Intracellular pH regulatory mechanism in human atrial myocardium: functional evidence for Na(+)/H(+) exchanger and Na(+)/HCO(3)(-) symporter.
Intracellular pH (pH(i)) exerts considerable influence on cardiac contractility and rhythm. Over the last few years, extensive progress has been made in understanding the system that controls pH(i) in animal cardiomyocytes. In addition to the housekeeping Na(+)-H(+) exchanger (NHE), the Na(+)-HCO(3)(-) symporter (NHS) has been demonstrated in animal cardiomyocytes as another acid extruder. However, whether the NHE and NHS functions exist in human atrial cardiomyocytes remains unclear. We therefore investigated the mechanism of pH(i) recovery from intracellular acidosis (induced by NH(4)Cl prepulse) using intracellular 2',7'-bis(2-carboxethyl)-5(6)-carboxy-fluorescein fluorescence in human atrial myocardium. In HEPES (nominally HCO(3)(-)-free) Tyrode solution, pH(i) recovery from induced intracellular acidosis could be blocked completely by 30 microM 3-methylsulfonyl-4-piperidinobenzoyl, guanidine hydrochloride (HOE 694), a specific NHE inhibitor, or by removing extracellular Na(+). In 3% CO(2)-HCO(3)(-) Tyrode solution, HOE 694 only slowed the pH(i) recovery, while addition of HOE 694 together with 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (an NHS inhibitor) or removal of extracellular Na(+) inhibited the acid extrusion entirely. Therefore, in the present study, we provided evidence that two acid extruders involved in acid extrusion in human atrial myocytes, one which is HCO(3)(-) independent and one which is HCO(3)(-) dependent, are mostly likely NHE and NHS, respectively. When we checked the percentage of contribution of these two carriers to pH(i) recovery following induced acidosis, we found that the activity of NHE increased steeply in the acid direction, while that of NHS did not change. Our present data indicate for the first time that two acid extruders, NHE and NHS, exist functionally and pH(i) dependently in human atrial cardiomyocytes.
Loh
Shih-Hurng
SH
Department of Pharmacology, National Defense Medical Center, Taipei, Taiwan, ROC. shloh@ndmctsgh.edu.tw
Chen
Wei-Hwa
WH
Chiang
Cheng-Hsien
CH
Tsai
Chien-Sung
CS
Lee
Guo-Chen
GC
Jin
Jong-Shiaw
JS
Cheng
Tzu-Hurng
TH
Chen
Jin-Jer
JJ
D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D006146:Guanidines / Q000494:pharmacology; D006531:HEPES / Q000737:chemistry; D006325:Heart Atria / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000378:metabolism; D007552:Isotonic Solutions / Q000737:chemistry; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology
D005452:Fluoresceins; D005456:Fluorescent Dyes; D006146:Guanidines; D007527:Isoenzymes; D007552:Isotonic Solutions; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C037692:Tyrode's solution; C069139:growth factor-activatable Na-H exchanger NHE-1; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D006531:HEPES