Characterization of Multiple Ion Channels in Cultured Human Cardiac Fibroblasts

Abstract

BackgroundAlthough fibroblast-to-myocyte electrical coupling is experimentally suggested, electrophysiology of cardiac fibroblasts is not as well established as contractile cardiac myocytes. The present study was therefore designed to characterize ion channels in cultured human cardiac fibroblasts.Methods and FindingsA whole-cell patch voltage clamp technique and RT-PCR were employed to determine ion channels expression and their molecular identities. We found that multiple ion channels were heterogeneously expressed in human cardiac fibroblasts. These include a big conductance Ca2+-activated K+ current (BKCa) in most (88%) human cardiac fibroblasts, a delayed rectifier K+ current (IKDR) and a transient outward K+ current (Ito) in a small population (15 and 14%, respectively) of cells, an inwardly-rectifying K+ current (IKir) in 24% of cells, and a chloride current (ICl) in 7% of cells under isotonic conditions. In addition, two types of voltage-gated Na+ currents (INa) with distinct properties were present in most (61%) human cardiac fibroblasts. One was a slowly inactivated current with a persistent component, sensitive to tetrodotoxin (TTX) inhibition (INa.TTX, IC50 = 7.8 nM), the other was a rapidly inactivated current, relatively resistant to TTX (INa.TTXR, IC50 = 1.8 µM). RT-PCR revealed the molecular identities (mRNAs) of these ion channels in human cardiac fibroblasts, including KCa.1.1 (responsible for BKCa), Kv1.5, Kv1.6 (responsible for IKDR), Kv4.2, Kv4.3 (responsible for Ito), Kir2.1, Kir2.3 (for IKir), Clnc3 (for ICl), NaV1.2, NaV1.3, NaV1.6, NaV1.7 (for INa.TTX), and NaV1.5 (for INa.TTXR).ConclusionsThese results provide the first information that multiple ion channels are present in cultured human cardiac fibroblasts, and suggest the potential contribution of these ion channels to fibroblast-myocytes electrical coupling.

Prolongation of Action Potential Duration and QT Interval During Epilepsy Linked to Increased Contribution of Neuronal Sodium Channels to Cardiac Late Na + Current

“…The plateau observed at the lower concentration of TTX in the dose-response curve ( Figure 5B) dropped from 76±3% to 65±4% indicating an 11% increase in ƒ TTXs during epilepsy. The increase in the fraction of I Na blocked by low concentration of TTX in epileptic animals is consistent with an augmentation of TTX-sensitive channels (IC 50 ≈ 2-5 nmol/L) 33 without significant effect of the cardiac sodium channel isoform Na V 1.5 (IC 50 ≈2-5 μmol/L). This result therefore indicates an increased contribution of TTX-sensitive channels to I Na .…”

Hypoxic Stress Induces Transient Receptor Potential Melastatin 2 (TRPM2) Channel Expression in Adult Rat Cardiac Fibroblasts

“…To do so, we recorded the whole-cell currents from cultured cardiac fibroblasts exposed to normoxia or hypoxia for 24 h with voltage pulses between −70 and 40 mV from the holding potential of −40 mV. It has been reported that cardiac fibroblasts express multiple ion channels (14). In the present study, several types of currents were observed in different fibroblasts.…”

“…Thus, hypoxia is a pathophysiological stimulus for cardiac fibroblasts. Although cardiac fibroblasts are electrically "non-excitable" cells, various membrane currents were found in rat (9 -13) and human cardiac fibroblasts (14), including an inward rectifier K + current, a delayed rectifier K + current, and a non-selective cation current. However, the roles of those currents are not fully understood in the function of cardiac fibroblasts.…”

TGF-β 1 -Mediated Fibrosis and Ion Channel Remodeling Are Key Mechanisms in Producing the Sinus Node Dysfunction Associated With SCN5A Deficiency and Aging

“…The surprising correlation between Nav1.5 and fibrotic genes then prompted direct tests of the hypothesis that reduced Nav1.5 channel expression or activity might acutely upregulate TGF-␤ 1 and vimentin transcripts in cardiac myocytes and cardiac fibroblasts, both known to express Nav1.5. 21 Twenty-four-hour incubations with 15 g/mL Nav1.5-E3 antibody, known specifically to inhibit Nav1.5 function, 19 produced 0.9-and 1.2-fold upregulations of TGF-␤ 1 transcript in cardiac myocytes and fibroblasts, respectively, and 18-and 4.6-fold increases in active TGF-␤ 1 protein in the cell culture medium (antibody treatment versus control for either myocytes or fibroblasts, Pϭ0.04 for transcripts of myoctes, Pϭ0.03 for transcripts of fibroblasts, and PϽ0.001 for protein) ( Figure 5C). As shown in online-only Data Supplement Figure 3, such increased TGF-␤ 1 mRNA/ active form TGF-␤ 1 protein in myocytes treated with Nav1.5-E3 antibody is associated with an Ϸ20% reduction in Nav1.5 protein expression and an Ϸ50% reduction in peak i Na current density compared to nontreated cells.…”