Transmural differences in the expression of Ca²⁺ handling proteins have been observed in normal mammalian myocardium. This pattern of expression may be altered in hypertrophic myocardium. In this study, a rabbit coronary artery ligation model of left ventricular dysfunction (LVD) was used to induce cardiac hyper-trophy. Transmural protein expression of sarcoplasmic-endoplasmic reticulum Ca²⁺-ATPase (SERCA), Calsequestrin (CSQ) and Na⁺-Ca²⁺ exchanger (NCX) were measured in left ventricular (LV) tissue samples isolated from LVD and sham-operated rabbit hearts.

Hearts were removed under terminal anaesthetic (100 mg kg^-1 Euthatal) 8 weeks after left circumflex coronary artery ligation. Tissue was dissected from basal endocardial (ENDO) and epicardial (EPI) regions of LV free wall, homogenised and prepared for Western blot analysis. SDS-PAGE was performed and proteins were transferred onto nitrocellulose membranes. These membranes were hybridised with antibodies to detect SERCA2 (monoclonal, 1: 20 000, Affinity Bioreagents), NCX (antiserum 1: 5 000, Swant) and CSQ (monoclonal, 1: 80 000, Swant). Gels were loaded to enable direct comparisons of ENDO vs.EPI and sham vs. LVD changes. In separate experiments, crude SR membrane fractions were prepared from homogenised transmural LV samples. Total SR protein was measured from sham and LVD samples. Data (means and S.E.M.) were analysed using Student’s t test and a P value < 0.05 was considered significant.

In both experimental groups (sham and LVD), a small transmural gradient in CSQ expression was observed. ENDO regions (n = 20, sham; 20, LVD) showed a slightly higher CSQ expression compared with EPI (n = 20, sham; 20, LVD). In general, LVD tissue showed an overall increase in CSQ expression compared with sham (not statistically significant). Combining both ENDO and EPI data, CSQ expression was significantly higher (139 ± 13 %, P = 0.002, n = 42) in the LVD. No transmural SERCA expression was observed in either experimental group. Tissue isolated from LVD ENDO and EPI (n = 17) regions showed a small decrease in SERCA expression (8 ± 1 %). A small transmural difference in NCX expression was observed; sham EPI samples were 86 ± 10 % (n = 20) of sham ENDO. In LVD there was a trend towards higher NCX expression although this did not reach statistical significance. Total SR protein (mg (g wet weight)^-1) was higher in LVD (0.84 ± 0.27, n = 46) in comparison with sham (0.66 ± 0.26, P < 0.001, n = 24).

These data suggest that of the three proteins studied, CSQ expression showed the most significant changes in LVD. LVD samples showed a small decrease in SERCA levels and a slight increase in NCX levels in comparison with sham samples. The upregulation of CSQ expression in this model of LVD may be partially responsible for the increase in total protein in SR membrane fractions isolated from LVD hearts.

This work was supported by the British Heart Foundation.