Circumvention of the basset hound hereditary thrombopathy by platelet activation with phorbol myristate acetate.
Platelets from dogs with Basset hound hereditary thrombopathy (BHT) change shape but do not aggregate in response to most physiologic agonists [adenosine diphosphate (ADP), platelet-activating factor (PAF), collagen, thromboxane mimetic U46619 plus epinephrine and low concentrations 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 myristate acetate (PMA) were investigated. Aggregation of normal canine and affected platelets by PMA was irreversible and associated with dense granule adenosine triphosphate (ATP) secretion. The addition of PMA to [(3)H]-arachidonic acid-labelled normal and affected canine platelets had no significant effect on the production of 1,2-diacylglycerol (1,2-DAG). Activation of [(32)P]-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 this band is not known. This study provides evidence that direct activation of protein kinase C by PMA in BHT circumvents the dysfunction characteristic of Basset hound hereditary thrombopathy and that the defect must exist somewhere at a point in signal transduction prior to activation of protein base C. We also conclude that normal and affected canine platelets possess protein kinase C and a 47 kDa substrate function that is similar to human platelets.
Department of Pathology, Michigan State University, East Lansing, Michigan, USA.
M F
MF
McConnell
J S
JS
Thomas
M N
MN
Dipinto
T G
TG
Bell