Functional role of CLC-2 chloride inward rectifier channels in cardiac sinoatrial nodal pacemaker cells

Abstract

A novel Cl − inward rectifier channel (Cl,ir) encoded by ClC-2, a member of the ClC voltage-gated Cl − channel gene superfamily, has been recently discovered in cardiac myocytes of several species. However, the physiological role of Cl,ir channels in the heart remains unknown. In this study we tested the hypothesis that Cl,ir channels may play an important role in cardiac pacemaker activity. In isolated guinea-pig sinoatrial node (SAN) cells, Cl,ir current was activated by hyperpolarization and hypotonic cell swelling. RT-PCR and immunohistological analyses confirmed the molecular expression of ClC-2 in guinea-pig SAN cells. Hypotonic stress increased the diastolic depolarization slope and decreased the maximum diastolic potential, action potential amplitude, APD 50 , APD 90 , and the cycle-length of the SAN cells. These effects were largely reversed by intracellular dialysis of anti-ClC-2 antibody, which significantly inhibited Cl,ir current but not other pacemaker currents, including the hyperpolarization-activated non-selective cationic "funny" current (I f ), the L-type Ca 2+ currents (I Ca,L ), the slowly-activating delayed rectifier I Ks and the volume-regulated outwardlyrectifying Cl − current (I Cl,vol ). Telemetry electrocardiograph studies in conscious ClC-2 knockout (Clcn2 −/− ) mice revealed a decreased chronotropic response to acute exercise stress when compared to their age-matched Clcn2 +/+ and Clcn2 +/− littermates. Targeted inactivation of ClC-2 does not alter intrinsic heart rate but prevented the positive chronotropic effect of acute exercise stress through a sympathetic regulation of ClC-2 channels. These results provide compelling evidence that ClC-2-encoded endogenous Cl,ir channels may play an important role in the regulation of cardiac pacemaker activity, which may become more prominent under stressed or pathological conditions.

The Functional Role of Chloride Channels in Cardiac Pacemaker Activity

“…Activation of ClC-2 current should mainly cause a depolarization of the resting membrane potential and it is suggested that the acidosisinduced increase in I Cl,ir might underlie the depolarization of the resting membrane potential during acidosis or hypoxia (Komukai et al, 2002a;Komukai et al, 2002b). Our recent study found that I Cl,ir was indeed functionally expressed in guinea-pig SAN cells (Huang et al, 2009). I Cl,ir in guinea-pig SAN cells activated upon cell membrane hyperpolarization and hypotonic challenge has a strong inward rectification under symmetrical Cl -conditions with a reversal potential close to the predicted value of E Cl , and is inhibited by Cd 2+ (Figure 4).…”

“…The expression of ClC-2 in the heart was further characterized by immunohistochemistry and western blot from several species . Later studies provided compelling evidence that I Cl.ir is encoded by ClC-2 and its alternatively spliced isoforms in the heart (Britton et al, 2005;Huang et al, 2009). ClC-2 channels are activated by hyperpolarization, cell swelling, and acidosis and have an inwardly rectifying I-V relationship Komukai et al, 2002a;Komukai et al, 2002b;Britton et al, 2005;Huang et al, 2009).…”

“…Later studies provided compelling evidence that I Cl.ir is encoded by ClC-2 and its alternatively spliced isoforms in the heart (Britton et al, 2005;Huang et al, 2009). ClC-2 channels are activated by hyperpolarization, cell swelling, and acidosis and have an inwardly rectifying I-V relationship Komukai et al, 2002a;Komukai et al, 2002b;Britton et al, 2005;Huang et al, 2009). During the cardiac action potential, therefore, activation of the ClC-2 channels will conduct mainly an inward current as a result of Clefflux at negative membrane potentials and cause a depolarization of the resting membrane potential of cardiac cells.…”

A Meta-Analysis of Acupuncture Use in the Treatment of Cognitive Impairment After Stroke

“…The 21 included trials 22,[26][27][28][29][30][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] were conducted in China and included a total of 1421 patients ranging in age from 18 to 80 years. More male than female participants were included in 15 trials, while four trials did not describe the sex of the patients.…”

“…Four trials with a total of 116 patients 30,46,50,51 measured improved MMSE total scores after 4-week acupuncture treatment. Heterogeneous tests were performed on the four referred trials.…”