Reduced density and altered regulation of rat atrial L-type Ca²⁺current in heart failure

Abstract

Bond RC, Bryant SM, Watson JJ, Hancox JC, Orchard CH, James AF. Reduced density and altered regulation of rat atrial L-type Ca 2ϩ current in heart failure. Am J Physiol Heart Circ Physiol 312: H384 -H391, 2017. First published December 6, 2016; doi:10.1152/ ajpheart.00528.2016.-Constitutive regulation by PKA has recently been shown to contribute to L-type Ca 2ϩ current (ICaL) at the ventricular t-tubule in heart failure. Conversely, reduction in constitutive regulation by PKA has been proposed to underlie the downregulation of atrial ICaL in heart failure. The hypothesis that downregulation of atrial ICaL in heart failure involves reduced channel phosphorylation was examined. Anesthetized adult male Wistar rats underwent surgical coronary artery ligation (CAL, Nϭ10) or equivalent sham-operation (Sham, Nϭ12). Left atrial myocytes were isolated~18 wk postsurgery and whole cell currents recorded (holding potentialϭ-80 mV). ICaL activated by depolarizing pulses to voltages from -40 to ϩ50 mV were normalized to cell capacitance and current density-voltage relations plotted. CAL cell capacitances were~1.67-fold greater than Sham (P Յ 0.0001). Maximal ICaL conductance (Gmax) was downregulated more than 2-fold in CAL vs. Sham myocytes (P Ͻ 0.0001). Norepinephrine (1 mol/l) increased Gmax Ͼ50% more effectively in CAL than in Sham so that differences in ICaL density were abolished. Differences between CAL and Sham Gmax were not abolished by calyculin A (100 nmol/l), suggesting that increased protein dephosphorylation did not account for ICaL downregulation. Treatment with either H-89 (10 mol/l) or AIP (5 mol/l) had no effect on basal currents in Sham or CAL myocytes, indicating that, in contrast to ventricular myocytes, neither PKA nor CaMKII regulated basal ICaL. Expression of the L-type ␣1C-subunit, protein phosphatases 1 and 2A, and inhibitor-1 proteins was unchanged. In conclusion, reduction in PKA-dependent regulation did not contribute to downregulation of atrial ICaL in heart failure. NEW & NOTEWORTHY Whole cell recording of L-type Ca 2ϩcurrents in atrial myocytes from rat hearts subjected to coronary artery ligation compared with those from sham-operated controls reveals marked reduction in current density in heart failure without change in channel subunit expression and associated with altered phosphorylation independent of protein kinase A. atrial remodeling; coronary artery ligation; voltage-gated Ca 2ϩ channel ATRIAL FIBRILLATION (AF) is the most common clinical arrhythmia and is associated with significant mortality, primarily through stroke and heart failure (2, 3). There are many causes of AF and although patients generally show multiple predisposing risk factors, Ͼ70% of patients have some form of underlying structural heart disease (2, 3). Evidence from animal models of heart diseases that predispose to AF indicates that disease-associated remodeling of the atria, presumably due to mechanical overload of the atrial wall, creates an arrhythmic substrate in which AF is more likely to arise and be sustained ...

Ion currents, action potentials, and noradrenergic responses in rat pulmonary vein and left atrial cardiomyocytes

“…All procedures were conducted in accordance with UK legislation, were approved by the University of Bristol Animal Welfare and Ethics Review Board and were conducted in accordance with the ARRIVE Guidelines. LA cardiomyocytes were isolated following retrograde perfusion of the aorta with a collagenase‐containing Tyrode's solution (Type 1, Worthington, 205–351 U/mg) using a modified Langendorff apparatus, as follows (Bond et al., 2014, 2017). Following general anesthesia (intraperitoneal injection of 60–100 mg/kg sodium pentobarbital and 625 international units (IU) of heparin), the heart was excised rapidly and placed in a dunk beaker containing solution A (see below) plus 750 μM CaCl 2 and 10 IU of heparin (pH 7.4, room temperature, ~22°C).…”

Atrial fibrillation promotion in a rat model of heart failure induced by left ventricle radiofrequency ablation

“…Expression of Ca v 1.2 and connexin 43 remained significantly decreased in animals treated with spironolactone. Atrial L-type Ca 2+ current is downregulated in heart failure changing action potential configuration and refractoriness [ 2 , 6 ]. In addition, abnormal atrial Ca 2+ handling occurs in heart failure [ 24 , 25 ] and other AF models like spontaneously hypertensive rats [ 26 ] and contribute to the development of ectopic activity.…”

“…These abnormalities promote slow local conduction favoring sustained reentry. In addition, heart failure-induced atrial remodeling is commonly associated with reduced expression of L-type Ca 2+ channels which may change action potential configuration and atrial refractoriness [ 6 ]. It has been shown in animal models that mineralocorticoid receptor blockers such as spironolactone and eplerenone, which exhibit potent antifibrotic properties, attenuate CHF-induced atrial fibrosis and atrial tachyarrhythmias [ 1 , 7 , 8 ].…”

Loss of caveolin-3-dependent regulation ofICain rat ventricular myocytes in heart failure

“…All procedures were performed in accordance with United Kingdom legislation and approved by the University of Bristol Ethics Committee. This study was conducted in parallel with other investigations using cells from the same animals to investigate ventricular and atrial cellular remodeling in heart failure and thereby conformed with the reduction component of the 3Rs (“replace, reduce, refine”) ( 3 , 6 , 16 ). Adult male Wistar rats (~250 g) were subjected to either ligation of the left anterior descending coronary artery (CAL; 10 animals) or equivalent surgery without ligation (sham; 12 animals).…”

“…Operations were conducted under general anesthesia [ketamine (75 mg/kg) and medetomidine (0.5 mg/kg ip)] with appropriate analgesia [buprenorphine (0.05 mg/kg sc)], as previously described ( 6 ). Data regarding changes in cardiac morphology and function as well as in cell morphology in these groups of animals have been previously published ( 3 , 6 ).…”