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Pflügers Archiv

, Volume 406, Issue 3, pp 259–265 | Cite as

Ca2+-channel current and its modification by the dihydropyridine agonist BAY k 8644 in isolated smooth muscle cells

  • G. Droogmans
  • G. Callewaert
Excitable Tissues and Central Nervous Physiology

Abstract

The electrophysiological properties of single smooth muscle cells isolated from the longitudinal layer of the guinea-pig ileum were studied with the whole-cell patch-clamp technique.
  1. 1.

    The finding of resting potentials between −45 and −50 mV and the occurrence of spontaneous electrical activity when K+ was the predominant intracellular cation indicated that the cells were not leaky or hyperpermeable.

     
  2. 2.

    The existence of an inward Ca2+ current overlapping in time with an outward rectifying K+ current was demonstrated. The latter could be selectively blocked by replacing internal K+ with Cs+ and external Ca2+ with Ba2+.

     
  3. 3.

    Depolarizations to potentials between −40 and +50 mV evoked time-dependent inward currents, with a maximum peak value between −20 and 0 mV. For depolarizations beyond +50 mV time-dependent outward currents appeared. These currents were inhibited by 0.1 mM CdCl2.

     
  4. 4.

    The activation of the inward current showed a sigmoidal time course, and the rate of onset of the current increased at more positive potentials. Inactivation could be described by two exponentials.

     
  5. 5.

    The threshold for activation was about −40 mV, and full activation was reached at 0 mV. Inactivation was complete near 0 mV, whereas the channels were fully available at −80 mV.

     
  6. 6.

    The fully-activated Ca2+-channel current was strongly voltage dependent. The conductance decreased for potentials close to the reversal potential, and showed rectification for hyperpolarizing potentials.

     
  7. 7.

    The Ca2+ agonist BAY k 8644 enhanced the Ca2+-channel current without a significant effect on its kinetics. The fully-activated current and the steady-state activation were enhanced in a rather voltage-independent way.

     

Key words

Smooth muscle Whole-cell patch clamp Ca2+ channels Ca2+ agonists 

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Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • G. Droogmans
    • 1
  • G. Callewaert
    • 1
  1. 1.Laboratorium voor FysiologieLeuvenBelgium

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