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Am J Physiol Heart Circ Physiol (May 15, 2003). doi:10.1152/ajpheart.00277.2003
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Submitted on March 27, 2003
Accepted on May 7, 2003

Intracellular proton mobility and buffering power in cardiac ventricular myocytes from rat, rabbit and guinea-pig

Massimiliano Zaniboni1, Pawel Swietach2, Alessandra Rossini1, Taku Yamamoto3, Kenneth W. Spitzer3, and Richard D. Vaughan-Jones2*

1 Burdon Sanderson Cardiac Science Centre, University Laboratory of Physiology, Oxford, Oxfordshire, United Kingdom; Dipartimento di Biologia Evolutiva e Funzionale, University of Parma, Parma, Italy
2 Burdon Sanderson Cardiac Science Centre, University Laboratory of Physiology, Oxford, Oxfordshire, United Kingdom
3 Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, Utah, USA

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

Intracellular pH is an important modulator of cardiac function. The spatial regulation of pH within cytoplasm will depend, in part, on the intracellular H+-ion mobility. The apparent diffusion coefficient for intracellular H+, DHapp, was estimated in single ventricular myocytes isolated from rat, guinea-pig and rabbit. DHapp was derived by best-fitting predictions of a two-dimensional model of H+-diffusion to the local rise of intracellular [H+], recorded confocally (ratiometric SNARF fluorescence) downstream from an acid-filled, whole-cell patch-pipette. Under CO2/HCO3--free conditions, DHapp was similar in all three species (mean values 8-12.5 x 10-7cm2/s), and was over 200-fold lower than that for H+ ions in water. In guinea pig myocytes, DHapp was increased 2.5 fold in the presence of CO2/HCO3- buffer, in agreement with previous observations in rabbit myocytes. H+i-mobility is therefore low in cardiac cells, a feature that may predispose them to the generation of pHi gradients in response to sarcolemmal acid/base transport or local cytoplasmic acid production. Low H+i-mobility most likely results from H+-shuttling among cytoplasmic mobile and fixed buffers. This hypothesis was explored by comparing the pHi-dependence of intrinsic, intracellular buffering capacity, measured for all three species, and subdividing buffering into mobile and fixed fractions. The proportion of buffer that is mobile will be the main determinant of DHapp. At a given pHi, this proportion appeared to be similar in all three species, consistent with a common value for DHapp. Over the pHi range 6.0-8.0, the proportion is expected to change, predicting that DHapp may display some pHi sensitivity.




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