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Biological Research

Print version ISSN 0716-9760


RIOS, EDUARDO  and  ZHOU, JINGSONG. Control of dual isoforms of Ca2+ release channels in muscle. Biol. Res. [online]. 2004, vol.37, n.4, pp.583-591. ISSN 0716-9760.

Here we compare excitation-contraction coupling in single muscle cells of frogs and rats. Because amphibians have isoform 3 (or b) of the ryanodine receptor/Ca2+ release channel, in addition to 1 (a), which is also present in the mammal, any extra feature present in the frog may in principle be attributed to isoform 3. Ca2+ release under voltage clamp depolarization has a peak and a steady phase in both taxonomic classes, but the peak is more marked in the frog, where the ratio of amplitudes of the two phases is voltage-dependent. This dependence is a hallmark of CICR. Confocal imaging identified Ca2+ sparks in the frog, but not in the voltage-clamped rat cells. Because Ca2+ sparks involve CICR both observations indicate that the contribution of CICR is minor or null in the mammal. The "couplon" model well accounts for observations in the frog, but assumes a structure that we now know to be valid only for the rat. A revised model is proposed, whereby the isoform 3 channels, located parajunctionally, are activated by CICR and contribute its characteristic global and local features. Several issues regarding the roles of different channels remain open to further study.

Keywords : Excitation-contraction coupling; sarcoplasmic reticulum; Ca2+ sparks; ryanodine receptor; calcium-induced calcium release.

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