Role of the sarcoplasmic reticulum in calcium dynamics of the ventricular myocardium of Lepidosiren paradoxa (Dipnoi) at different temperatures
✍ Scribed by M.J Costa; C.D Olle; A.L Kalinin; F.T Rantin
- Publisher
- Elsevier Science
- Year
- 2004
- Tongue
- English
- Weight
- 272 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0306-4565
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✦ Synopsis
This study analyzed the impact of changes in stimulation frequency on the inotropic responses of the South American lungfish Lepidosiren paradoxa ventricle strips. The effects of prolonged diastolic pauses and stepwise increases in stimulation frequency upon force development were determined at different temperatures (15 C, 25 C, and 35 C) and in response to 10 mM of ryanodine. A post-rest potentiation of force was observed only at 15 C, but ryanodine was able to depress twitch force at low stimulation frequencies, irrespective of temperature. Moreover, when in vivo stimulation frequencies were reached, the sarcoplasmic reticulum was relevant to the Ca 2+ management only at 15 C and 25 C. In contrast, the lack of effect of ryanodine at the in vivo frequencies at 35 C indicates that the excitation-contraction coupling depends exclusively on the transarcolemmal Ca 2+ influx. Therefore, this organelle seems to have a slower Ca 2+ -cycling capacity, in spite of being anatomically well developed and potentially functional in all the temperatures tested.