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1 Laboratory for Physiology, Institute for Cardiovascular Research (ICaR-VU), VU University Medical Center, Amsterdam, The Netherlands
* To whom correspondence should be addressed. E-mail: sipkema{at}physiol.med.vu.nl.
The objective of this study is to evaluate the role of right ventricular hypertrophy on developed tension and contractile reserve of rat papillary muscle, using a model of Monocrotaline-induced pulmonary hypertension. Calcium handling and influence of HCO3- ions were also addressed by using two different buffers (Bicarbonate and HEPES). Wistar rats were injected with either MCT (40 mg kg-1, s.c.) or vehicle (CON). Isometrically contracting right ventricular papillary muscles were studied at 80% of Lmax. Contractile reserve (1-Fdev/Fmax) was calculated from developed tension (Fdev) and maximal tension (Fmax). Calcium recirculation was determined with post-extrasystolic potentiation. Both groups of muscles were superfused with either Bicarbonate (CON-B and MCT-B, both n=6) or HEPES (CON-H and MCT-H, both n=6) buffer. With hypertrophy, contractions were slower but developed tension was not changed. However, maximal tension was decreased (P < 0.05). With Bicarbonate, maximal tension decreased from 23.8 ± 6.5 mN mm-2 in CON-B, to 13.7 ± 3.3 mN mm-2 in MCT-B. With HEPES it decreased from 16.3 ± 3.5 mN mm-2 (n=6, CON-H) to 8.3 ± 1.6 mN mm-2 (MCT-H). Contractile reserve during hypertrophy was therefore also decreased (P < 0.05). With Bicarbonate it decreased from 0.73 ± 0.03 (CON-B) to 0.55 ± 0.04 (MCT-B). With HEPES it decreased (P < 0.001) from 0.64 ± 0.07 (CON-H) to 0.19 ± 0.06 (MCT-H). The recirculation fraction decreased (P < 0.05) from 0.59 ± 0.04 in CON-B to 0.44 ± 0.04 in MCT-B. We conclude that contractile reserve and recirculation fraction are impaired during hypertrophy, with a stronger effect under HEPES than bicarbonate superfusion.
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