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Related Experiment Videos

Ca2+ induces charybdotoxin-sensitive membrane potential changes in rat lymphocytes.

S Grinstein1, J D Smith

  • 1Division of Cell Biology, Hospital for Sick Children, Toronto, Canada.

The American Journal of Physiology
|August 1, 1989
PubMed
Summary

Calcium-activated potassium channels in lymphocytes are confirmed by charybdotoxin (CTX) inhibition. Moderate calcium increases cause hyperpolarization, while higher levels activate cation channels, explaining prior research discrepancies.

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Area of Science:

  • Immunology
  • Cell Physiology
  • Ion Channel Biology

Background:

  • Discrepancies exist regarding calcium-activated potassium channels in lymphocytes.
  • Previous patch-clamping studies failed to detect these channels, despite evidence of altered membrane potential.

Purpose of the Study:

  • To investigate the presence and function of calcium-activated potassium channels in rat thymic lymphocytes.
  • To clarify the role of these channels in lymphocyte membrane potential regulation.

Main Methods:

  • Utilized charybdotoxin (CTX), a specific inhibitor of calcium-activated potassium channels.
  • Employed fluorescent probes to measure membrane potential (Em) and cytosolic calcium concentration ([Ca2+]i) in ionomycin-treated lymphocytes.

Main Results:

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  • CTX did not affect resting Em, indicating no significant role for these channels at basal calcium levels.
  • Moderate [Ca2+]i elevation induced CTX-sensitive hyperpolarization, dependent on potassium gradients.
  • High [Ca2+]i (>1 microM) resulted in a biphasic response: transient hyperpolarization followed by sodium-dependent depolarization, attributed to nonselective cation channels.

Conclusions:

  • Rat thymic lymphocytes possess calcium-activated potassium channels activated by moderate calcium increases, causing hyperpolarization.
  • At higher calcium concentrations, nonselective cation channels dominate, leading to depolarization.
  • Observed effects reconcile previous conflicting findings on lymphocyte membrane potential changes.