Summary
The monovalent cation ionophores monensin and nigericin cause platelet shape change
at a rate of approximately 1/20 of that caused by ADP. The effect of monensin was
studied further. Shape change caused by monensin is pH dependent, increasing in rate
as extracellular pH increases. Monensin induced shape change is not blocked by 30
μM cinanserin which completely inhibits serotonin induced shape change. Also, the
amount of serotonin secreted by monensin treated platelets is below the threshold
required to induce shape change. 100 μM ATP which inhibits ADP induced shape change
does not affect monensin induced shape change. Amiloride, a sodium transport blocker,
inhibits both the rate of ADP induced shape change and platelet spreading on poly-lysine
coated glass. Amorphous platelet cyto-skeletons isolated from resting platelets at
pH 6.8 with Mg+ + but not Ca++ can be transformed into filament bundles by subsequent incubation at pH 7.6. We conclude
that platelet shape change is at least in part triggered by changes in cellular Na+ and pH
Keywords
Platelet shape change - Sodium - pH