Autoradiographic analysis of amino acid uptake by the gill of Mytilus

Autoradiography was used to examine the influence of lateral ciliary activity on the pattern of leucine uptake into isolated gill tissue from the mussel, Mytilus californianus. Metachronal activity of the lateral cilia, normally absent in the in vitro gill, was reestablished by application of 10 μM 5-hydroxytryptamine (5-HT). This treatment produced a 5-7 fold stimulation in the rate of leucine uptake into isolated gills. The treatment with 5-HT did not, however, affect the fractional incorporation of leucine into alcohol insoluble vs alcohol soluble material. Autoradiograms of gills treated with 5-HT showed extensive labelling of frontal, lateral, and abfrontal surfaces of gill filaments compared to the control condition in which label was largely confined to the frontal region of the gill. Quantitative analyses of the autoradiograms revealed a 4-fold increase in the number of silver grains over lateral and abfrontal surfaces compared to control gills. Autoradiograms of gills from intact mussels exposed to³H-leucine showed a pattern of silver grain deposition similar to that observed in in vitro gills treated with 5-HT. It is concluded that the capacity for amino acid transport exists in cells from the frontal, lateral, and abfrontal surfaces of gill filaments, butaccess to dissolved substrates by transport sites on lateral and abfrontal surfaces is dependent upon lateral ciliary activity.