Cultured chick-embryo heart cells respond differently to ouabain as measured by the increase in their intracellular Na+ concentration.
Using digital imaging microscopy with the sodium-sensitive fluorescent indicator sodium-binding benzofuran isophtalate (SBFI), we examined the cytosolic free sodium ion concentration ([Na+]i) in single chick-embryo heart cells. The distribution of the [Na+]i was homogeneous within one cell, but we found a wide cell to cell variation in the range of 3 to 18 mM [Na+]i. In contrast to former experiments showing a heterogeneity of chick-embryo heart cells with respect to their [Ca2+]i (Ahlemeyer et al. (1992) Eur. J. Biochem. 205, 269-275), we could not distinguish cell populations with different [Na+]i. We found a lognormal distribution of the resting [Na+]i with a median value of 8.8 mM with a standard deviation of 4.5 mM (n = 90). After the addition of varying concentrations of ouabain, we found a biphasic dose-response curve as measured by the increase in [Na+]i. Ouabain showed its half-maximal effect on the [Na+]i between 10(-9) M and 10(-8) M and at 4.3.10(-6) M under steady-state conditions. The finding of a heterogeneity of chick-embryo heart cells with respect to their ouabain-induced increase in [Na+]i is consistent with our previous observations of cells differing in their [Ca2+]i and in the sensitivity of their sodium pumps to cardiac glycosides.
Ahlemeyer
B
B
Institut für Biochemie und Endokrinologie, Justus-Liebig-Universität Giessen, Germany.
Weintraut
H
H
Schoner
W
W
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D007091:Image Processing, Computer-Assisted; D007700:Kinetics; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*
D010042:Ouabain; D012964:Sodium; D002118:Calcium