Heterogeneous signal pathways through TSH receptors in porcine thyroid cells following stimulation with Graves' immunoglobulin G.

Objective: We compared different signal transduction pathways through thyroid stimulating hormone receptor (TSH-R) in porcine thyroid cells (PTC) following stimulation with thyroid stimulating hormone (TSH) and 11 thyroid stimulating immunoglobulin samples (TSI) obtained from patients with Graves' disease.

Design: Following stimulation with TSI, the level of inositol trisphosphate (IP3) and [Ca2+]i, as well as the membrane bound protein kinase C (PKC) activity and the intensity of the arachidonic acid (AA) cascade, were determined in PTC.

Results: Seven out of eleven TSI samples activated PTC through IP3 generation, elevated [Ca2+]i from the intracellular pools, exhibited verapamil-insensitive membrane-bound PKC activation, and enhanced release of [14C]AA derivates (however, one of the samples was also able to take up Ca2+ from the extracellular space). Four out of eleven TSI samples did not activate the phospholipase C (PLC) system in which case the Ca2+ signal occurred only in the presence of extracellular Ca2+, the membrane bound PKC activation was verapamil sensitive, and in two of these four TSI samples, the AA release was extremely high.

Conclusions: The simultaneous examination of the majority of the known signal pathways using TSI samples showed that TSI samples from different patients activate thyroid cells through different pathways. Their effects differ from that of TSH and, to a certain extent, from each other. The results give a certain new insight into the intracellular mechanisms exerted by TSI.