CLONING AND CHARACTERIZATION OF AN OLFACTORY CYCLIC NUCLEOTIDE-GATED CHANNEL EXPRESSED IN MOUSE HEART

Regulation of ionic currents in the heart is partly achieved by signal ing cascades which alter intracellular levels of cyclic nucleotides. C hanges in cyclic nucleotide levels can regulate channels either direct ly, like the direct binding of cAMP to the ii channel in pacemaker tis sues, or indirectly through phosphorylation of channels by cAMP-depend ent, or cGMP-dependent protein kinases. These types of regulation gene rally alter the voltage sensitivities of channels, A class of voltage- insensitive channels, first discovered in retinal rods and olfactory n eurons, were recently identified in the heart. These channels are open ed by the direct binding of cyclic nucleotides, providing a means of r egulating ionic currents outside the influence of membrane voltage. Si nce different isoforms have different affinities for cAMP and cGMP, it is important to determine which isoforms are expressed in heart in or der to predict their roles in heart function. We have cloned the olfac tory channel from mouse heart, and find that although the message is v ery rare, Western blot analysis indicates the olfactory channel protei n is stable in heart sarcolemma. Our data also suggest the olfactory c hannel protein forms homomeric channels in the heart since other isofo rms or splice variants were not detected either by PCR amplification o r by RNase protection. In addition, we have isolated and sequenced the mouse olfactory cyclic nucleotide-gated channel gene, and show the ge nomic organization is remarkably similar to that found in the human re tinal channel gene. Part of this work was presented in abstract form. (C) 1996 Academic Press Limited.