Influence of Temperature on the Amplitude of Platelet [Ca2+]i Transients
| Agonist . | Agonist-Induced Peak Increment in Platelet [Ca2+]i (nmol/L) . | |||
|---|---|---|---|---|
| 20°C . | 25°C . | 30°C . | 37°C . | |
| vWF* (5 μg/mL) | 1† (1 to 5) | 1† (−2 to 1) | 9† (−1 to 21) | 61 (40 to 83) |
| U-46619 (0.1 μmol/L) | 178 (164 to 192) | 167 (160 to 193) | 157 (134 to 169) | 143 (129 to 179) |
| α-Thrombin (0.02 U/mL) | 165†,‡,1-153 (139 to 207) | 103†,‡ (64 to 167) | 75† (44 to 112) | 52 (33 to 62) |
| ADP (5 μmol/L) | 141† (126 to 159) | 155† (142 to 179) | 138† (107 to 145) | 101 (97 to 131) |
| Arachidonic acid (20 μmol/L) | 0†,‡ (0 to 1) | 0†,‡ (0 to 1) | 4† (3 to 7) | 49 (24 to 51) |
| Resting platelet [Ca2+]i | 7†,‡,1-153 (6 to 9) | 9†,‡ (7 to 10) | 11† (10 to 13) | 13 (11 to 15) |
| Agonist . | Agonist-Induced Peak Increment in Platelet [Ca2+]i (nmol/L) . | |||
|---|---|---|---|---|
| 20°C . | 25°C . | 30°C . | 37°C . | |
| vWF* (5 μg/mL) | 1† (1 to 5) | 1† (−2 to 1) | 9† (−1 to 21) | 61 (40 to 83) |
| U-46619 (0.1 μmol/L) | 178 (164 to 192) | 167 (160 to 193) | 157 (134 to 169) | 143 (129 to 179) |
| α-Thrombin (0.02 U/mL) | 165†,‡,1-153 (139 to 207) | 103†,‡ (64 to 167) | 75† (44 to 112) | 52 (33 to 62) |
| ADP (5 μmol/L) | 141† (126 to 159) | 155† (142 to 179) | 138† (107 to 145) | 101 (97 to 131) |
| Arachidonic acid (20 μmol/L) | 0†,‡ (0 to 1) | 0†,‡ (0 to 1) | 4† (3 to 7) | 49 (24 to 51) |
| Resting platelet [Ca2+]i | 7†,‡,1-153 (6 to 9) | 9†,‡ (7 to 10) | 11† (10 to 13) | 13 (11 to 15) |
Platelet [Ca2+]i was monitored with Fura-PE3 using an aggregometer cuvette and the novel stirrer. Parallel studies were performed at four temperatures (20°C to 37°C); all measurements were conducted in the presence of extracellular calcium (1 mmol/L CaCl2). The various agonists were used at concentrations that gave [Ca2+]i transients of similar amplitude at 37°C. Peak increments in platelet [Ca2+]i were calculated from the difference between an agonist-stimulated sample and the corresponding control; in the absence of a perceptible [Ca2+]itransient (vWF and arachidonic acid stimulation at the lower temperatures), this difference was determined at the time of the peak for the transient at 37°C. Data are presented as the median value from eight studies with vWF, seven studies with arachidonic acid, and six studies with each of the other agonists; the interquartile range is shown in parentheses. Data on resting platelet [Ca2+]i (based on average values before addition of each agonist) are also included.
Stimulation was with 5 μg/mL multimeric human vWF in the presence of 1 mg/mL ristocetin.
Statistical analysis used Friedman’s test with a nonparametric Student-Newman-Keuls posthoc test; significant differences (P < .05) from measurements at the higher temperatures are designated:
compared with 37°C;
compared with 30°C; and
compared with 25°C.