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Related Experiment Videos

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

M L Lydrup1, B Himpens, G Droogmans

  • 1Department of Physiology and Biophysics, University of Lund, Sweden.

Pflugers Archiv : European Journal of Physiology
|April 1, 1992
PubMed
Summary

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The calcium-potassium paradox in guinea-pig mesotubarium involves a decrease in intracellular calcium concentration ([Ca2+]i) and force with elevated extracellular potassium ([K+]o). This phenomenon is linked to membrane potential changes and calcium channel inactivation.

Area of Science:

  • Physiology
  • Pharmacology
  • Cell Biology

Background:

  • The relationship between extracellular potassium concentration ([K+]o) and smooth muscle contraction is complex.
  • Understanding the role of intracellular calcium ([Ca2+]i) and sarcoplasmic reticulum (SR) in this process is crucial.

Purpose of the Study:

  • To investigate the mechanisms underlying the 'calcium-potassium paradox' in guinea-pig mesotubarium.
  • To determine the contribution of sarcoplasmic reticulum and calcium channel inactivation to force decline at high [K+]o.

Main Methods:

  • Simultaneous measurement of isometric force and intracellular calcium concentration ([Ca2+]i) using the Fura-2 technique.
  • Exposure of isolated guinea-pig mesotubarium strips to varying extracellular potassium concentrations (30, 90, and 140 mM).

Related Experiment Videos

  • Assessment of ryanodine's effect on force and [Ca2+]i, and the impact of prior depolarization on subsequent responses.

    • Main Results:

    • Intracellular calcium ([Ca2+]i) and force peaked at 30 mM [K+]o and declined at higher concentrations (90 and 140 mM).
    • Ryanodine enhanced plateau [Ca2+]i and force, suggesting SR calcium release contributes to the decline.
    • Prolonged depolarization led to lower force and [Ca2+]i, consistent with Ca2+ channel inactivation.
    • Carbachol induced sustained force without sustained [Ca2+]i increase in depolarized muscle.

    Conclusions:

    • The 'calcium-potassium paradox' is primarily caused by a membrane-potential-dependent reduction in intracellular calcium ([Ca2+]i).
    • Desensitization of the contractile apparatus to calcium also contributes to the force decrease.
    • Sarcoplasmic reticulum calcium handling and calcium channel inactivation play significant roles in modulating force during depolarization.