Insulin secretion is stimulated by glucose, hormones and neurotransmitters. Both activation of a non-selective cation current and activation of a Ca^{2 +} current in response to depletion of intracellular Ca^{2 +} stores have been suggested to play a role in this stimulation. The properties of these currents resemble those reported for the Drosophila genes trp and trpl. Using the reverse transcription polymerase chain reaction and Northern blot analysis we found that of the six mammalian trp-related genes (trp1–6), only trp1 was expressed at high levels in the mouse insulinoma cell line MIN6. We cloned the murine homologue of human trp1 from MIN6 cells and identified four variants (α, β, γ and δ), generated by alternative splicing near the N-terminus of the protein. In vitro translation showed that only the α and β splice variants are efficiently expressed. The β variant is the dominant form in MIN6 cells (and probably in mouse pancreatic islets), whereas the α variant is the major type in the mouse brain. The β variant showed 99 % identity to the human homologue at the amino acid level. [Diabetologia (1997) 40: 528–532]