The free cytoplasmic Ca2+ concentration [( Ca2+]i) was measured in the tonic rabbit pulmonary artery and the phasic ileum smooth muscle. 2. Force development and [Ca2+]i were determined during either cumulative or non-cumulative additions of [Ca2+]o to smooth muscles depolarized with 140 mM-K+ solutions. 3. The level to which [Ca2+]i declined in Ca2+-free, 140 mM-K+ solutions was significantly lower in the ileum (40 +/- 4 nM) than in pulmonary artery (77 +/- 5 nM) smooth muscle. 4. The level of [Ca2+]i reached during non-cumulative superfusion with 10 microM and 1 mM [Ca2+]o was higher in the pulmonary artery than in the ileum. 5. The force level reached for a given [Ca2+]i was also higher in the pulmonary artery than in the ileum. 6. During maintained depolarization there was a marked decrease in the sensitivity of ileum smooth muscle tension to [Ca2+]i. 7. We conclude that significant differences exist in the Ca2+ sensitivity of the regulatory/contractile apparatus among different smooth muscles; the lower sensitivity of depolarized ileum than pulmonary artery to [Ca2+]o is due to both differences in Ca2+ metabolism and in the Ca2+ sensitivity of the regulatory contractile system. We suggest that these two mechanisms also contribute to the decline in force during a phasic K+ contracture, and that desensitization to [Ca2+]i contributes to the decline of the K+ contracture in the ileum.
摘要
在强直性兔肺动脉和节律性回肠平滑肌中测量了游离细胞质钙离子浓度([Ca2+]i)。2. 在向用140 mM - K+溶液去极化的平滑肌中累积或非累积添加[Ca2+]o的过程中，测定了张力发展和[Ca2+]i。3. 在无钙的140 mM - K+溶液中，回肠平滑肌([Ca2+]i降至40±4 nM)中[Ca2+]i下降的水平显著低于肺动脉平滑肌(77±5 nM)。4. 在非累积灌注10 microM和1 mM [Ca2+]o期间，肺动脉中达到的[Ca2+]i水平高于回肠。5. 对于给定的[Ca2+]i，肺动脉达到的张力水平也高于回肠。6. 在持续去极化期间，回肠平滑肌张力对[Ca2+]i的敏感性显著降低。7. 我们得出结论，不同平滑肌的调节/收缩装置对Ca2+的敏感性存在显著差异；去极化的回肠对[Ca2+]o的敏感性低于肺动脉，这是由于Ca2+代谢差异和调节收缩系统对Ca2+的敏感性差异所致。我们认为这两种机制也导致了节律性K+挛缩期间的张力下降，并且对[Ca2+]i的脱敏导致了回肠中K+挛缩的下降。
