Dependence of XXXX accumulation on membrane potential in cultured @entity1 fibroblasts.

@entity1 @entity8331 @entity9942 @entity534 @entity36958 @entity369 @entity19713
The cell-to-medium distribution ratios at steady state of @entity534 ( @entity19713 ) and of the lipid-soluble cation @entity36958 (RTPP) were studied as a function of the membrane potential (Em) in adult @entity1 fibroblasts. The relationship between @entity19713 and Em was qualitatively similar to that of RTPP and Em. Quantitatively, @entity19713 and RTPP differed in that 1) RTPP was much greater than @entity19713 when Em was near zero, indicating a significant binding component in the uptake of @entity8331 + but not of @entity534 , and 2) after a correction for binding when Em is near zero, RTPP was still greater than @entity19713 so that RT/F . ln RTPP exceeded RT/F . ln @entity19713 by 10-25 mV. The pattern of the redistribution of accumulated @entity8331 + and @entity369 after an alteration of Em was identical. In null-point experiments, the external [K+] for which there were no changes in cellular @entity8331 + or @entity534 in the presence of high @entity9942 (the null points) were very similar for the two probes. Em calculated from the null-point measurements (-70(-)-80 mV) was also very similar to RT/F . ln @entity19713 and thus smaller than RT/F.ln RTPP. It was concluded that 1) there was an additional @entity8331 + binding as cellular [ @entity8331 ] rose in response to more negative membrane potentials, 2) the transport system for @entity534 in these cells (system y+) operates as a facilitated diffusion system driven by the membrane potential, and 3) in some circumstances, @entity534 could be employed as a probe of Em.
