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Home / Equine Research Bank / J Physiol / Voltage-dependent calcium currents and cytosolic calcium in ...
The Journal of physiology1996; 492 ( Pt 2)(Pt 2); 347-358; doi: 10.1113/jphysiol.1996.sp021313

Voltage-dependent calcium currents and cytosolic calcium in equine airway myocytes.

Abstract: 1. The relationship between voltage-dependent calcium channel current (I(Ca)) and cytosolic free calcium concentration ([Ca2+]i) was studied in fura-2 AM-loaded equine tracheal myocytes at 35 degrees C and 1.8 mM Ca2+ using the nystatin patch clamp method. The average cytosolic calcium buffering constant was 77 +/- 3 (n = 14), and the endogenous calcium buffering constant component is likely to be between 15 and 50. 2. I(Ca) did not evoke significant calcium-induced calcium release (CICR) since (i)[Ca2+]i scaled with the integrated I(Ca) over the full voltage range of evoked calcium currents, (ii) increases in [Ca2+]i associated with I(Ca) were consistent with cytoplasmic buffering of calcium ions entering through voltage-dependent calcium channels (VDCCs) only, (iii) there was a fixed instantaneous relationship between transmembrane calcium flux (J(Ca)) and the change in cytosolic free calcium concentration (delta [Ca2+]i) during I(Ca), (iv) caffeine (8 mM) triggered 8-fold higher calcium transients than I(Ca), and (v) I(Ca) evoked following release of intracellular calcium by caffeine resulted in an equivalent delta[Ca2+]i-J(Ca) relationship. 3. The time constant (T) for the decay in [Ca2+]i was 8.6 +/- 1.5 s (n = 8) for single steps and 8.6 +/- 1.1 s (n = 13) following multiple steps that increased [Ca2+]i to much higher levels. Following application of caffeine (8 mM), however, [Ca2+]i decay was enhanced (T = 2.0 +/- 0.2 s, n = 3). The rate of [Ca2+]i decay was not voltage dependent, was not decreased in the absence of extracellular Na+ ions, and no pump current was detected. 4. We conclude that under near physiological conditions, neither CICR nor Na(+)-Ca2+ exchange play a substantial role in the regulation of I(Ca)-induced increases in [Ca2+]i, and that, even following release of intracellular calcium by caffeine, Na(+)-Ca2+ exchange does not play an appreciable role in the removal of calcium ions from the cytosol.
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Publication Date: 1996-04-15 PubMed ID: 9019534PubMed Central: PMC1158832DOI: 10.1113/jphysiol.1996.sp021313Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The researchers investigated how voltage-related calcium channels affect the concentration of calcium in the cells that compose the equine trachea. It was found that neither calcium-induced calcium release (CICR) nor sodium-calcium exchange significantly influence these processes.

Investigation into Calcium Current and Concentration

  • The researchers carried out their studies on equine tracheal myocytes, which are muscle cells in the trachea of horses. These cells were loaded with fura-2 AM, a chemical that helps to identify free calcium ions.
  • They used a method called the nystatin patch clamp to investigate the relationship between voltage-dependent calcium channel current, denoted as I(Ca), and the concentration of free calcium ions, represented as [Ca2+]i.
  • Through this method, the scientists identified that the average calcium buffering constant, which is a measure of the cell’s ability to regulate its internal calcium concentration, was approximately 77 with a minor variation of 3. Furthermore, the endogenous calcium buffering constant (related to internal regulation) was estimated to lay between 15 and 50.

Calcium-Induced Calcium Release (CICR)

  • The research showed that I(Ca) was not able to ignite a significant level of CICR. This conclusion was drawn based on several observations such as the scaling of [Ca2+]i with integrated I(Ca) across various voltage values, and equivalence in transmembrane calcium flow (J(Ca)) and change in [Ca2+]i during I(Ca).
  • They also observed that caffeine (8 mM) was able to trigger calcium transients, i.e. temporary increases in intracellular calcium concentration, that were about eight times higher than those induced by I(Ca).
  • Moreover, applying caffeine to induce release of cellular calcium, followed by I(Ca) induction, resulted in an equivalent change in [Ca2+]i and J(Ca).

Time Constant for Calcium Decay

  • The study showed that the time constant (T), which is a measure of the time it takes for [Ca2+]i to decay or decrease, was approximately 8.6 seconds for single steps and for multiple steps that increased [Ca2+]i to much higher levels.
  • The application of caffeine did speed up this decay process, reducing the value of T to around 2.0 seconds.
  • The team observed that the rate of [Ca2+]i decay wasn’t dependent on voltage, was not decreased in the absence of extracellular sodium ions and no detection of pump current was found.

Conclusions of the Study

  • A significant impact of neither CICR nor Na(+)-Ca2+ exchange on the elevation of [Ca2+]i caused by ICa was identified even under near physiological conditions.
  • Additionally, it was found that Na(+)-Ca2+ exchange plays a negligible role in removing calcium ions from the cytosol even after caffeine-induced release of intracellular calcium.

Cite This Article

APA
Fleischmann BK, Wang YX, Pring M, Kotlikoff MI. (1996). Voltage-dependent calcium currents and cytosolic calcium in equine airway myocytes. J Physiol, 492 ( Pt 2)(Pt 2), 347-358. https://doi.org/10.1113/jphysiol.1996.sp021313

Publication

The Journal of physiology
ISSN: 0022-3751
NlmUniqueID: 0266262
Country: England
Language: English
Volume: 492 ( Pt 2)
Issue: Pt 2
Pages: 347-358

Researcher Affiliations

Fleischmann, B K
  • Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104-6046, USA.
Wang, Y X
    Pring, M
      Kotlikoff, M I

        MeSH Terms

        • Animals
        • Buffers
        • Calcium / metabolism
        • Calcium / physiology
        • Calcium Channels / physiology
        • Carrier Proteins / metabolism
        • Cytosol / metabolism
        • Electrophysiology
        • Horses
        • Muscle, Smooth / cytology
        • Muscle, Smooth / metabolism
        • Osmolar Concentration
        • Sodium-Calcium Exchanger
        • Time Factors
        • Trachea / cytology
        • Trachea / metabolism

        Grant Funding

        • HL 45239 / NHLBI NIH HHS

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        Citations

        This article has been cited 15 times.
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