Specific inhibition of a calcium dependent activation of brain cyclic AMP phosphodiesterase activity by vinblastine

Vinblastine selectively inhibits the activation of brain cyclic AMP phosphodiesterase activity by Ca++-protein activator (50% inhibition by 2 x 10(-5) M). This inhibitory effect was reversed by excessive amounts of the activator, whereas large quantities of Ca++ caused only a slight suppression of the vinblastine effect. This result of vinblastine suggests a new site of its action and also suggests the possible role of protein activator, phosphodiesterase proteins or cyclic nucleotides in the previously known effects of vinblastine in vivo and in vitro.