High Ambient Pressure Produces Hypertrophy and Up-Regulates Cardiac Sarcoplasmic Reticulum Ca²⁺ Regulatory Proteins in Cultured Rat Cardiomyocytes

Abstract

Previously, we demonstrated in vivo that the nature of the alterations in sarcoplasmic reticulum (SR) function and SR Ca²⁺ regulatory proteins depends both on the type of mechanical overload imposed and on the duration of the heart disorder. The purpose of the present study was to determine in vitro whether an extrinsic mechanical overload (in the form of high ambient pressure) would cause an up-regulation of ryanodine receptor (RyR) and Ca²⁺-ATPase, as we previously reported mildly pressure-overloaded, hypertrophied rat hearts. Primary cultures of neonatal rat cardiomyocytes were prepared and high ambient pressure was produced using an incubator and pressure-overloading apparatus. Cells were exposed to one of two conditions for 72 h: atmospheric pressure conditions (APC) or high pressure conditions (HPC; HPC=APC+200 mmHg). The expression levels of RyR and Ca²⁺-ATPase were quantified and functional characteristics were monitored. The cell area was significantly greater under HPC. After 6 h exposure, the physiological properties of cardiomyocytes were impaired, but they returned to the baseline level within 24 h. After 24 h exposure, the expression level of RyR was significantly higher under HPC, and for Ca²⁺-ATPase, the expression level was significantly higher under HPC after 6 h exposure. HPC caused hypertrophy and up-regulated the expression of Ca²⁺ regulatory proteins and their genes. We suggest that this in vitro pressure-overloading model may prove useful, as is a stretch-overloading model, for investigation of the intracellular Ca²⁺ regulatory pathways responsible for the development of cardiac hypertrophy.