PMID- 15626700
OWN - NLM
STAT- MEDLINE
DCOM- 20050706
LR  - 20240314
IS  - 0006-3495 (Print)
IS  - 1542-0086 (Electronic)
IS  - 0006-3495 (Linking)
VI  - 88
IP  - 3
DP  - 2005 Mar
TI  - Modulation of Mg2+ efflux from rat ventricular myocytes studied with the 
      fluorescent indicator furaptra.
PG  - 1911-24
AB  - The fluorescent Mg(2+) indicator furaptra (mag-fura-2) was introduced into single 
      ventricular myocytes by incubation with its acetoxy-methyl ester form. The ratio 
      of furaptra's fluorescence intensity at 382 and 350 nm was used to estimate the 
      apparent cytoplasmic [Mg(2+)] ([Mg(2+)](i)). In Ca(2+)-free extracellular 
      conditions (0.1 mM EGTA) at 25 degrees C, [Mg(2+)](i) averaged 0.842 +/- 0.019 
      mM. After the cells were loaded with Mg(2+) by exposure to high extracellular 
      [Mg(2+)] ([Mg(2+)](o)), reduction of [Mg(2+)](o) to 1 mM (in the presence of 
      extracellular Na(+)) induced a decrease in [Mg(2+)](i). The rate of decrease in 
      [Mg(2+)](i) was higher at higher [Mg(2+)](i), whereas raising [Mg(2+)](o) slowed 
      the decrease in [Mg(2+)](i) with 50% reduction of the rate at approximately 10 mM 
      [Mg(2+)](o). Because a part of the furaptra molecules were likely trapped inside 
      intracellular organelles, we assessed possible contribution of the indicator 
      fluorescence emitted from the organelles. When the cell membranes of 
      furaptra-loaded myocytes were permeabilized with saponin (25 microg/ml for 5 
      min), furaptra fluorescence intensity at 350-nm excitation decreased to 22%; thus 
      approximately 78% of furaptra fluorescence appeared to represent cytoplasmic 
      [Mg(2+)] ([Mg(2+)](c)), whereas the residual 22% likely represented [Mg(2+)] in 
      organelles (primarily mitochondria as revealed by fluorescence imaging). [Mg(2+)] 
      calibrated from the residual furaptra fluorescence ([Mg(2+)](r)) was 0.6-0.7 mM 
      in bathing solution [Mg(2+)] (i.e., [Mg(2+)](c) of the skinned myocytes) of 
      either 0.8 mM or 4.0 mM, suggesting that [Mg(2+)](r) was lower than and virtually 
      insensitive to [Mg(2+)](c). We therefore corrected furaptra fluorescence signals 
      measured in intact myocytes for this insensitive fraction of fluorescence to 
      estimate [Mg(2+)](c). In addition, by utilizing concentration and dissociation 
      constant values of known cytoplasmic Mg(2+) buffers, we calculated changes in 
      total Mg concentration to obtain quantitative information on Mg(2+) flux across 
      the cell membrane. The calculations indicate that, in the presence of 
      extracellular Na(+), Mg(2+) efflux is markedly activated by [Mg(2+)](c) above the 
      normal basal level (approximately 0.9 mM), with a half-maximal activation of 
      approximately 1.9 mM [Mg(2+)](c). We conclude that [Mg(2+)](c) is tightly 
      regulated by an Mg(2+) efflux that is dependent on extracellular [Na(+)].
FAU - Tursun, Pulat
AU  - Tursun P
AD  - Department of Physiology, Tokyo Medical University, 6-1-1 Shinjuku-ku, Tokyo 
      160-8402, Japan.
FAU - Tashiro, Michiko
AU  - Tashiro M
FAU - Konishi, Masato
AU  - Konishi M
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
DEP - 20041230
PL  - United States
TA  - Biophys J
JT  - Biophysical journal
JID - 0370626
RN  - 0 (Fluorescent Dyes)
RN  - 120551-15-7 (2-(2-(5-carboxy)oxazole)-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic 
      acid)
RN  - I38ZP9992A (Magnesium)
RN  - TSN3DL106G (Fura-2)
SB  - IM
MH  - Animals
MH  - Cell Membrane/*metabolism
MH  - Cells, Cultured
MH  - Computer Simulation
MH  - Fluorescent Dyes
MH  - *Fura-2/*analogs & derivatives
MH  - Heart Ventricles/cytology/metabolism
MH  - Magnesium/*metabolism
MH  - Male
MH  - Metabolic Clearance Rate
MH  - *Models, Biological
MH  - Myocytes, Cardiac/*metabolism
MH  - Rats
MH  - Rats, Wistar
MH  - Spectrometry, Fluorescence/*methods
PMC - PMC1305244
EDAT- 2005/01/01 09:00
MHDA- 2005/07/07 09:00
PMCR- 2006/03/01
CRDT- 2005/01/01 09:00
PHST- 2005/01/01 09:00 [pubmed]
PHST- 2005/07/07 09:00 [medline]
PHST- 2005/01/01 09:00 [entrez]
PHST- 2006/03/01 00:00 [pmc-release]
AID - S0006-3495(05)73254-9 [pii]
AID - 55517 [pii]
AID - 10.1529/biophysj.104.055517 [doi]
PST - ppublish
SO  - Biophys J. 2005 Mar;88(3):1911-24. doi: 10.1529/biophysj.104.055517. Epub 2004 
      Dec 30.