Sodium-dependent transport of 5-hydroxytryptamine (serotonin) by canine blood platelets |
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Authors: | Garyen Chong William W. Kay |
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Affiliation: | Departments of Biochemistry and Surgery, University of Saskatchewan, Saskatoon, Saskatchewan, Canada |
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Abstract: | The transport of 5-hydroxytryptamine (5-HT) was shown to be strongly dependent on the presence of Na+ in the incubation medium whereas divalent cations were without effect. The Km for the Na+ requirement was 16.8 mm. The addition of Na+ to Na+-depleted platelets restored maximum 5-HT transport within 3 min. The affinity of the 5-HT carrier for its substrate was directly proportional to the concentration of Na+; however, below 25 mm Na+ unique reversible morphological changes in platelet shape occurred as revealed by scanning electron microscopy which resulted in a drastically reduced affinity for 5-HT. K+, choline (Ch+), or Li+ could be used as counterbalancing cations to maintain osmolarity, and the affinity for 5-HT was also dependent on the concentrations of these ions. Ouabain as well as various ionophores at low concentrations inhibited 5-HT uptake. The inhibition was the result of the destruction of the gradient across the cytoplasmic membrane. Ionophores, however, did not cause the depletion of either intracellular ATP or 5-HT. |
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Keywords: | To whom reprint requests should be sent: Department of Bacteriology and Biochemistry University of Victoria Victoria B.C. Canada V8W 2Y2. |
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