Regulation of [Na+]i and [Ca2+]i in guinea pig myocytes: dual loading of fluorescent indicators SBFI and fluo 3.
To investigate the mechanisms regulating intracellular Na+ and Ca2+ concentrations ([Na+]i and [Ca2+]i, respectively), we monitored both ion concentrations simultaneously using fluorescent probes, Na(+)-binding benzofuran isophthalate (SBFI) and fluo 3, in unstimulated guinea pig ventricular myocytes. After the addition of 500 microM strophanthidin, [Na+]i increased gradually from 6.6 +/- 0.6 to 20.1 +/- 1.6 mM (mean +/- SE) at 50 min. [Ca2+]i, expressed as the percentage change of corrected fluo 3 fluorescence, was kept at the low level during the first 20 min and then began to increase to 447 +/- 81% of the control at 50 min. The addition of 1 microM hexamethylene amiloride prevented the increases in both [Na+]i and [Ca2+]i. The perfusion of Ca(2+)-free solution or 5 mM Ni(2+)-containing solution suppressed the increase in [Ca2+]i. In cells that exhibited spontaneous contractile activities, [Ca2+]i increased further than that in quiescent cells, whereas [Na+]i levels were similar. In the presence of 1 microM ryanodine, both the spontaneous contractile activities and the further increase in [Ca2+]i were eliminated. These findings indicated that 1) the pathway of Na+ entry was mainly through Na(+)-H+ exchange and that the elevated [Na+]i induced Ca2+ entry mediated by the reverse mode of Na(+)-Ca2+ exchange, and 2) the entered Ca2+ triggered the ryanodine-sensitive Ca2+ release from the sarcoplasmic reticulum, causing the dissociation in the relationship between [Na+]i and [Ca2+]i.
Satoh
H
H
Third Department of Internal Medicine, Hamamatsu University School of Medicine, Japan.
Hayashi
H
H
Noda
N
N
Terada
H
H
Kobayashi
A
A
Hirano
M
M
Yamashita
Y
Y
Yamazaki
N
N
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000814:Aniline Compounds; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004988:Ethers, Cyclic; D005260:Female; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D007700:Kinetics; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009532:Nickel / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D013050:Spectrometry, Fluorescence / Q000379:methods; D013327:Strophanthidin / Q000494:pharmacology*; D014966:Xanthenes
D000814:Aniline Compounds; D001572:Benzofurans; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; D014966:Xanthenes; C061665:sodium-binding benzofuran isophthalate; C057360:5-(N,N-hexamethylene)amiloride; C059715:Fluo-3; D013327:Strophanthidin; D000584:Amiloride; D009532:Nickel; D012964:Sodium; D002118:Calcium