Changes in Free Calcium Concentrations in Platelets of SHRSP and WKY: Its Relationship to ATP Releasing Potencies and Platelet Aggregation Activities Upon Stimulation of Several Reagents

Abstract

To clarify the relationships between free calcium levels, ATP release and aggregation potencies of SHRSP platelets, we examined the platelets from 9-month-old SHRSP and WKY using fura-2AM and luciferine-luciferase. In the absence of extracellular Ca²⁺, each reagent elevated the free calcium level to the same extent in the samples of both SHRSP and WKY. With regard to ATP release, thrombin and collagen less potentiated the platelet action in SHRSP than WKY, and ATP release was not affected by extracellular Ca²⁺. Collagen and ADP induced aggregations showed lower activities in SHRSP than WKY. TPA caused higher Ca²⁺ influx and aggregation activity in SHRSP than WKY in the presence of extracellular Ca²⁺. These results indicate that Ca²⁺ release must be followed by ATP release, and ATP release may be less potentiated, while thrombin and TPA induced aggregation is likely to be stimulated in SHRSP platelets, because protein kinase C activity in SHRSP platelets appears to be high.

Key Words:

• SHRSP
• platelet
• free calcium
• ATP release
• aggregation