Functional characterization of Ih-channel splice variants from Apis mellifera

We isolated splice variants of the AMIH cDNA by means of polymerase chain reaction and homology screening. Splicing at one site generates at least four different channel transcripts (AMIH, AMIH(L), AMIH(M) and AMIH(T)), which code for ion-channel proteins that vary in the interloop regions between the membrane-spanning domains S4 and S5. HEK293 cells in which the AMIHL splice variants were functionally expressed generated currents that were activated by hyperpolarizing voltage steps. Compared to AMIH, AMIHL cells showed pronounced differences in the voltage dependency of activation: the incorporation of 32 extra amino acids between S4 and S5 shifts the activation curve by +25 mV. Intracellular cAMP made the current-activation potential still less negative and accelerated the activation more effectively than it does in AMIH cells. In vertebrates, functional diversity Of I-h-channels is generated by four different genes. In Apis mellifera, splice variants coded by the single gene AMIH could generate a similar diversity. (C) 2004 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.