PKA phosphorylation underlies functional recruitment of sarcolemmal SK2 channels in ventricular myocytes from hypertrophic hearts

Abstract

Key points Small‐conductance Ca 2+ ‐activated K + (SK) channels expressed in ventricular myocytes are dormant in health, yet become functional in cardiac disease. SK channels are voltage independent and their gating is controlled by intracellular [Ca 2+ ] in a biphasic manner. Submicromolar [Ca 2+ ] activates the channel via constitutively‐bound calmodulin, whereas higher [Ca 2+ ] exerts inhibitory effect during depolarization. Using a rat model of cardiac hypertrophy induced by thoracic aortic banding, we found that functional upregulation of SK2 channels in hypertrophic rat ventricular cardiomyocytes is driven by protein kinase A (PKA) phosphorylation. Using site‐directed mutagenesis, we identified serine‐465 as the site conferring PKA‐dependent effects on SK2 channel function. PKA phosphorylation attenuates I SK rectification by reducing the Ca 2+ /voltage‐dependent inhibition of SK channels without changing their sensitivity to activating submicromolar [Ca 2+ ] i . This mechanism underlies the functional recruitment of SK channels not only in cardiac disease, but also in normal physiology, contributing to repolarization under conditions of enhanced adrenergic drive. Abstract Small‐conductance Ca 2+ ‐activated K + (SK) channels expressed in ventricular myocytes (VMs) are dormant in health, yet become functional in cardiac disease. We aimed to test the hypothesis that post‐translational modification of SK channels under conditions accompanied by enhanced adrenergic drive plays a central role in disease‐related activation of the channels. We investigated this phenomenon using a rat model of hypertrophy induced by thoracic aortic banding (TAB). Western blot analysis using anti‐pan‐serine/threonine antibodies demonstrated enhanced phosphorylation of immunoprecipitated SK2 channels in VMs from TAB rats vs . Shams, which was reversible by incubation of the VMs with PKA inhibitor H89 (1 μmol L –1 ). Patch clamped VMs under basal conditions from TABs but not Shams exhibited outward current sensitive to the specific SK inhibitor apamin (100 nmol L –1 ), which was eliminated by inhibition of PKA (1 μmol L –1 ). Beta‐adrenergic stimulation (isoproterenol, 100 nmol L –1 ) evoked I SK in VMs from Shams, resulting in shortening of action potentials in VMs and ex vivo ...

Impact of arrhythmogenic calmodulin variants on small conductance Ca 2+ ‐activated K + (SK3) channels

“…As SK channels appears to play a role in some pathological conditions in the ventricles (Gui ; Bonilla ; Hundahl ; Chen ; Hamilton ), it could be speculated that the SK channels also have a contributory role in the pathogenesis of CaM‐associated LQTS. Three out of the four LQTS‐associated CaM variants significantly down‐regulated the SK current, with CaM D130G being the variant most profoundly decreasing SK current with no effect on the trafficking of the channel.…”

“…This atrial selectivity makes SK channels an interesting target in the treatment of atrial arrhythmias, as the ventricular side effects have been speculated to be avoided (Xu ; Diness , ; Skibsbye ; Skibsbye ). However, several recent studies have shown that SK channel current also becomes functional in the ventricles during enhanced sympathetic activation through β ‐adrenergic stimulation (Chen ; Hamilton ).…”

Small and Intermediate Calcium Activated Potassium Channels in the Heart: Role and Strategies in the Treatment of Cardiovascular Diseases

“…This regulation seems C-terminal specific, since SK trafficking is not altered when the three "major" Serine residues are replaced by non-phosphorable amino acids. On the other hand, PKA phosphorylation of the fourth carboxyl Serine is associated with a functional upregulation of SK2 in hypertrophic rat cardiomyocytes (Hamilton et al, 2020). In murine colonic myocytes, the open probability of SK channels is increased after phosphorylation by calmodulin kinase II (Kong et al, 2000).…”

Delayed global feedback in the genesis and stability of spatiotemporal excitation patterns in paced biological excitable media

“…I SK is an outward current which also increases with the intracellular Ca 2+ concentration, and thus I SK promotes negative Ca 2+ -to-APD coupling. Under normal conditions, I SK only presents in atrial myocytes, but under heart failure, it also presents in ventricular myocytes [ 51 – 53 ]. Since the charge carriers of both currents are not Ca 2+ , unlike I Ca and I NCX , they do not directly affect intracellular Ca 2+ dynamics.…”