Relationship between force and Ca2+ in anococcygeal and vas deferens smooth muscle cells of the mouse
(1992) Pflügers Archiv - European journal of physiology — Vol. 421, n° 1, p. 43-51 (1992)
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- We compared the changes of the cytoplasmic Ca2+ concentration ([Ca2+]i), as measured with the fluorescent Ca2+ indicator fura-2, and the force development in intact smooth muscle of the tonic anococcygeus (AC) and the phasic vas deferens (VD) of the mouse, during activation by K+ depolarization and by agonists. Resting [Ca2+]i was observed to be 33% lower in AC (80 nM) than in VD (115 nM), while the Ca2+ threshold for contraction was found to be about 120 nM in AC and 160 nM in VD. For a similar [Ca2+]i increase, the agonist stimulation induced a higher force development than the K+ depolarization in both muscle types. During prolonged depolarization, the force/calcium ratio increased in AC but strongly declined in VD. This decline of the force/calcium ratio in VD during depolarization was partially reversed by lowering [Ca2+]o. Our results indicate that the Ca2+ threshold for force development was about 150% of the resting [Ca2+]i in both cell types. The resting [Ca2+]i was lower in the tonic AC than in the phasic VD. Agonist-induced sensitization to Ca2+ occurred in both muscle types. The tonic and phasic smooth muscles essentially differed in the respective modulation of their Ca2+ sensitivity during contraction. The desensitization to Ca2+ was specific for phasic muscle, in which it occurred as an early, time- and Ca(2+)-dependent process that was partially reversible.
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Boland, B., Himpens, B., Gillis, J.-M., & Casteels, R. (1992). Relationship between force and Ca2+ in anococcygeal and vas deferens smooth muscle cells of the mouse. Pflügers Archiv - European journal of physiology, 421(1), 43-51. https://doi.org/10.1007/BF00374732 (Original work published 1992)