Carbamylcholine and thyrotropin activate distinctive pathways of protein phosphorylation in dog thyroid

The role of protein phosphorylation in the regulation of thyroid function by carbamylcholine was investigated using dog thyroid slices incubated in the presence of [32P]phosphate and two-dimensional electrophoresis. In these intact cells, carbachol increased the phosphorylation of three polypeptides with Mr values of 21500, 24 000 and 29000. Maximal [32P]phosphate incorporation occurred within 5 min of addition of carbamylcholine and was still observed after 10 min of action of this agent. Incubation of dog thyroid slices with thyrotropin for 10 min increased the phosphorylation of 11 polypeptides which were identical to those observed previously after 2 h of hormone action (Lecocq, R., Lamy, F. and Dumont, J.E. (1979) Eur. J. Biochem. 102, 147-152). All three polypeptides whose phosphorylation is increased by carbamylcholine were different from those whose phosphorylation is increased by thyrotropin. Under our experimental conditions, the calcium ionophore A23187 did not stimulate significantly [32P]phosphate incorporation in these three polypeptides. In conclusion, our results show that carbamylcholine and thyrotropin, which have some antagonist and some similar effects on dog thyroid, do not act through the phosphorylation of the same proteins. Although we have, in our previous paper, established that a rise in intracellular cyclic AMP could account for the effect of thyrotropin on protein phosphorylation, the nature of the intracellular mediator of carbamylcholine action on this parameter is still uncertain.