Oral and integumental uptake of free exogenous glycine by the Japanese spiny lobster Panulirus japonicus phyllosoma larvae

Abstract

SUMMARY The possibility of direct integumental absorption of the amino acid glycine from a solution in seawater was investigated in 250–260 day old (16.9–50.0 mg wet mass) phyllosoma larvae of the Japanese spiny lobster Panulirus japonicus Von Siebold 1824. The uptake of the amino acid was assessed by autoradiography and liquid scintillation counting (LSC) of larvae incubated with [2-3H]glycine and the net uptake was estimated by a time course high-performance liquid chromatography (HPLC) analysis of the concentration of glycine in the incubation medium. Autoradiography revealed the presence of labelled glycine in the cuticle, epidermis and internal tissues (digestive system, muscle, haemocytes) within 30 min of the onset of incubation. Absorption through the integument was confirmed by autoradiography and LSC as glycine uptake was observed even in larvae whose mouths were artificially sealed with cyanoacrylate bond prior to incubation. Scanning electron microscopic examination of the body surface revealed no bacterial population that could have mediated the uptake. HPLC revealed a consistent net uptake (0.29–0.39 μmol g−1 body mass h−1) of glycine in larvae incubated in 6 μmol l−1 glycine and high individual variation (e.g. absorption or release) in larvae incubated at higher concentrations (30 and 60 μmol l−1). Thus, the results of this study provide clear confirmation that, in addition to the known mode of oral feeding on macroscopic food masses, P. japonicus phyllosoma larvae are also able to absorb nutrients directly from the surrounding medium.