Pancreatic acinar cells: effects of lanthanum ions on amylase release and calcium ion fluxes

The effect of La³⁺ on amylase release and Ca²⁺ fluxes in mouse pancreatic fragments in vitro was studied. Amylase release was increased by 0.1 mM La³⁺ and progressively inhibited by 1.0-10 mM La³⁺. Non stimulated and bethanecol stimulated secretion were altered in an identical manner. Inhibition of amylase release was rapid and reversible. Uptake of ⁴⁵Ca²⁺ was multiphasic with equilibrium with stable Ca²⁺ still not complete after 2 hr. La³⁺ (10 mM) limited uptake of ⁴⁵Ca²⁺ to the extracellular space and slightly decreased total Ca²⁺ content. Lower concentrations of La³⁺ affected ⁴⁵Ca²⁺ uptake and total Ca²⁺ content in a biphasic manner which paralleled effects on amylase release. La³⁺ restricted washout of ⁴⁵Ca²⁺ to isotope in the extracellular space and abolished the bethanecol stimulated increase in ⁴⁵Ca²⁺ efflux. Uptake of ⁴⁵Ca²⁺ into intracellular space, as measured by the 'lanthanum' method, was not affected by bethanecol. Tissue ultrastructure and Na⁺ and K⁺ content were not affected by La³⁺. It is concluded that an influx of extracellular Ca²⁺ is not important for triggering of secretion and that La³⁺ may inhibit amylase release by acting on the release process rather than on Ca²⁺ influx.