Sarcoplasmic reticulum Ca2+ regulatory protein gene expression in human right atrium under hemodynamic overload

Pulmonary artery banding alters the expression of Ca2+ transport proteins in the right atrium in rabbits

Following pulmonary artery banding (PAB), the contractile function of right ventricle diminishes over time. Subsequently, the right atrium (RA) has to contract against a higher afterload, but it is unknown to what extent ventricular dysfunction has an effect on the atrial contractility. We hypothesized that right ventricular pressure overload may have an affect on atrial contractility and Ca(2+) transport protein expression. Therefore, we induced pressure overload of the right ventricle by PAB for 10 wk in rabbits and examined the changes in the expression of Ca(2+) transport proteins in the atrium. We demonstrate that PAB significantly decreased the expression of sarco(endo)plasmic reticulum Ca(2+)-ATPase (Serca) 2a while expression of Na(+)/Ca(2+) exchanger-1 was significantly upregulated in the RA but not in the left atria of rabbit hearts, indicating that pressure is the major trigger. A decrease in Serca2a expression was concomitant with a significant decrease in sarcolipin (SLN), possibly indicating a compensatory role of SLN. The decreased expression of SLN was unable to completely restore sarcoplasmic reticulum Ca(2+) uptake function of Serca2a. Functional contractile assessments in isolated trabeculae showed no difference between PAB- and sham-operated rabbits at 1 Hz but displayed an enhanced force development at higher frequencies and in the presence of isoproterenol, while twitch timing was unaffected. Our results indicate that right ventricular mechanical overload due to PAB affects the expression of the Ca(2+)-handling proteins in the RA in rabbits.

Mechanical stress-dependent transcriptional regulation of sarcolipin gene in the rodent atrium

Sarcolipin, a homologue of phospholamban, regulates Ca2+ uptake through the interaction with sarcoplasmic reticulum Ca2+ ATPase (SERCA) and is predominantly expressed in the atrial muscle. Although the atrial chamber-specific expression of sarcolipin could be primarily regulated at the transcriptional level, the transcriptional regulation remains poorly understood. Since mechanical stress plays an important role in transcriptional regulation of a gene involved in cardiac hypertrophy and remodeling, we generated left-sided or right-sided pressure-overload models by transverse aortic constriction (TAC) in ddY mice or by monocrotaline administration in Wistar rats, respectively. TAC significantly decreased the expression of sarcolipin, SERCA2a, and phospholamban mRNAs in the left atrium (LA) than those in the right atrium (RA). By contrast, monocrotaline administration significantly decreased the expression of sarcolipin, SERCA2a, and phospholamban mRNAs in the RA than those in the LA. The two independent complementary experiments unequivocally demonstrated that mechanical stress down-regulates the transcription of the sarcolipin gene.