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Related Concept Videos

Voltage-gated Ion Channels01:26

Voltage-gated Ion Channels

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Voltage-gated ion channels are transmembrane proteins that open and close in response to changes in the membrane potential. They are present on the membranes of all electrically excitable cells such as neurons, heart, and muscle cells.
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Ion channels are specialized proteins on the plasma membrane that allow charged ions to pass down their electrochemical gradient. Their main function is to maintain the membrane potential which is critical for cell viability. These channels are either gated or non-gated and can transport more than a thousand ions within milliseconds for the cellular event to occur.
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Ion Channels01:19

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The movement of ions like sodium, potassium, and calcium into and out of the cell is essential to maintain the electrochemical gradient in living cells. The ion channels—a class of membrane transport proteins—help maintain this ionic gradient for the smooth functioning of physiological activities such as maintaining cell size and volume, conducting nerve impulses, and gas and nutrient exchange.
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Junctional membrane permeability : Effects of divalent cations.

G M Oliveira-Castro1, W R Loewenstein

  • 1Cell Physics Laboratory, Department of Physiology, Columbia University College of Physicians and Surgeons, 10032, New York, New York.

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|November 1, 2013
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Summary

Divalent cations like calcium significantly reduce junctional conductance in Chironomus salivary gland cells. This effect, particularly by calcium, impacts cell permeability and can be reversed under specific conditions.

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Area of Science:

  • Cell biology
  • Membrane biophysics
  • Ion channel function

Background:

  • Gap junctions mediate intercellular communication.
  • Divalent cations are known to modulate channel function.

Purpose of the Study:

  • To investigate the effect of divalent cations on junctional conductance and permeability.
  • To determine the potency and mechanism of action of various divalent cations.

Main Methods:

  • Perforation of nonjunctional membrane to expose junctional membranes to controlled media.
  • Varying divalent cation concentrations (Ca++, Mg++, Sr++, Ba++, Mn++).
  • Measurement of junctional conductance and permeability to fluorescein.

Main Results:

  • Junctional conductance significantly decreased by Ca++, Mg++, Sr++, Ba++, and Mn++.
  • Calcium (Ca++) was the most potent, with minimal effective concentration of 4-8x10(-5) M.
  • Calcium also reduced junctional permeability to fluorescein.
  • Depression was localized to directly accessed membranes and was rapid.
  • Reversal of depression was possible in Ca++-free medium but not in 10(-3) M Ca++.
  • Hole sealing observed in the presence of divalent cations.

Conclusions:

  • Divalent cations, especially Ca++, play a critical role in regulating gap junction permeability.
  • The observed effects suggest a direct interaction of Ca++ with junctional channels.
  • Cellular membrane potential influences the cation-induced modulation of junctional conductance.