Summary
The role of membrane potential in the activation of human platelets by thrombin, ADP
and PAF was assessed, using the fluorescent probe diSC3(5). Thrombin, ADP and PAF transiently depolarised the platelet membrane by 6-8 mV from
its resting level (—70 mV). This depolarisation had a similar time course to that
of shape change. The ionophores valinomycin and gramicidin hyperpolarised and depolarised
the platelets respectively but did not activate them. In contrast, exposure of platelets
to high K+ media both depolarised and caused them to change shape. Removal of Na+ from the suspension media abolished the depolarisation induced by thrombin, ADP and
PAF but the platelets under these conditions were still capable of changing shape
and aggregating. This result indicates that the observed depolarisation depends on
Na+ fluxes. Amiloride or tetrodotoxin did not mimic the effect of Na+ removal suggesting that any Na+ movement involved does not go through the classic “Na+ channel”. Thrombin, ADP and PAF still depolarised the platelet membrane in the absence
of added Ca+
+. Under these conditions, however, the membrane did not repolarise. It is evident
that all three agents, thrombin, ADP and PAF, change the membrane potential of human
washed platelets through a similar mechanism and this change seems to be a consequence
of stimulus-receptor interaction (and platelet activation?). A causal relationship
however between these events cannot be clearly shown.
Keywords
Platelet activation - Tissue plasminogen activator - Membrane potential - Fluorescent
dye Summary
