CIRCUMVENTION OF THE BASSET HOUND HEREDITARY THROMBOPATHY BY PLATELETACTIVATION WITH PHORBOL-MYRISTATE ACETATE

Platelets from dogs with Basset hound hereditary thrombopathy (BHT) ch ange shape but do not aggregate in response to most physiologic agonis ts [adenosine diphosphate (ADP), platelet-activating factor (PAF), col lagen, thromboxane mimetic U46619 plus epinephrine and low concentrati ons of thrombin], Aggregation in response to higher concentrations of thrombin is slow, but irreversible, The responses of normal canine and affected BHT platelets to the nonphysiologic agonist phorbol myristat e acetate (PMA) were investigated, Aggregation of normal canine and af fected platelets by PMA was irreversible and associated with dense gra nule adenosine triphosphate (ATP) secretion, The addition of PMA to [H -3]-arachidonic acid-labelled normal and affected canine platelets had no significant effect on the production of 1,2-diacylglycerol (1,2-DA G). Activation of [P-32]-labelled platelets by PMA was associated with rapid phosphorylation of the 47 kDa substrate of protein kinase C and slow phosphorylation of the 20 kDa myosin light chain in both groups, In affected platelets, there was reduced phosphorylation of a band of approximately 65 kDa, The identity and functional significance of thi s band is not known, This study provides evidence that direct activati on of protein kinase C by PMA in BHT circumvents the dysfunction chara cteristic of Basset hound hereditary thrombopathy and that the defect must exist somewhere at a point in signal transduction prior to activa tion of protein kinase C, We also conclude that normal and affected ca nine platelets possess protein kinase C and a 47 kDa substrate functio n that is similar to human platelets.