on the basis of recent determinations of submicromolar levels of free cytoplasmic ca ( 2+ ) and our initial rates of ( 45 ) ca-labeled ca ( 2+ ) uptake , we show that measurement of the unidirectional influx of ca ( 2+ ) across the plasmalemma is not feasible because the specific activity of the pool of free cytoplasmic calcium increases almost instantaneously to a level that would result in a significant , but unknown , efflux of label .
C0007603
plasmalemma
C0010834
cytoplasmic