Expression and distribution of voltage-gated ion channels in ferret sinoatrial node

Abstract

Brahmajothi MV, Morales MJ, Campbell DL, Steenbergen C, Strauss HC. Expression and distribution of voltage-gated ion channels in ferret sinoatrial node. Physiol Genomics 42A: 131-140, 2010. First published August 3, 2010 doi:10.1152/physiolgenomics.00049.2010.-Spontaneous diastolic depolarization in the sinoatrial (SA) node enables it to serve as pacemaker of the heart. The variable cell morphology within the SA node predicts that ion channel expression would be heterogeneous and different from that in the atrium. To evaluate ion channel heterogeneity within the SA node, we used fluorescent in situ hybridization to examine ion channel expression in the ferret SA node region and atrial appendage. SA nodal cells were distinguished from surrounding cardiac myocytes by expression of the slow (SA node) and cardiac (surrounding tissue) forms of troponin I. Nerve cells in the sections were identified by detection of GAP-43 and cytoskeletal middle neurofilament. Transcript expression was characterized for the 4 hyperpolarization-activated cation channels, 6 voltage-gated Na ϩ channels, 3 voltage-gated Ca 2ϩ channels, 24 voltagegated K ϩ channel ␣-subunits, and 3 ancillary subunits. To ensure that transcript expression was representative of protein expression, immunofluorescence was used to verify localization patterns of voltagedependent K ϩ channels. Colocalizations were performed to observe any preferential patterns. Some overlapping and nonoverlapping binding patterns were observed. Measurement of different cation channel transcripts showed heterogeneous expression with many different patterns of expression, attesting to the complexity of electrical activity in the SA node. This study provides insight into the possible role ion channel heterogeneity plays in SA node pacemaker activity. gene expression; sodium channels; potassium channels; voltage-gated calcium channels; L-type calcium channels; T-type calcium channels; cyclic nucleotide gated cation channels PRIMARY PACEMAKER CELLS in the central region of the sinoatrial (SA) node undergo spontaneous diastolic depolarization, which ultimately triggers the action potential (AP) upstroke. The excitatory AP wave front subsequently spreads through adjacent areas of the perinodal region to the crista terminalis and atrium. Repolarization of the pacemaker cells allows the cycle to repeat. This inherent cyclic behavior enables the SA node to serve as the normal pacemaker of the heart (7,12,14,26,57).In the central nodal and adjacent perinodal cells, the ionic basis of spontaneous diastolic depolarization and different phases of the AP have been attributed to many currents (7,8,14,27,36,37,42,47,61,68,77). Studies conducted on different mammalian species identified a hyperpolarizationactivated nonselective cation current (I f ), two calcium currents [I Ca,L (L-type) and I Ca,T (T-type)], a sodium current (I Na ), and at least four voltage-dependent potassium currents [ultrarapid (I Kur ), rapid (I Kr ), and slow (I Ks ) delayed rectifier currents and transient outward curre...

Conotoxin κM-RIIIJ, a tool targeting asymmetric heteromeric K v 1 channels

“…The results presented in this study corroborate our previous findings in that the higher-affinity targets of κM-RIIIJ are composed of subunits not abundantly found in cardiomyocytes [for overview, see Nerbonne and Kass (12)]. Curiously, K v 1.1, K v 1.2, and K v 1.6 have been immunodetected in sinoatrial node cells in ferret hearts (13).…”

Augmentation of myocardial If dysregulates calcium homeostasis and causes adverse cardiac remodeling

“…To study the myocardial effect of increased I f under conditions that minimized its influence on heart rate, we have generated transgenic mice that express human HCN4 (HCN4 tg/wt ) under control of the murine cTNI promoter. While abundantly expressed in the working myocardium, cTNI is downregulated in the SAN and the conduction system 22 . This is phenotypically reflected by telemetric recordings revealing similar heart rates and conduction parameters in transgenic and wild type mice (Supplementary Fig.…”

Bi-directional flow of the funny current (If) during the pacemaking cycle in murine sinoatrial node myocytes

“…2E, F). 30 µM TTX was included in our pre-block cocktails because ivabradine has previously been shown to block Na + currents (26) and 30 µM TTX inhibits both weakly TTX-sensitive Nav1.5 channels as well as highly TTX-sensitive Nav1.1 channels expressed in the murine sinoatrial node (42, 43). We found that the Na + -Ca 2+ -K + (NCK) channel blocker cocktail blocked ∼10% of the inward current that was activated during 1 s hyperpolarizations to -120 mV (Fig.…”