© 2004 by European Society of Cardiology
Copyright © 2004, European Society of Cardiology
Endocardial endothelium modulates subendocardial pHi of rabbit papillary muscles: role of transendothelial HCO3– transport
Department of Pharmacology, University of Antwerp, Groenenborgerlaan 171, Antwerp B-2020, Belgium
* Corresponding author. Tel.: +32-3-820-2587; fax: +32-3-265-3276. Email address: paul.fransen{at}ua.ac.be lamberts{at}physiol.med.vu.nl
Objective: This study investigated whether endocardial endothelial cells contribute to intracellular pH (pHi) regulation of subjacent cardiomyocytes. Methods: Right ventricular rabbit papillary muscles were loaded with the pH-sensitive dye 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF-AM) to measure pHi and HCO3– equivalent influx or efflux in muscles with intact endocardial endothelium (+EE) and in muscles with the endocardial endothelium removed (–EE). Results: In steady-state conditions, pHi was consistently higher in +EE than in –EE muscles (7.38±0.03, n=39 vs. 7.27±0.04, n=20, p<0.05). In +EE muscles, removal of HCO3– from the buffer solution or adding 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of HCO3– transport, reduced pHi from 7.38 to 7.24±0.06 (n=14) and to 7.16±0.10 (n=10), respectively, whereas in –EE muscles pHi decreased slightly from 7.27 to 7.15±0.05 (n=14) and to 7.13±0.04 (n=7). In addition, HCO3– equivalent efflux during alkali loads by NH4Cl pulses was smaller in +EE muscles than in –EE muscles (0.89±0.50 vs. 1.99±0.12 mmol/l/min, n=5, p<0.05) and was inhibited by DIDS. HCO3– equivalent influx during recovery from acid load imposed upon wash out of NH4Cl, was larger in +EE muscles than in –EE muscles (2.15±0.54 mmol/l/min, n=6, vs. 1.06±0.20 mmol/l/min, n=5). 5-(N-Ethyl-N-isopropyl)amiloride (EIPA), an inhibitor of Na+/H+ exchange, decreased HCO3– equivalent influx by 50% in both muscle groups but influx was still significantly higher in +EE than in –EE muscles (1.18±0.23 vs. 0.57±0.07 mmol/l/min, p<0.05). Finally, endocardial endothelial cells cultured on collagen-coated inserts established a DIDS-sensitive transendothelial HCO3–gradient. Conclusion: These data suggest that the endocardial endothelium maintains transendothelial fluxes of HCO3– from luminal (blood) to basal (muscle) side of the cells, which modulate pHi regulation in subjacent cardiomyocytes.
KEYWORDS Endothelial function; Acidosis; Ion exchangers; Ion transport; Na/H exchanger
1 Present address: Laboratory for Physiology, VU University Medical Center, Van der Boechorststraat 7, Amsterdam 1081 BT, The Netherlands.
Time for primary review 35 days
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