Isolation of mouse megakaryocytes. II. Functional and metabolic aspects of two different maturational stages.

Functional and metabolic parameters were compared in immature and mature megakaryocytes (MK) isolated from bone marrow of the mouse by Percoll density gradient centrifugation. Comparison of metabolic parameters revealed that the ability to take up serotonin was equal in both megakaryocytic fractions. The uptake of radioactively labeled adenine was increased in immature MK as compared with mature MK. Total adenosine triphosphate (ATP) content was enhanced during the differentiation from MK to platelets: immature MK: 5, mature MK: 29, platelets: 63 nmol ATP/mg protein. Since MK, like platelets, released ATP upon stimulation, thrombin-induced release was used as functional parameter to differentiate between secretable and non-secretable ATP compartments. Upon thrombin stimulation both MK fractions released about 25% of their total ATP as compared with about 40% secreted by platelets. Although the actual size of the non-secretable ATP pool was different in mature MK and platelets, they demonstrated similar percentages of retained ATP (20-25%) in contrast to a much higher retention (62%) by immature MK. The present findings suggest that the bulk of ATP is acquired by immature MK as they gain maturity, although some ATP is still obtained during even later stages of differentiation. This growing ATP pool could be attributed mainly to the enlargement of the secretable compartment during the transition of immature MK to mature MK.