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Pflügers Archiv

, Volume 418, Issue 4, pp 417–422 | Cite as

Widespread synchronous [Ca2+]i oscillations due to bursting electrical activity in single pancreatic islets

  • Rosa M. Santos
  • Luis M. Rosario
  • Angel Nadal
  • Javier Garcia-Sancho
  • Bernat Soria
  • Miguel Valdeolmillos
Transport Processes, Metabolism and Endocrinology; Kidney, Gastrointestinal Tract, and Exocrine Glands

Abstract

Pancreatic β cells, tightly organized in the islet of Langerhans, secrete insulin in response to glucose in a calcium-dependent manner. The calcium input required for this secretory activity is thought to be provided by an oscillatory electrical activity occurring in the form of “bursts” of calcium action potentials. The previous observation that islet intracellular free Ca2+ levels undergo spontaneous oscillations in the presence of glucose, together with the fact that islet cells are coupled through gap junctions, hinted at a highly effective co-ordination between individual islet cells. Through the use of simultaneous recordings of intracellular calcium and membrane potential it is now reported that the islet calcium waves are synchronized with the β cell bursting electrical activity. This observation suggests that each calcium wave is due to Ca2+ entering the cells during a depolarized phase of electrical activity. Moreover, fura-2 fluorescence image analysis indicates that calcium oscillations occur synchronously across the whole islet tissue. The maximal phase shift between oscillations occurring in different islet cells is estimated as 2 s. This highly co-ordinated oscillatory calcium signalling system may underlie pulsatile insulin secretion and the islet behaviour as a secretory “syncytium”. Since increasing glucose concentration lengthens calcium wave and burst duration without significantly affecting wave amplitude, we further propose that it is the fractional time at an enhanced Ca2+ level, rather than its amplitude, that encodes for the primary response of insulin-secreting cells to fuel secretagogues.

Key words

Intracellular Ca2+ Calcium oscillations Membrane potential Electrical activity Pancreatic β cell Islet of Langerhans 

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Copyright information

© Springer-Verlag 1991

Authors and Affiliations

  • Rosa M. Santos
    • 1
  • Luis M. Rosario
    • 1
  • Angel Nadal
    • 1
  • Javier Garcia-Sancho
    • 2
  • Bernat Soria
    • 1
  • Miguel Valdeolmillos
    • 1
  1. 1.Department of Physiology and Institute of NeurosciencesUniversity of AlicanteAlicanteSpain
  2. 2.Department of Physiology and BiochemistryUniversity of ValladolidValladolidSpain

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