| First Author | Rozario AO | Year | 2009 |
| Journal | Biochim Biophys Acta | Volume | 1788 |
| Issue | 9 | Pages | 1939-49 |
| PubMed ID | 19524546 | Mgi Jnum | J:153459 |
| Mgi Id | MGI:4365498 | Doi | 10.1016/j.bbamem.2009.06.003 |
| Citation | Rozario AO, et al. (2009) Voltage-dependent opening of HCN channels: Facilitation or inhibition by the phytoestrogen, genistein, is determined by the activation status of the cyclic nucleotide gating ring. Biochim Biophys Acta 1788(9):1939-49 |
| abstractText | Investigation of the mechanistic bases and physiological importance of cAMP regulation of HCN channels has exploited an arginine to glutamate mutation in the nucleotide-binding fold, an approach critically dependent on the mutation selectively lowering the channel's nucleotide affinity. In apparent conflict with this, in intact Xenopus oocytes, HCN and HCN-RE channels exhibit qualitatively and quantitatively distinct responses to the tyrosine kinase inhibitor, genistein -- the estrogenic isoflavonoid strongly depolarizes the activation mid-point of HCN1-R538E, but not HCN1 channels (+9.8 mV + or - 0.9 versus +2.2 mV + or - 0.6) and hyperpolarizes gating of HCN2 (-4.8 mV + or - 1.0) but depolarizes gating of HCN2-R591E (+13.2 mV + or - 2.1). However, excised patch recording, X-ray crystallography and modeling reveal that this is not due to either a fundamental effect of the mutation on channel gating per se or of genistein acting as a mutation-sensitive partial agonist at the cAMP site. Rather, we find that genistein equivalently moves both HCN and HCN-RE channels closer to the open state (rendering the channels inherently easier to open but at a cost of decreasing the coupling energy of cAMP) and that the anomaly reflects a balance of these energetic effects with the isoform-specific inhibition of activation by the nucleotide gating ring and relief of this by endogenous cAMP. These findings have specific implications with regard to findings based on HCN-RE channels and kinase antagonists and general implications with respect to interpretation of drug effects in mutant channel backgrounds. |
