Interactions between benzylamiloride and fura-2: studies in vitro and in cardiac myocytes.
Amiloride derivatives are commonly used inhibitors of Na+/H+- and Na+/Ca2+-exchange. Because they are fluorescent molecules the use of benzylamiloride (BZA), an inhibitor of Na+/Ca2+ exchange, in conjunction with Fura-2, a commonly used fluorescent Ca2+ indicator, might complicate interpretation of fluorescence data obtained. In vitro data show that BZA decreases the Fura-2 fluorescence at all useful wavelengths in a concentration-dependent manner. The Fura-2 ratio 340/380 (used to estimate intracellular Ca2+ ([Ca2+]in)) also decreased with increasing BZA concentrations. The Stern-Volmer relation suggests that this phenomenon is due to either static or dynamic quenching. Varying temperatures from 4 to 37 degreesC did not alter Stern-Volmer constants, consistent instead with fluorescence resonance energy transfer (FRET). The in situ relevance of these interactions was evaluated in adult rat cardiac myocytes which exhibit Na+/Ca2+ exchange reflected by rapid [Ca2+]in increase following Na+ removal. Pretreatment with BZA >/= 25 microM decreased the magnitude of Fura-2 changes induced by Na+ removal. Analysis of the individual Fura-2 useful wavelengths indicated that >/= 25 microM BZA altered the Fura-2 signal in a manner consistent with the quenching effects noted in vitro. Together, these data show that BZA interacts with Fura-2 in vitro and in situ and suggest caution when interpreting Fura-2 fluorescence data derived in conjunction with BZA.
Hudson
C A
CA
Department of Physiology, Department of Internal Medicine, Texas Tech University Health Sciences Center, 3601 4th Street, Lubbock, Texas, 79430, USA.
Rojas
J D
JD
Sarvazyan
N
N
Wesson
D E
DE
Martínez-Zaguilán
R
R
D000584:Amiloride / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D003627:Data Interpretation, Statistical; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005454:Fluorescence Polarization / Q000706:statistics & numerical data; D016257:Fura-2 / Q000737:chemistry* / Q000378:metabolism; D009206:Myocardium / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013050:Spectrometry, Fluorescence / Q000706:statistics & numerical data
D000584:Amiloride; D016257:Fura-2