The effect of ouabain on amino acid and orthophosphate influxes in squid giant axons.

Abstract

4. A detailed investigation of the time course of the inhibition of amino acid uptake by ouabain in which intracellular scintillator techniques were used, showed that there was no inhibition for 30-100 min, and then it occurred fairly quickly. This course of events was not affected by the protein synthesis inhibitor cycloheximide. It is unlikely that the inhibition of orthophosphate uptake is subject to a similar delay since this had reached a maximum after 40 min.5. It is concluded that the inhibitory effects of ouabain on amino acid uptake in squid axons are not due to effects on the Na and K gradients brought about by inhibition of the Na-K pump. The delay in the inhibition may reflect the operation of an intracellular regulatory mechanism, which is initiated when ouabain inhibits the pump but which takes time to operate. If the formation of an inhibitory second messenger molecule is involved this is unlikely to be a protein.

Amino acid transport in Myxicola giant axon: stability of the amino acid pool, taurine efflux, and trans effect of sodium

“…The magnitude range is about the same as the apparent Vmax for cysteine influx (Hoskin & Brande, 1973) and for one component of glycine influx (Caldwell & Lea, 1978) in squid. However, the range is at least tenfold larger than glutamate influx or efflux (Baker & Potashner, 1973;Caldwell & Lea, 1979) or glycine efflux (Caldwell & Lea, 1978) in squid. The taurine efflux in Nao-free ASW is about five times smaller than the corresponding net efflux estimated in 2 h soak experiments.…”