Resting membrane potential and intracellular [Na] at rest, during fatigue and during recovery in rat soleus muscle fibres in situ.

Large trans-sarcolemmal ionic shifts occur with fatiguing exercise or stimulation of isolated muscles. However, it is unknown how resting membrane potential (E) and intracellular sodium concentration ([Na]) change with repeated contractions in living mammals. We investigated (i) whether [Na] (peak, kinetics) can reveal changes of Na-K pump activity during brief or fatiguing stimulation and (ii) how resting E and [Na] change during fatigue and recovery of rat soleus muscle in situ.

Stretch Harmonizes Sarcomere Strain Across the Cardiomyocyte.

Background: Increasing cardiomyocyte contraction during myocardial stretch serves as the basis for the Frank-Starling mechanism in the heart. However, it remains unclear how this phenomenon occurs regionally within cardiomyocytes, at the level of individual sarcomeres. We investigated sarcomere contractile synchrony and how intersarcomere dynamics contribute to increasing contractility during cell lengthening.

AKAP18δ Anchors and Regulates CaMKII Activity at Phospholamban-SERCA2 and RYR.

Background: The sarcoplasmic reticulum (SR) Ca-ATPase 2 (SERCA2) mediates Ca reuptake into SR and thereby promotes cardiomyocyte relaxation, whereas the ryanodine receptor (RYR) mediates Ca release from SR and triggers contraction. Ca/CaMKII (CaM [calmodulin]-dependent protein kinase II) regulates activities of SERCA2 through phosphorylation of PLN (phospholamban) and RYR through direct phosphorylation. However, the mechanisms for CaMKIIδ anchoring to SERCA2-PLN and RYR and its regulation by local Ca signals remain elusive.

Design of a Proteolytically Stable Sodium-Calcium Exchanger 1 Activator Peptide for Studies.

The cardiac sodium-calcium exchanger (NCX1) is important for normal Na- and Ca-homeostasis and cardiomyocyte relaxation and contraction. It has been suggested that NCX1 activity is reduced by phosphorylated phospholemman (pSer68-PLM); however its direct interaction with PLM is debated. Disruption of the potentially inhibitory pSer68-PLM-NCX1 interaction might be a therapeutic strategy to increase NCX1 activity in cardiac disease.