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Biophys. J. BioFAST: First Published January 14, 2005. doi:10.1529/biophysj.104.051391
© 2005 by the Biophysical Society.

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CELL BIOPHYSICS

Experimental Generation and Computational Modeling of Intracellular pH Gradients in Cardiac Myocytes

Pawel Swietach 1, Chae-Hun Leem 2, Kenneth W Spitzer 3 and Richard D Vaughan-Jones 4*

1 Oxford University
2 University of Ulsan College of Medicine
3 University of Utah
4 University of Oxford

* To whom correspondence should be addressed. E-mail: richard.vaughan-jones{at}physiol.ox.ac.uk.

Submitted on August 17, 2004
Revised on October 24, 2004
Accepted on 10 January 2005


  Abstract
It is often assumed that pHi is spatially uniform within cells. A double-barreled microperfusion-system was used to apply solutions of weak acid (acetic acid, CO2) or base (ammonia) to localized regions of an isolated ventricular myocyte (guinea-pig). A stable, longitudinal pHi-gradient (up to 1 pHi-unit) was observed (using confocal-imaging of SNARF-1 fluorescence). Changing the fractional exposure of the cell to weak acid/base altered the gradient, as did changing the concentration and type of weak acid/base applied. A diffusion-reaction computational model accurately simulated this behavior of pHi. The model assumes that H+i-movement occurs via diffusive-shuttling on mobile buffers, with little free H+-diffusion. The average diffusion-constant for mobile buffer was estimated as 33x10-7 cm2/s, consistent with an apparent H+i diffusion-coefficient, DHapp, of 14.4x10-7 cm2/s (at pHi 7.07), a value two orders-of-magnitude lower than for H+ ions in water, but similar to that estimated recently from local acid-injection via a cell-attached glass micropipette. We conclude that, because H+i-mobility is so low, an extracellular concentration gradient of permeant weak acid readily induces pHi non-uniformity. Similar concentration gradients for weak acid (e.g. CO2) occur across border-zones during regional myocardial ischemia, raising the possibility of steep pHi-gradients within the heart under some pathophysiological conditions.

Key Words: Diffusion, heart, myocytes, pH-gradients, pH-regulation




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Copyright © 2005 by the Biophysical Society.