title: Functional evidence for intracellular acid extruders in human ventricular myocardium.
abstract: 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.
authors.affiliation: Department of Pharmacology, National Defense Medical Center, Cheng-Hsin General Hospital, Taipei, Taiwan, Republic of China. shloh@ndmctsgh.edu.tw
authors.forename: Shih-Hurng
authors.initials: SH
authors.lastname: Loh
authors.forename: Jong-Shiaw
authors.initials: JS
authors.lastname: Jin
authors.forename: Chien-Sung
authors.initials: CS
authors.lastname: Tsai
authors.forename: Chao-Ming
authors.initials: CM
authors.lastname: Chao
authors.forename: Cheng-Shian
authors.initials: CS
authors.lastname: Chiung
authors.forename: Wei-Hwa
authors.initials: WH
authors.lastname: Chen
authors.forename: Cheng-I
authors.initials: CI
authors.lastname: Lin
authors.forename: Chao-Chin
authors.initials: CC
authors.lastname: Chuang
authors.forename: Jeng
authors.initials: J
authors.lastname: Wei
mesh_terms: 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
chemical_list: 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