title: The internal calcium concentration of human platelets increases during chilling.
abstract: Human platelets must be stored at 22 degreesC in blood banks, because of the well-known phenomenon of cold-induced activation. When human platelets are chilled below room temperature, they undergo shape change and vesicle secretion that resembles physiological agonist-mediated activation. The trigger for the cascade of events leading to platelet activation at hypothermic temperatures is not known, although an increase in the internal calcium concentration ([Ca]i) due to passage of the platelet membranes through their thermotropic phase transition has been proposed. We report here that the fluorescent calcium-sensitive probe, Indo-1, has been used to estimate the internal calcium concentration of human platelets during a reduction in temperature from 20 degreesC to 5 degreesC at a rate of 0.5 degreesC/min. An increase on the order of 100 nM was recorded. Almost all of the increase in [Ca2+]i occurs during the chilling process, as incubation of platelets for 1 h at low temperature did not lead to a continued calcium concentration increase. The increase in [Ca2+]i during chilling is likely to be due to more than a single mechanism, but might include some release of the calcium stores from the dense tubule system. Loading platelets with the calcium chelator BAPTA (1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) dramatically reduced the increase in [Ca2+]i seen during chilling. Antifreeze glycoproteins (AFGPs) isolated from the blood serum of Antarctic fishes, which are known to protect platelets from cold-induced activation, did not eliminate the rise in [Ca2+]i during chilling, suggesting that signaling mechanisms are likely to be involved in cold-induced activation.
authors.affiliation: Section of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA. aeoliver@ucdavis.edu
authors.forename: A E
authors.initials: AE
authors.lastname: Oliver
authors.forename: F
authors.initials: F
authors.lastname: Tablin
authors.forename: N J
authors.initials: NJ
authors.lastname: Walker
authors.forename: J H
authors.initials: JH
authors.lastname: Crowe
mesh_terms: D021301:Antifreeze Proteins; D001771:Blood Banks; D001792:Blood Platelets / Q000737:chemistry*; D002118:Calcium / Q000032:analysis*; D002463:Cell Membrane Permeability; D003080:Cold Temperature; D006023:Glycoproteins / Q000737:chemistry; D006801:Humans; D007211:Indoles; D015539:Platelet Activation; D013917:Thrombin / Q000737:chemistry
chemical_list: D021301:Antifreeze Proteins; D006023:Glycoproteins; D007211:Indoles; D013917:Thrombin; C048960:indo-1; D002118:Calcium