vanadateactivated calcium influx in a431 cells is dependent on the plasma membrane potential vanadate can activate the uptake of ca in a431 epidermal carcinoma cells by two to fivefold with no detectable lag period preincubation with epidermal growth factor egf to downregulate the egf receptor prevents subsequent stimulation by egf but not that by vanadate ca uptake is sodiumindependent and is not activated by depolarization in high kcl on the contrary vanadatestimulated uptake is completely inhibited by decreasing the plasma membrane potential from about 65 to 30 mv these results demonstrate that the egf receptor is not itself functioning as a ca channel that vanadate is not acting at the level of egf receptor and that the ca transport system exhibits an unusual potential sensitivity in that it is inhibited by depolarization of the plasma membrane