Lead Enters Bovine Adrenal Medullary Cells Through Calcium Channels

Abstract

Agents that stimulate secretion also accelerate the rate of Pb uptake into adrenal medullary cells. For example, when cells are suspended in a medium containing 5 μM Pb²⁺, depolarization by 77 mM K increases the rate of Pb uptake from 12 ± 1 to 47 ± 5 μmol/(L cells × min). K-induced Pb uptake has an apparent K_m for Pb²⁺ of 2.6 μM, and is antagonized by Ca²⁺ with a K_0.5 of 1.4 mM. The Ca channel blocker D-600 inhibits Pb entry with a K_0.5 of 0.4 μM. Pb uptake is also stimulated by the Ca channel agonist BAY K 8644. These observations suggest that Pb passes through Ca channels. The permeability of the channels to Pb appears to be at least 10 times the permeability to Ca.