EFFECTS OF INTRACELLULAR ADMINISTRATION OF L-TYROSINE AND L-PHENYLALANINE ON VOLTAGE-OPERATED CALCIUM CONDUCTANCE IN PC12 PHEOCHROMOCYTOMA CELLS

Changes induced by internal administration of L-tyrosine and L-phenylalanine in high-threshold calcium currents have been studied on perfused PC12 pheochromocytoma cells using whole-cell voltage-clamp technique. A method for rapid changes of perfusing solutions has been used. L-Tyrosine (20-mu-M) slowed down the decline ('wash-out') of I(Ca) occuring during intracellular perfusion and in most cells induced its temporary recovery. Alpha-Methyl-D,L-tyrosine (a tyrosine hydroxylase blocker) exerted a similar effect. On the other hand, L-phenylalanine (20-mu-M) in most cells speeded-up the decline of I(Ca). Replacement of ATP in the perfusing solution by an equivalent amount of ADP (2 mM) did not alter the effects of amino acids. The possible mechanisms of the described changes are discussed in connection with the known role of L-tyrosine in posttranslational modifications of microtubular proteins.