Barium-evoked release of catecholamines from digitonin-permeabilized adrenal medullary cells

We investigated the release of catecholamines by barium (Ba) in digitonin-permeabilized bovine adrenal medullary cells, to find out whether Ba acts directly or through the mobilization of endogenous calcium (Ca). We also tried to ascertain whether the release of catecholamines from the permeabilized cells occurs in the same manner as from the non-permeabilized control cells. In the permeabilized cells, a rise in either free Ca or Ba caused a saturable release of catecholamines. The maximal release of catecholamines caused by Ba was greater than that caused by Ca, suggesting that Ba directly triggered the release process. Release of catecholamines by Ba was accompanied by the release of dopamine beta-hydroxylase, both in the permeabilized and control cells, showing that Ba causes an exocytotic release of catecholamines. The concentration of Ba which was required for the release of catecholamines in the permeabilized cells agreed with that required in control cells. We conclude that Ba can substitute Ca in triggering the exocytotic release of catecholamines from the adrenal medullary cells. Permeabilized cells provide accurate information on the direct action of Ba in these cells.