Changes in platelet response to adenosine 5'-diphosphate caused by verapamil

Area of Science:

• Pharmacology
• Cardiovascular Medicine
• Hematology

Background:

• Verapamil is a calcium channel blocker used for coronary artery disease.
• Its effects on vascular smooth muscle are well-established.
• Previous studies on verapamil's impact on platelet function used high concentrations not relevant in vivo.

Purpose of the Study:

• To investigate the influence of low-dose verapamil on platelet response to adenosine diphosphate (ADP).
• To examine verapamil's effect on fibrinogen receptor expression and calcium signaling in platelets.

Main Methods:

• In vitro studies using platelet-rich plasma (PRP) with low verapamil concentrations (0.1-1.0 microM) and ADP.
• Analysis of fibrinogen receptor expression on platelets from patients (n=21) treated with therapeutic verapamil doses (240 mg/day).
• Measurement of calcium ion release and influx in verapamil-pretreated platelets upon ADP activation.

Main Results:

• Low-dose verapamil (0.1 microM) inhibited ADP-evoked platelet aggregation by 10%, with potentiation by prolonged preincubation.
• Therapeutic verapamil doses significantly reduced platelet fibrinogen receptors (from 75,000 to 40,000 per platelet, p < 0.0001).
• In vitro verapamil exposure did not affect fibrinogen binding, but prolonged in vivo exposure reduced receptor expression and intracellular calcium release.

Conclusions:

• Prolonged in vivo verapamil administration, unlike short-term in vitro exposure, reduces platelet fibrinogen receptor expression.
• Verapamil's anti-platelet effect is mediated by altered intraplatelet signaling, specifically reduced calcium release, not solely receptor number reduction.
• These findings suggest verapamil may modulate thrombosis risk through effects on platelet function beyond its known cardiovascular actions.