Functional evidence for intracellular acid extruders in human ventricular myocardium.
Intracellular pH (pH(i)) is a major homeostatic system within the cell. Changes in pH(i) exert great influence on cardiac contractility and rhythm. Both the housekeeping Na+ - H+ exchanger (NHE) and the Na+ - HCO3- symporter (NHS) have been confirmed as major transporters for the active acid extrusion mechanism in animal cardiomyocytes. However, whether the NHE and NHS functionally coexist in human ventricular cardiomyocytes remains unclear. We therefore examined the mechanism of pH(i) recovery following an NH4Cl-induced intracellular acidosis in the human ventricular myocardium. The pH(i) was monitored by microspectrofluorimetry by the use of intracellular 2',7'-bis(2-carboxyethyl)-5(6)-carboxy-fluorescein (BCECF)-fluorescence. HOE 694 (30 microM), a specific NHE inhibitor could block pH(i) recovery from induced intracellular acidosis completely in nominally HCO3- -free HEPES Tyrode solution, but it only partially inhibited the pH(i) recovery in 5% CO2/HCO3- Tyrode solution. In 5% CO2/HCO3- Tyrode solution, the addition of HOE 694 together with DIDS (an NHS inhibitor) or the removal of [Na+](o) could entirely inhibit the acid extrusion. We conclude for the first time that two different acid extruders, HCO3- -independent and -dependent, were most likely the NHE and NHS, respectively, that functionally coexisted in the human ventricular cardiomyocytes.
Loh
Shih-Hurng
SH
Department of Pharmacology, National Defense Medical Center, Cheng-Hsin General Hospital, Taipei, Taiwan, Republic of China. shloh@ndmctsgh.edu.tw
Jin
Jong-Shiaw
JS
Tsai
Chien-Sung
CS
Chao
Chao-Ming
CM
Chiung
Cheng-Shian
CS
Chen
Wei-Hwa
WH
Lin
Cheng-I
CI
Chuang
Chao-Chin
CC
Wei
Jeng
J
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000143:Acids / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism; D005260:Female; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006146:Guanidines / Q000494:pharmacology; D006352:Heart Ventricles; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013450:Sulfones / Q000494:pharmacology
D000143:Acids; D001639:Bicarbonates; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006146:Guanidines; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C074107:3-methylsulfonyl-4-piperidinobenzoyl guanidine; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid