Sakai and Uchida, 1980) in meaning the contraction in the Ca ion-free medium although the tension development is too small and too sustained to be called "contraction". But we think this tension is comparable to the tonus of organs in vivo and elucidation of this mechanisms is essential for the understanding of the tonus of organs. For the Ca-free contraction caused by oxytocin in uterine muscle the intracellular level of Ca ion is not changed as measured by a fluorescent Ca ion indicator, fura. 2 Chelation of the intracellular Ca ion with quirt-2 did not affect the Ca-free contraction (Matsuo et al., 1989). Thus the name "Ca-free contraction" has naturally become to mean Ca ion-independent,, tension development. Inhibition of this Ca-free contraction by Ca ion itself was named "Ca-reversal" also by the late K. Sakai (Sakai and Uchida, 1980) and was found in uterine and gastric smooth muscles. This Ca ion-induced relaxation was pharmacologically studied in uterine muscle vAth Ca channel blockers and Ca channel openers and it was suggested that the inhibition by Ca ion was induced by the influx of Ca ion (Matsuo and Uchida, 1987). Here we report the following new findings: 1) In uterine muscle, bradykinin, oxytocin, vasopressin, prostaglandins, angiotensin If, acetylcholine, serotonin and vanadate caused Ca-free contraction. Vanadate was found to act in the cell by entering through the anion channels because anion channel blockers inhibited the Ca-free contraction induced by vanadate. Thus Ca-free contraction is caused both by stimulation of the receptors and by bypassing them. In vanadate-mduced Ca-free contraction we also found no change in the intracellular free Ca ion level as monitorred with fura-2. 2) Both oxytocin-induced and vanadate-induced Ca-free contractions were inhibited by protein kinase inhibitors such as H-7, HA1004 and staurosporine and by cytoskeletal inhibitors such ~ cytochalasin D at low concentrations. These results strongly imply the involvements of protein phosphorylation and dynamics due to the cytoskeletal elements or actin filaments in Ca-free contraction. 3) On the other hand, the movement of Ca ion was monitorred with fura-2 during Ca-reversal and we found that the intracellular Ca ion level indeed rose simultaneously with this Ca ion-induced inhibition either in oxytocin or vanadate-induced contraction, suggesting that the inhibition by Ca ion is on the post-receptor mechanisms. Thus we found both contraction without elevation of cytosofic free Ca ion and relaxation with its elevation, both being opposite to the common knowledge. References Sakai, K. and Uchida, M., 1980, Jpn. J. Pharmacol. 30, 394. Matsuo, K. and Uchida, M.K., 1987, Europ. J. Pharmacol. 140, 295. Matsuo. K., Gokita, T., Karibe, H. and Uchida, M.K., 1989, Biochem. Biophys. Res. Commun. in press.
Ca ion-independent tension developmem in smooth muscle and its inhibition by the rise of cytosolic free Ca ion Karibe, H., Suga, O., Fukuzald, A., Gokita, T., Matsuo, K. and Uchida, M.K. Department of MolecularPharmacology, Meiji Collegeof Pharmacy, 1-35-23 Nozawa, Setagaya-ku, Tokyo, 154 Japan In Ca ion-free solution with EGTA, various smooth muscles develop tonic tension in response to various receptor agonists and also to vanadate. The tension development can be repeated many times and its duration is very long. This tension development was named "Ca-free contraction" by the late Dr. KJyoshi Sakai (Sakai and Uchida, 1980) in meaning the contraction in the Ca ion-free medium although the tension development is too small and too sustained to be called "contraction". But we think this tension is comparable to the tonus of organs in vivo and elucidation of this mechanisms is essential for the understanding of the tonus of organs. For the Ca-free contraction caused by oxytocin in uterine muscle the intracellular level of Ca ion is not changed as measured by a fluorescent Ca ion indicator, fura. 2 Chelation of the intracellular Ca ion with quirt-2 did not affect the Ca-free contraction (Matsuo et al., 1989). Thus the name "Ca-free contraction" has naturally become to mean Ca ion-independent,, tension development. Inhibition of this Ca-free contraction by Ca ion itself was named "Ca-reversal" also by the late K. Sakai (Sakai and Uchida, 1980) and was found in uterine and gastric smooth muscles. This Ca ion-induced relaxation was pharmacologically studied in uterine muscle vAth Ca channel blockers and Ca channel openers and it was suggested that the inhibition by Ca ion was induced by the influx of Ca ion (Matsuo and Uchida, 1987). Here we report the following new findings: 1) In uterine muscle, bradykinin, oxytocin, vasopressin, prostaglandins, angiotensin If, acetylcholine, serotonin and vanadate caused Ca-free contraction. Vanadate was found to act in the cell by entering through the anion channels because anion channel blockers inhibited the Ca-free contraction induced by vanadate. Thus Ca-free contraction is caused both by stimulation of the receptors and by bypassing them. In vanadate-mduced Ca-free contraction we also found no change in the intracellular free Ca ion level as monitorred with fura-2. 2) Both oxytocin-induced and vanadate-induced Ca-free contractions were inhibited by protein kinase inhibitors such as H-7, HA1004 and staurosporine and by cytoskeletal inhibitors such ~ cytochalasin D at low concentrations. These results strongly imply the involvements of protein phosphorylation and dynamics due to the cytoskeletal elements or actin filaments in Ca-free contraction. 3) On the other hand, the movement of Ca ion was monitorred with fura-2 during Ca-reversal and we found that the intracellular Ca ion level indeed rose simultaneously with this Ca ion-induced inhibition either in oxytocin or vanadate-induced contraction, suggesting that the inhibition by Ca ion is on the post-receptor mechanisms. Thus we found both contraction without elevation of cytosofic free Ca ion and relaxation with its elevation, both being opposite to the common knowledge. References Sakai, K. and Uchida, M., 1980, Jpn. J. Pharmacol. 30, 394. Matsuo, K. and Uchida, M.K., 1987, Europ. J. Pharmacol. 140, 295. Matsuo. K., Gokita, T., Karibe, H. and Uchida, M.K., 1989, Biochem. Biophys. Res. Commun. in press.