Pflügers Archiv

, Volume 432, Issue 5, pp 803–811

Stimulus-dependent modulation of smooth muscle intracellular calcium and force by altered intracellular pH

  • Michael J. Taggart
  • Theodor Burdyga
  • Richard Heaton
  • Susan Wray
Original Article Molecular and Cellular Physiology

Abstract

Measurements of simultaneous force and intracellular Ca2+ concentration ([Ca2+]i) in rat uterine smooth muscle have been made to elucidate the mechanisms involved when force produced spontaneously, by high-K+ depolarization or carbachol is altered by a change of intracellular pH (pHi). Rises in force and [Ca2+]i were closely correlated for all forms of contraction, with the Ca2+ transient peaking before force. In spontaneously active preparations, alkalinization significantly increased, and acidification decreased, force and [Ca2+]i. Inhibition of the sarcoplasmic reticulum ATPase (cyclopiazonic acid) did not affect these changes, whereas removal of external Ca2+ abolished both responses, suggesting that the effect of pHi is on Ca2+ entry. Alkalinization caused a prolongation of the action potential complex, associated with a potentiation of contractile activity. Acidification produced hyperpolarization and abolition of action potentials and spontaneous activity, but did not prevent brief applications of carbachol or high-K+ from producing depolarization and increasing force, suggesting no impairment of the mechanism of generation of the action potential. For depolarized preparations, acidification increased tonic force and [Ca2+]i; the increase in the calcium signal persisted in zero-external calcium. In the presence of carbachol, acidification transiently increased force and [Ca2+]i, followed by a reduction in both. It is concluded that changes in pHi act at more than one step in excitation-contraction coupling and that changes in [Ca2+]i can account for most of the changes in uterine force.

Key words

Calcium Uterus Force pH Carbachol Depolarization 

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Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • Michael J. Taggart
    • 1
  • Theodor Burdyga
    • 2
  • Richard Heaton
    • 1
  • Susan Wray
    • 1
  1. 1.The Physiological LaboratoryThe University of LiverpoolLiverpoolUK
  2. 2.AV Palladine Institute of BiochemistryKiev-30Ukraine

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