RECONSTITUTION AND CHARACTERIZATION OF 2 FORMS OF CYCLIC NUCLEOTIDE-GATED CHANNELS FROM SKELETAL-MUSCLE

A cyclic nucleotidegated channel present in skeletal muscle plasma mem brane has previously been identified as being responsible for insulin- activated sodium entry into muscle cells (J. E. M. McGeoch and G. Guid otti. J. Biol. Chem. 267: 832-841, 1992). We have isolated this channe l activity to further study and characterize it. The channel was solub ilized from rabbit skeletal muscle sarcolemma and functionally reconst ituted into phospholipid vesicles, as assayed by patch-clamp analysis of the reconstituted proteins. Channel activity was isolated by 8-brom o-guanosine 3',5'-cyclic monophosphate affinity chromatography, produc ing two distinct peaks of cyclic nucleotidegated channel activity. The se two types of channel activity differ in guanosine 3',5'-cyclic mono phosphate affinity and in the ability to be opened by adenosine 3',5'- cyclic monophosphate. The cyclic nucleotide-gated channel from rod out er segments also forms two peaks of activity when purified in this man ner. The presence of two forms of channel activity could have implicat ions for the mechanism of insulin-activated sodium entry.