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'Funny' current: if heart rate slowing is not the best answer, what might be?
| Content Provider | Semantic Scholar |
|---|---|
| Author | Gewirtz, Henry |
| Copyright Year | 2009 |
| Abstract | DiFrancesco first described an ion current in the sinoatrial node (SAN) of the rabbit which was thought 'funny', as is unusual, since it was hyperpolarization-activated and carried by both sodium and potassium ions.1,2 Hence, its name I f. The current is active in diastole between roughly −50 and −20 mV when it shuts down and is followed by the activation of the T-channel calcium current, which continues the process of diastolic depolarization. Accordingly, I f contributes significantly to spontaneous pacemaker activity in the mammalian heart.1 The gene encoding the channel was first discovered in the mouse brain.3 Subsequently, in the cardiac tissue, four isoforms of the hyperpolarization-activated, cyclic nucleotide-gating channel protein (HCN 1,2,3,4) were identified.1,4 The channel's operating range and activity are sensitive to cAMP (second messenger role) and so autonomic tone, both sympathetic and parasympathetic.1 The distribution of isoforms in the rabbit heart also is variable, with HCN4 greater than HCN1 in SAN, whereas much lower levels of HCN2 are found in ventricular myocardium,5 but given the very large mass of myocytes vs. SAN tissue, HCN2 likely is the dominant isoform on a mass basis.5 Finally, the I f current is active at a threshold of −45 mV in the rabbit SAN but is only faint at hyperpolarization to −150 mV in rabbit myocytes.5 However, it is readily apparent at −100 mV in … *Corresponding author. Tel: +1 617 724 3650; fax: +1 617 724 3636/3600. E-mail address : hgewirtz{at}partners.org; gewirtz.henry{at}mgh.harvard.edu |
| Starting Page | 9 |
| Ending Page | 10 |
| Page Count | 2 |
| File Format | PDF HTM / HTML |
| DOI | 10.1093/cvr/cvp245 |
| PubMed reference number | 19617225 |
| Journal | Medline |
| Volume Number | 84 |
| Issue Number | 1 |
| Alternate Webpage(s) | http://cardiovascres.oxfordjournals.org/content/cardiovascres/early/2009/07/17/cvr.cvp245.full.pdf |
| Alternate Webpage(s) | https://doi.org/10.1093/cvr%2Fcvp245 |
| Journal | Cardiovascular research |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
