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Transient calcium elevation in polymorphonuclear leukocytes triggered by thrombin-activated platelets
A Takahashi1, K Yamamoto, M Okuma
1Department of Internal Medicine, Faculty of Medicine, Kyoto University, Japan.
Abstract:
The effect of thrombin-activated platelets and their release products on the intracellular free calcium concentration ([Ca2+]i) of human polymorphonuclear leukocytes (PMNs) was studied by loading PMNs with a fluorescent indicator of calcium, fura-2. [Ca2+]i of PMNs was transiently elevated by thrombin-activated platelets. The supernatant of thrombin-activated platelets also elicited a transient elevation of [Ca2+]i in PMNs. Pretreatment of the supernatant with hexokinase caused a decrease in the transient [Ca2+]i elevation of PMNs, while hexokinase abrogated the [Ca2+]i elevation of PMNs elicited by 80 mumol/l adenosine triphosphate (ATP). Pretreatment of the supernatant with trypsin also decreased the magnitude of the elevation, while trypsin had no effect on the response to ATP. These findings suggest that thrombin-activated platelets induce a transient [Ca2+]i elevation in PMNs by releasing ATP and some trypsin-sensitive factor(s).
Insights
Thrombin-activated platelets release adenosine triphosphate (ATP) and other factors that transiently increase intracellular calcium in human polymorphonuclear leukocytes (PMNs). This calcium signaling is crucial for PMN function.
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Platelets play a critical role in hemostasis and immune responses.
- Polymorphonuclear leukocytes (PMNs) are key immune cells involved in inflammation and host defense.
- Calcium signaling is fundamental to cellular activation and function in both platelets and PMNs.
Purpose of the Study:
- To investigate the effect of thrombin-activated platelets and their secreted products on intracellular calcium levels in human PMNs.
- To identify the specific factors released by activated platelets that modulate PMN calcium concentration.
Main Methods:
- Human PMNs were loaded with the calcium indicator fura-2.
- The intracellular free calcium concentration ([Ca2+]i) was measured using fluorescence.
- Supernatants from thrombin-activated platelets were applied to PMNs.
- The effects of hexokinase and trypsin pretreatment on PMN [Ca2+]i responses were assessed.
Main Results:
- Thrombin-activated platelets and their supernatant caused a transient increase in PMN [Ca2+]i.
- Hexokinase pretreatment reduced the [Ca2+]i elevation, while it abrogated the response to adenosine triphosphate (ATP).
- Trypsin pretreatment decreased the magnitude of the [Ca2+]i elevation, but did not affect the ATP-induced response.
Conclusions:
- Thrombin-activated platelets release ATP, which contributes to the transient elevation of [Ca2+]i in PMNs.
- Activated platelets also release a trypsin-sensitive factor that influences PMN intracellular calcium.
- These findings elucidate a mechanism of platelet-leukocyte communication involving calcium signaling.