Carbamylcholine, TRH, PGF2 alpha and fluoride enhance free intracellular Ca++ and Ca++ translocation in dog thyroid cells

Effects on Ca++ translocation and [Ca++]i were studied in dog thyroïd cell monolayers using both 45Ca++ efflux and the indicator quin-2. Carbamylcholine, a non hydrolysable analog of acetylcholine, through muscarinic receptors, and to a lesser extent TRH and PGF2 alpha increased both these parameters. [Ca++]i increased by 171, 100 and 75% respectively over a basal level of 66 +/- 17 nM (mean +/- SD). The response to carbamylcholine was biphasic. A transient increase in [Ca++]i was followed by a more sustained phase where the [Ca++]i was slightly higher than the basal level. Only the first phase was insensitive to extracellular Ca++ depletion. This phase is probably due to a release of Ca++ from an intracellular store. NaF also induced a sustained rise in [Ca++]i dependent on extracellular Ca++ and affected 45Ca++ efflux. Our data provide direct evidence of an implication of intracellular Ca++ in the response of dog thyroïd cells to all these agents.