Sarcoplasmic Reticulum Function and Contractile Consequences in Ureteric Smooth Muscles

  1. Derek J. Chadwick Organizer and
  2. Jamie A. Goode
  1. Theodor Burdyga and
  2. Susan Wray

Published Online: 7 OCT 2008

DOI: 10.1002/0470853050.ch15

Role Of The Sarcoplasmic Reticulum In Smooth Muscle: Novartis Foundation Symposium 246

Role Of The Sarcoplasmic Reticulum In Smooth Muscle: Novartis Foundation Symposium 246

How to Cite

Burdyga, T. and Wray, S. (2002) Sarcoplasmic Reticulum Function and Contractile Consequences in Ureteric Smooth Muscles, in Role Of The Sarcoplasmic Reticulum In Smooth Muscle: Novartis Foundation Symposium 246 (eds D. J. Chadwick and J. A. Goode), John Wiley & Sons, Ltd, Chichester, UK. doi: 10.1002/0470853050.ch15

Author Information

  1. Department of Physiology, The University of Liverpool, Crown Street, Liverpool L69 3BX, UK

Publication History

  1. Published Online: 7 OCT 2008
  2. Published Print: 15 JUN 2002

Book Series:

  1. Novartis Foundation Symposia

Book Series Editors:

  1. Novartis Foundation

ISBN Information

Print ISBN: 9780470844793

Online ISBN: 9780470853054

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Summary

This paper discusses the role of Ca2+-induced Ca2+ release (CICR) and inositol-1,4,5-trisphosphate (InsP3)-induced Ca2+ release (IICR) from the sarcoplasmic reticulum (SR) in the control of contractile activity in the ureter. The Ca2+ store in guinea-pig ureter has been found to be exclusively a CICR type with ryanodine receptors (RyRs) present. In the rat ureter the SR store is exclusively an IICR type with InsP3 receptors (InsP3Rs) present. Guinea-pig ureteric cells in vitro and in situ have been found to generate Ca2+ sparks—small localized, transient releases from RyRs. The sparks are enhanced by caffeine and blocked by emptying the SR. In rat cells Ca2+ puffs occur in response to agonists, representing the opening of InsP3Rs. The puffs can be abolished by heparin or store emptying. These SR Ca2+-release events affect the excitability of the ureteric cells. In guinea-pig cells, spontaneous transient outward currents (STOCs) can be recorded in response to caffeine application (an agonist for RyR), followed by a shortening of the plateau phase of the action potential. This in turn causes a decrease in the amplitude and duration of the contractions of the ureter. If the SR is inhibited then STOCs are abolished, the action potential plateau prolonged and force increased. Thus it is concluded that the SR acts to limit contraction in the guinea-pig ureter. The mechanism underlying this involves its Ca2+ release being directed to Ca2+-activated K+ channels on the surface membrane and causing STOCs and hyperpolarization, and controlling the duration of the action potential. In rat ureter IICR acts to potentiate force via membrane depolarization and increased L-type Ca2+ entry into the cells. Thus the SR can alter cell signalling and excitation-contraction coupling in the ureter, but its precise role is species dependent. The ureter, with its species-dependent expression of either IICR or CICR provides an ideal system (a natural transgenic model) for studying the SR. Eventually, we will be able to apply this knowledge to the human ureter, to increase our understanding of its functioning in health and disease.