Cloning and characterization of Kir3.1 (GIRK1) C-terminal alternative splice variants

Southern blot analysis of RT-PCR products from brain and heart revealed multiple products for a C-terminal region of Kir3.1. Sequencing yielded clones for wild-type Kir3.1 and three Kir3.1 C-terminal alternative splice variants, including a unique alternative exon. Two of these variants encoded truncated Kir3.1 molecules. Tissue distribution and electrophysiological characterization of a single truncated variant, Kir3.1₀₀ were then examined. Kir3.1 channels are gated by G-protein βγ-subunits binding to the C-terminal domain, thus, the truncation of Kir3.1₀₀ removes a major functional domain. When incorporated into heteromeric channels with other family members (Kir3.1, 3.2 or 3.4) several functional changes were observed: (1) Kir3.1₀₀ changes G-protein activation of Kir3 channels; (2) Kir3.1₀₀ is restricted in its ability to assemble with other channel subunits as heteromers; and (3) incorporation of Kir3.1₀₀ into heteromeric channel complexes alters the kinetics of channel re-activation.