AJP - Cell Physiology, Vol 234, Issue 5 139-C145, Copyright © 1978 by American Physiological Society
Effect of lanthanum and reduced temperature on 45Ca efflux from rabbit aorta
R. C. Deth
The ability of lanthanum (La3+) to block calcium efflux from smooth muscle
cells of the rabbit aorta has been examined. La3+ promotes the very early
phase of 45Ca efflux, which is extracellular in origin, and partially
inhibits the latter, cellular portion. Stimulation of 45Ca efflux caused by
the release of intracellular 45Ca with either 10(-4) M dinitrophenol or 10
mM caffeine was not reduced by pretreatment with 10 mM La for 40 min,
whereas stimulation due to norepinephrine was abolished. It was concluded
that during the use of the "La method" for measuring cellular 45Ca there is
an underestimation due to unblocked 45Ca loss. This loss can be reduced by
processing tissue at 2 degrees C, which inhibits transport processes. The
time course of 45Ca uptake and the stimulation of uptake by high K+ are
qualitatively but not quantitatively similar if tissues are washed at 37
and 2 degrees C. Tissues washed in La3+ at 2 degrees C for 60 min retain
approximately double the cellular 45Ca of those washed at 37 degrees C.
This methodology provides an improved correlation between estimates of
cellular calcium derived from 45Ca uptake and 45Ca efflux experiments.
