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Related Experiment Videos

ATP causes glomus cell [Ca2+]c increase without corresponding increases in CSN activity.

A Mokashi1, J Li, A Roy

  • 1Department of Physiology, School of Medicine, University of Pennsylvania, B400 Richards Building 37th & Hamilton Walk, Philadelphia, PA 19104-6085, USA.

Respiratory Physiology & Neurobiology
|October 2, 2003
PubMed
Summary
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Extracellular ATP increases intracellular calcium in carotid body glomus cells, but higher concentrations inhibit carotid sinus nerve activity, contrary to expectations.

Area of Science:

  • Neuroscience
  • Cell Physiology
  • Biochemistry

Background:

  • The carotid body (CB) is a chemosensory organ crucial for regulating breathing.
  • Intracellular calcium ([Ca(2+)](c)) plays a key role in CB sensory transduction.
  • The precise relationship between [Ca(2+)](c) and carotid sinus nerve (CSN) activity is not fully understood.

Purpose of the Study:

  • To investigate the effect of extracellular ATP on intracellular calcium levels in rat CB glomus cells.
  • To determine the impact of ATP-induced [Ca(2+)](c) changes on afferent CSN activity.

Main Methods:

  • In vitro rat carotid body preparation.
  • Measurement of intracellular calcium using fluorescent indicators.
  • Extracellular application of ATP at various concentrations.

Related Experiment Videos

  • Electrophysiological recordings of CSN activity and glomus cell membrane potential.
  • Pharmacological manipulation using Suramin and cyclopiazonic acid (CPA).

    • Main Results:

    • ATP caused a dose-dependent increase in [Ca(2+)](c), with 2/3 from influx and 1/3 from ER release.
    • Low ATP concentrations (5-10 microM) stimulated CSN activity under normoxia and hypoxia.
    • High ATP concentrations (≥100 microM) initially stimulated but then inhibited CSN activity.
    • ATP-induced glomus cell hyperpolarization and increased outward K+ current were observed at 100 microM ATP.

    Conclusions:

    • ATP-evoked intracellular calcium increases do not linearly correlate with CSN activity.
    • High ATP concentrations may inhibit CSN activity via mechanisms involving K+ currents and hyperpolarization.
    • The study challenges the simple hypothesis linking [Ca(2+)](c) rise directly to enhanced CSN activity.