Abstract
A comparison of the effectiveness of the trivalent cation, lanthanum (La 3+) relative to Ca 2+ in causing adrenaline and noradrenaline release from bovine adrenal medullary chromaffin cells has been made. In cells maintained in tissue culture and permeabilised with digitonin, both La 3+ and Ca 2+ triggered catecholamine release. La 3+ was more effective than Ca 2+: the EC 50 for La 3+ was shifted to the left of that for Ca 2+ by close to one order of magnitude for both adrenaline and noradrenaline. With respect to adrenaline, the same maximal release was triggered by the two cations, but with respect to noradrenaline, La 3+ triggered a significantly greater release than did Ca 2+. Mixtures of experimental media containing both La 3+ and Ca 2+ caused release of adrenaline and noradrenaline in amounts that approximated closely the sum of the releases caused by Ca 2+ and La 3+ alone. The data strongly imply that either the release mechanisms for adrenaline and for noradrenaline from their respective chromaffin cells are different, or the cellular mechanisms that regulate release from the two cells are different.
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