| 1. |
- Himpens, B, et al.
(författare)
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Free cytosolic calcium during spontaneous contractions in smooth muscle of the guinea-pig mesotubarium
- 1990
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Ingår i: Pflügers Archiv. - 0031-6768. ; 417:4, s. 404-409
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Tidskriftsartikel (refereegranskat)abstract
- The free intracellular calcium ion concentration ([Ca2+]i) was measured simultaneously with isometric force in strips of guinea-pig mesotubarium using the Fura-2 technique. During the relaxed period (5-15 min) between spontaneous contractions [Ca2+]i continues to decrease after full mechanical relaxation to reach a minimal level of 86 +/- 8 nM (n = 9) just before the start of the next contraction. During the spontaneous contractions (5-15 min) [Ca2+]i reached a maximum of 211 +/- 19 nM and then oscillated between 155 +/- 16 nM and 194 +/- 9 nM. Increased extracellular Ca2+ concentration to 10 mM from the standard concentration of 1.5 mM caused a decreased frequency of spontaneous contractions and an increase in [Ca2+]i both in the relaxed and contracted states. In 10 mM extracellular Ca2+, addition of AlF4-, as 1 mM NaF + 10 microM AlCl3, caused a sustained increase in [Ca2+]i and maintained force. Addition of verapamil (10 microM) in this situation decreased [Ca2+]i to the resting level. The results suggest that the cyclic appearance of trains of action potentials is related to variation in [Ca2+]i, possibly via inactivation of Ca2(+)-dependent K+ channels.
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| 2. |
- Lydrup, M L, et al.
(författare)
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Paradoxical decrease in cytosolic calcium with increasing depolarization by potassium in guinea-pig mesotubarium smooth muscle
- 1992
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Ingår i: Pflügers Archiv. - 0031-6768. ; 420:5-6, s. 428-433
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Tidskriftsartikel (refereegranskat)abstract
- The free intracellular Ca2+ concentration ([Ca2+]i) was measured simultaneously with isometric force in strips of guinea-pig mesotubarium using the Fura-2 technique. [Ca2+]i and force were maximal at a relatively low (30 mM) concentration of extracellular K+ ([K+]o), and declined at 90 and 140 mM K+. Plateau values of both [Ca2+]i and force were higher in the presence of 5.10(-6) M ryanodine, indicating that the sarcoplasmic reticulum (SR) contributes to the decline with depolarization. Force and [Ca2+]i at 90 mM K+ were both lower then the high-K+ solution was applied after a period in 30 mM K+ than after a period in normal solution (5.9 mM K+), consistent with inactivation of Ca2+ channels during prolonged depolarization. Addition of carbachol to the depolarized muscle caused a maintained increase in force without maintained increase in [Ca2+]i. We conclude that the decrease in force at increased [K+]o (the "calcium-potassium paradox") is due to a membrane-potential-mediated decrease in [Ca2+]i and, to a lesser extent, to desensitization of the contractile-regulatory apparatus to Ca2+.
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