Calcium removal in isolated rat ventricular myocytes was primarily mediated by the sarcoplasmic reticulum (87%), followed by Na-Ca exchange (8.7%), sarcolemmal Ca-ATPase (2.6%), and mitochondria (1.7%).
In rat ventricular myocytes, the sarcoplasmic reticulum accounts for 87% of calcium removal during relaxation, while Na-Ca exchange accounts for 67% of the remaining non-SR mediated removal, highlighting a greater role for Ca-ATPase compared to rabbit models.
OBJECTIVE: The aim was to estimate the relative contributions of the various intracellular and sarcolemmal systems to the relaxation of the systolic calcium transient. METHODS: The experiments were performed on isolated rat ventricular myocytes. The cells were loaded with the fluorescent indicator indo-1 in order to measure Ca2+i. RESULTS: The application of caffeine to release calcium from the sarcoplasmic reticulum produced a rise of Ca2+i which decayed about 7-8 times more slowly than the electrically stimulated calcium transient. This suggests that the sarcoplasmic reticulum accounts for about 87% of the calcium removal. The rate of decay of the caffeine response was decreased to about 33% of the control by inhibiting the Na-Ca exchange with Ni2+. In the presence of Ni2+ the rate could be inhibited further by inhibiting either the sarcolemmal Ca-ATPase (by increasing extracellular calcium concentration, Ca2+o) or the mitochondria (with FCCP and oligomycin). The relative contributions of the various processes were estimated to be: sarcoplasmic reticulum 87%, mitochondria 1.7%, Na-Ca 8.7%, sarcolemmal Ca-ATPase 2.6%. CONCLUSIONS: These experiments show that the Na-Ca exchange accounts for 67% of the calcium removal not mediated by the sarcoplasmic reticulum. This is a smaller fraction than in rabbit cardiac cells and highlights the importance of the Ca-ATPase in the rat heart.
Negretti et al. (1993) studied Isolated rat ventricular myocytes. Caffeine and various inhibitors (Ni2+, FCCP, oligomycin) vs. Control (electrically stimulated calcium transient) was evaluated on Relative contributions of intracellular and sarcolemmal systems to the relaxation of the systolic calcium transient. Calcium removal in isolated rat ventricular myocytes was primarily mediated by the sarcoplasmic reticulum (87%), followed by Na-Ca exchange (8.7%), sarcolemmal Ca-ATPase (2.6%), and mitochondria (1.7%).