Paradoxical decrease in cytosolic calcium with increasing depolarization by potassium in guinea-pig mesotubarium smooth muscle

M L Lydrup, B Himpens, G Droogmans, Per Hellstrand, A P Somlyo

Research output: Contribution to journalArticlepeer-review

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+.
Original languageEnglish
Pages (from-to)428-433
JournalPflügers Archiv
Volume420
Issue number5-6
DOIs
Publication statusPublished - 1992

Subject classification (UKÄ)

  • Physiology

Keywords

  • Calcium
  • Mesotubarium
  • Smooth muscle
  • Fura-2
  • K+ depolarization

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