INHIBITION OF FUNCTION IN XENOPUS OOCYTES OF THE INWARDLY RECTIFYING G-PROTEIN-ACTIVATED ATRIAL K-CHANNEL (GIRK1) BY OVEREXPRESSION OF A MEMBRANE-ATTACHED FORM OF THE C-TERMINAL TAIL

Coexpression in Xenopus oocytes of the inwardly rectifying guanine nucleotide binding (G)-protein-gated K channel GIRK1 with a myristoylated modification of the (putative) cytosolic C-terminal tail [GIRR1 aa 183-501 fused in-frame to aa 1-15 of p60(src) and denoted src(+)(183-501)] leads to a high degree of inhibition of the inward G-protein-gated K+ current. The nonmyristoylated segment, src(-)(183-501), is not active, Although some interference with assembly is not precluded, the evidence indicates that the main mechanism of inhibition is interference with functional activation of the channel by G proteins, In part, the tail functions as a blocking particle similar to a ''Shaker ball''; it may also function by competing for the available supply of free G beta gamma liberated by hormone activation of a seven-helix receptor, The non-G-protein-gated weak inward rectifier ROMK1 is less effectively inhibited, and a Shaker K channel was not inhibited. Immunological assays show the presence of a high concentration of src(+)(183-501) in the plasma membrane and the absence of any membrane forms for the nonmyristoylated segment.