Subsecond calcium dynamics in ADP- and thrombin-stimulated platelets: a continuous-flow approach using indo-1

Area of Science:

• Hematology
• Cellular Physiology
• Biophysics

Background:

• Cytosolic calcium ([Ca2+]i) dynamics are crucial for platelet function.
• Understanding platelet calcium regulation under physiological blood flow is essential.

Purpose of the Study:

• To investigate the kinetics and regulation of [Ca2+]i changes in human platelets under physiological blood flow.
• To compare the effects of adenosine diphosphate (ADP) and thrombin on platelet calcium signaling.

Main Methods:

• Utilized a novel continuous-flow system with indo-1-loaded human platelets.
• Measured [Ca2+]i changes in response to ADP and thrombin stimulation.
• Assessed platelet aggregation using single-particle counting.

Main Results:

• Both ADP and thrombin rapidly increased [Ca2+]i within 0.5 seconds under physiological flow.
• ADP triggered a transient [Ca2+]i peak (1-2 µmol/L) around 2 seconds.
• Thrombin elicited a sustained and larger [Ca2+]i response.
• The initial phase of [Ca2+]i increase was independent of extracellular calcium, while the subsequent phase was dependent.
• Platelet aggregation kinetics were unaffected by indo-1 loading.

Conclusions:

• Platelet activation by ADP and thrombin involves rapid cytosolic calcium mobilization under physiological flow.
• Distinct kinetic patterns of [Ca2+]i changes are observed between ADP and thrombin stimulation.
• Extracellular calcium plays a significant role in the sustained phase of agonist-induced calcium signaling in platelets.