Abnormal aggregation accompanies abnormal platelet Ca2+ handling in arterial thrombosis

Area of Science:

• Cardiovascular Biology
• Hematology
• Cellular Physiology

Background:

• Platelet activation is crucial in arterial thrombosis.
• Calcium ions (Ca2+) play a pivotal role in platelet function.
• Dysregulation of intracellular calcium can lead to hypercoagulable states.

Purpose of the Study:

• To investigate the relationship between resting intracellular calcium levels and platelet aggregation in patients with arterial thrombosis.
• To determine if elevated calcium contributes to the hyper-reactivity of platelets in these patients.

Main Methods:

• Measurement of cytoplasmic Ca2+ using Quin 2 fluorescence.
• Measurement of dense tubular Ca2+ using chlorotetracycline (CTC) fluorescence.
• Turbidimetric studies of platelet-rich plasma (PRP) aggregation stimulated by ADP and collagen.
• Correlation analysis between resting calcium levels and aggregation parameters (Vmax, ED50).
• Experiments using the calcium ionophore A23187 on normal platelets.

Main Results:

• Patients with arterial thrombosis exhibited higher resting cytoplasmic and dense tubular Ca2+ levels compared to normal donors.
• Platelet aggregation rates were increased in patients, particularly for ADP-stimulated aggregation (increased Vmax, decreased ED50).
• Collagen-stimulated aggregation showed decreased ED50 in patients.
• Elevated resting dense tubular Ca2+ levels correlated linearly with observed changes in aggregation parameters.
• Pre-incubation of normal platelets with A23187 mimicked the ADP-stimulated aggregation changes seen in patients.

Conclusions:

• Elevated resting cytoplasmic and dense tubular Ca2+ levels are characteristic of platelets from patients with arterial thrombosis.
• This intracellular calcium dysregulation primes platelets, rendering them hyper-sensitive to physiological stimuli.
• The findings suggest that increased resting calcium is a significant contributing factor to the pathogenesis of arterial thrombosis.