Cellular activity of dopamine DA2 receptor splice variants and mutants.

Two splice variants of the dopamine D2 (DA2) receptors-a long (DA2l) and short (DA2s) form-and two corresponding mutants (serine at position 311 replaced by a cysteine) have been described. Using CHO-cells transfected with the genes for the splice variants and their respective mutants and a bioassay based on the online registration of the extracellular acidification rate (ECAR) of intact cells, we investigated the cellular activity upon stimulation of the receptor. We first confirmed that the acute response upon short agonist stimulation was significantly higher for DA2s than for DA2l. However, in contrast to the ongoing opinion, we found that the desensitisation pattern upon long-term agonist treatment was indistinguishable for both wild-type receptors. As far as the corresponding ser311cys mutated receptors are concerned, the concentration-response curves and the desensitisation pattern were superimposable to the corresponding wild-type receptors. Inhibition of protein kinase C (PKC) had very little effect both on the concentration-response curves and on the desensitisation pattern. We conclude that signal transduction following stimulation of DA2 receptors in the CHO expression system is more effective for DA2s than for DA2l. The point mutation in position 311 has little impact on the downstream signalling of DA2 receptors.