Regulation of cytosolic calcium by collagen in single human platelets

Open Access
Publisher Website
Google Scholar
Abstract
There is controversy in the literature as to whether collagen is able to induce directly a rise in cytosolic calcium concentration ([Ca2+]i) in human platelets. We have addressed this question by observing the cytosolic calcium response of single fura‐2‐loaded human platelets settling onto a collagen‐coated surface using dynamic fluorescence ratio imaging. Following a short lag phase after adherence to collagen fibres, platelets underwent a rapid rise in cytosolic calcium from basal values of 80 ± 13 nM (n = 24) to a peak of 475 ± 42 nM (n = 24) which was sustained for the remaining period of the experiment. The tyrphostin protein tyrosine kinase inhibitor, ST271, reduced substantially the proportion of platelets which exhibited a rise in [Ca2+]i on adherence to collagen and transformed the response in remaining cells to one of oscillations. In contrast, and as a control for collagen, laminin‐coated surfaces induced adherence of human platelets without elevating intracellular [Ca2+]; the cells however remained responsive to ADP. We conclude that collagen directly induces a rise in cytosolic calcium in single human platelets through a tyrosine kinase‐mediated pathway.