The effect of 5‐hydroxytryptamine on the potassium exchange of human platelets

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Abstract
1. The concentration of potassium in platelets freshly isolated from nine persons was 74 ± 4·8 μmole/1011 platelets (mean ± S.E.M.).2. The influx of potassium into platelets from citrated plasma at 37° C, estimated with the use of 42K, was 18·3 ± 1·6 n‐mole/sec. 1011 platelets.3. When plasma contained 5‐hydroxytryptamine (5‐HT) at a concentration of about 5 μg/ml., the influx of potassium into platelets was increased for as long as they took up 5‐HT. This effect was absent when the concentration of 5‐HT was either lower (2 μg/ml.) or much higher (50 μg/ml.).4. The concentration of 5‐HT in the platelets did not affect their potassium flux.