Abstract
The calcium responses to serotonin and thrombin, as assessed using the fluorescent indicator Fura-2, have been investigated in platelets taken from 59 non-smokers and 17 smokers. The peak responses above baseline, calculated either as fluorescence ratios or calibrated calcium concentrations, were in the order of magnitude thrombin 520 mU/ml>thrombin 52 mU/ml≫serotonin 1 μmol/l≈serotonin 100 μmol/l. Multiple regression analyses indicated that the responses to 1 μmol/l serotonin, but not the responses to thrombin, were significantly correlated with the serotonin 2A receptor density measured using [ 3H]LSD as radioligand. No effects of age, gender, smoking habit or the time of year of sampling were seen on the calcium responses to serotonin and thrombin. It is concluded that cellular processes distal to the serotonin 2A receptor recognition site may compensate to some extent for the large differences in recognition site expression, thus underlining the importance of providing a functional correlate in addition to [ 3H]LSD binding site densities when studying platelet serotonin 2A receptors in neuropsychiatric disorders. The measurement of Ca 2+ responses to serotonin provides a useful such functional correlate.
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