Contractile reserve but not tension is reduced in monocrotaline-induced right ventricular hypertrophy

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Abstract
The objective of this study was to evaluate the role of right ventricular hypertrophy on developed tension (Fdev) and contractile reserve of rat papillary muscle by using a model of monocrotaline (Mct)-induced pulmonary hypertension. Calcium handling and the influence of bicarbonate ([Formula: see text]) were also addressed with the use of two different buffers ([Formula: see text] and HEPES). Wistar rats were injected with either Mct (40 mg/kg sc) or vehicle control (Con). Isometrically contracting right ventricular papillary muscles were studied at 80% of the length of maximal developed force. Contractile reserve (1 – Fdev/Fmax) was calculated from Fdev and maximal tension (Fmax). Calcium recirculation was determined with postextrasystolic potentiation. Both groups of muscles were superfused with either [Formula: see text] (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 Fdev was not changed. However, Fmax was decreased ( P < 0.05). With [Formula: see text], Fmax 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 [Formula: see text], 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 [Formula: see text] superfusion.

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