Intracellular receptors are receptors located inside the cell rather than on its cell membrane . Classic hormones that use intracellular receptors include thyroid and steroid hormones. Examples are the class of nuclear receptors located in the cell nucleus and cytoplasm and the IP 3 receptor located on the endoplasmic reticulum . The ligands that bind to them are usually intracellular second messengers like inositol trisphosphate (IP 3 ) and extracellular lipophilic hormones like steroid hormones . Some intracrine peptide hormones also have intracellular receptors.
two muscarinic receptors subtypes (machrs), m2 and m3, have been reported to regulate in opposite ways the activity of a membrane-bound guanylyl cyclase (gcm) via g-proteins in bovine tracheal smooth muscle (btsm). the present study was undertaken to identify the primary sequences from intracellular loops of machrs subtypes from btsm involved in the interaction with these g-proteins. cdna from btsm was used to amplify via rt-pcr, by using specific primers, the intracellular regions of m2 and m3 involved in the interaction with g-proteins. amplification products for m3 and m2 loops were readily identified in agarose gel electrophoresis. sequences for these loops were almost identical (99%) those found in bovine brain m2 and m3 machrs. this is the first molecular cloning of m2 and m3 machrs for btsm. these results suggest the existence of similar machrs/g-proteins interactions in bovine airways.