Pyruvate restores β-adrenergic sensitivity of L-type Ca²⁺channels in failing rat heart: role of protein phosphatase

Abstract

Oxidative stress plays a major role in the pathogenesis of heart failure, where the contractile response to β-adrenergic stimulation is profoundly depressed. This condition involves L-type Ca(2+) channels, but the mechanisms underlying their impaired adrenergic regulation are unclear. Thus the present study explored the basis for impaired adrenergic control of Ca(2+) channels in a rat infarction model of heart failure. Patch-clamp recordings of L-type Ca(2+) current (I(Ca,L)) from ventricular myocytes isolated from infarcted hearts showed a blunted response to intracellular cAMP that was reversed by treatment with exogenous pyruvate. Biochemical studies showed that basal and cAMP-stimulated protein kinase A activities were similar in infarcted and sham-operated hearts, whereas molecular analysis also found that binding of protein kinase A to the α(1C) subunit of voltage-gated Ca(2+) channel isoform 1.2 was not different between groups. By contrast, protein phosphatase 2A (PP2A) activity and binding to α(1C) were significantly less in infarcted hearts. The PP2A inhibitor okadaic acid markedly increased I(Ca,L) in sham-operated myocytes, but this response was significantly less in myocytes from infarcted hearts. However, pyruvate normalized I(Ca,L) stimulation by okadaic acid, and this effect was blocked by inhibitors of thioredoxin reductase, implicating a functional role for the redox-active thioredoxin system. Our data suggest that blunted β-adrenergic stimulation of I(CaL) in failing hearts results from hyperphosphorylation of Ca(2+) channels secondary to oxidation-induced impairment of PP2A function. We propose that the redox state of Ca(2+) channels or PP2A is controlled by the thioredoxin system which plays a key role in Ca(2+) channel remodeling of the failing heart.

Regulation of Ca2+ transient by PP2A in normal and failing heart

“…Phosphatases, especially PP2A can make them more responsive to β-adrenergic signals by bringing down phosphorylation levels. Recent studies by Zheng et al suggest that pyruvate restores β-adrenergic sensitivity of L-type Ca 2+ channels in failing rat heart through PP2A (Zheng et al, 2013 ).…”

Dynamic Changes in Ion Channels during Myocardial Infarction and Therapeutic Challenges

“…After MI in rats, a decrease in LTCC density was detected using a whole-cell patch clamp [ 43 ]. Impaired LTCC function further leads to a reduced sensitivity of cardiomyocytes to β-adrenergic stimulation [ 44 ]. Using super-resolution scanning patch-clamp techniques, Jose L. Sanchez Alonso et al detected that functional LTCCs were dislocated to the sarcolemmal surface in failing cardiomyocytes and that these repositioned LTCCs exhibited a higher open probability (Po) and phosphorylated state.…”

Redox Regulation of Ion Channels in the Pulmonary Circulation

“…Oxidative stress also plays a major role in the pathogenesis of heart failure, and this condition involves L-type Ca 2+ channels. Zheng et al have very recently shown that the redox state of Ca 2+ channels is controlled by the thioredoxin system which plays a key role in Ca 2+ channel remodeling of the failing heart ( 187 ). Furthermore, NO also modulates VDCC by a direct redox-dependent stimulation.…”