Functional expression and cellular mRNA localization of a G protein-activated K+ inward rectifier isolated from rat brain.

We have cloned by homology screening from a rat brain cDNA library a GIRK3-type (Kir 3.3) inwardly rectifying K+ channel subunit with high structural similarity to other subfamily members whose activity is thought to be controlled by receptor-stimulated G proteins. When heterologously expressed both in Xenopus oocytes and in mammalian COS-7 cells, rbGIRK3 subunits individually fail to form functional channels.

IRK(1-3) and GIRK(1-4) inwardly rectifying K+ channel mRNAs are differentially expressed in the adult rat brain.

Molecular cloning together with functional characterization has shown that the newly identified family of inwardly rectifying K+ channels consists of several closely related members encoded by separate genes. In this report we demonstrate the differential mRNA expression and detailed cellular localization in the adult rat brain of seven members of the IRK and GIRK subfamilies. Using both radiolabeled cRNA riboprobes and specific oligonucleotide probes directed to nonconserved regions of both known and newly isolated rat brain cDNAs, in situ hybridization revealed wide distribution with partly overlapping expression of the mRNAs of IRK1-3 and GIRK1-4.

A G-protein-activated inwardly rectifying K+ channel (GIRK4) from human hippocampus associates with other GIRK channels.

Transcripts of a gene, GIRK4, that encodes for a 419-amino-acid protein and shows high structural similarity to other subfamily members of G-protein-activated inwardly rectifying K+ channels (GIRK) have been identified in the human hippocampus. When expressed in Xenopus oocytes, GIRK4 yielded functional GIRK channels with activity that was enhanced by the stimulation of coexpressed serotonin 1A receptors. GIRK4 potentiated basal and agonist-induced currents mediated by other GIRK channels, possibly because of channel heteromerization.

Immunocytochemical localization of gelsolin in fibroblasts, myogenic cells, and isolated myofibrils.

Gelsolin was localized by immunofluorescence in fibroblasts and skeletal muscle cells using antibodies which eliminated the risk of detecting xenogenic plasma gelsolin. Gelsolin was consistently found to be closely associated with the elements of the microfilament system: In fibroblasts, a preferential labeling of the stress fibers was observed, whereas with myogenic cells and myofibrils isolated from skeletal muscle, a specific staining of the I-Z-I region in the sarcomeres was found. From double labeling of gelsolin and actin it became evident that the staining patterns for both proteins were practically coincident: The width and location of the fluorescent bands varied with the degree of contraction of the myofibrils.