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A Transmural Gradient in the Cardiac Na/K Pump Generates a Transmural Gradient in Na/Ca Exchange

Journal of Membrane Biology volume 233, pages 51–62 (2010)Cite this article

Abstract

We previously demonstrated a transmural gradient in Na/K pump current (I P) and [Na+] i , with the highest maximum I P and lowest [Na+] i in epicardium. The present study examines the relationship between the transmural gradient in I P and Na/Ca exchange (NCX). Myocytes were isolated from canine left ventricle. Whole-cell patch clamp was used to measure current generated by NCX (I NCX) and inward background calcium current (I ibCa), defined as inward current through Ca2+ channels less outward current through Ca2+-ATPase. When resting myocytes from endocardium (Endo), midmyocardium (Mid) or epicardium (Epi) were studied in the same conditions, I NCX was the same and I ibCa was zero. Moreover, Western blots were consistent with NCX protein being uniform across the wall. However, the gradient in [Na+] i , with I ibCa = 0, should create a gradient in [Ca2+] i . To test this hypothesis, we measured resting [Ca2+] i using two methods, based on either transport or the Ca2+-sensitive dye Fura2. Both methods demonstrated a significant transmural gradient in resting [Ca2+] i , with Endo > Mid > Epi. This gradient was eliminated by exposing Epi to sufficient ouabain to partially inhibit Na/K pumps, thus increasing [Na+] i to values similar to those in Endo. These data support the existence of a transmural gradient for Ca2+ removal by NCX. This gradient is not due to differences in expression of NCX; rather, it is generated by a transmural gradient in [Na+] i , which is due to a transmural gradient in plasma membrane expression of the Na/K pump.

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Acknowledgements

This work was supported by National Institutes of Health grants HL085221, HL28958 and HL67101 and American Heart Association grant 0430307N. We are grateful to Dr. Richard Lin for assistance with the Western blotting.

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  1. Department of Physiology and Biophysics, SUNY at Stony Brook, Stony Brook, NY, 11794-8661, USA

    Wei Wang, Junyuan Gao, Emilia Entcheva, Ira S. Cohen, Chris Gordon & Richard T. Mathias

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  1. Wei Wang
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  2. Junyuan Gao
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  3. Emilia Entcheva
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  4. Ira S. Cohen
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  5. Chris Gordon
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  6. Richard T. Mathias
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Correspondence to Richard T. Mathias.

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Wang, W., Gao, J., Entcheva, E. et al. A Transmural Gradient in the Cardiac Na/K Pump Generates a Transmural Gradient in Na/Ca Exchange. J Membrane Biol 233, 51–62 (2010). https://doi.org/10.1007/s00232-010-9224-y

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  • DOI: https://doi.org/10.1007/s00232-010-9224-y

Keywords

  • Canine heart
  • Left ventricle
  • Isolated myocyte
  • Whole-cell patch clamp
  • Inward background Ca2+ current
  • Fura2-AM
  • Resting [Ca2+] i