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Originally published as Biophys J. BioFAST on January 14, 2005.
doi:10.1529/biophysj.104.051391
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Biophysical Journal 88:3018-3037 (2005)
© 2005 The Biophysical Society

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

Pawel Swietach *, Chae-Hun Leem {dagger}, Kenneth W. Spitzer {ddagger} and Richard D. Vaughan-Jones *

* Burdon Sanderson Cardiac Science Centre, University Laboratory of Physiology, Oxford OX1 3PT, United Kingdom; {dagger} Department of Physiology, University of Ulsan College of Medicine, Seoul 138-040, Korea; and {ddagger} Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, Utah 84112 USA

Correspondence: Address reprint requests to Richard D. Vaughan-Jones, E-mail: richard.vaughan-jones{at}physiol.ox.ac.uk.

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 movement occurs via diffusive shuttling on mobile buffers, with little free H+ diffusion. The average diffusion constant for mobile buffer was estimated as 33 x 10–7 cm2/s, consistent with an apparent diffusion coefficient, , of 14.4 x 10–7 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 mobility is so low, an extracellular concentration gradient of permeant weak acid readily induces pHi nonuniformity. 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.




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