The neonatal sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA1b): a neglected pump in scope.

The neonatal isoform of the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase (SERCA1b) is formed by developmental splicing and expressed fully only in developing muscle. As a major Ca(2+) pump in myotubes, SERCA1b must be detected in excitation contraction coupling or in store-operated calcium entry. The available pan SERCA1 antibodies also recognise SERCA1b but these are more frequently used to detect SERCA1a, the adult muscle-specific isoform characteristically expressed in fast fibres of skeletal muscle. In such applications, the pan SERCA1 antibodies are frequently claimed to be SERCA1a antibodies without proving it. Realistically, such an antibody cannot be made since it should recognise a single glycine at the C-terminal, the only part of SERCA1a that is different from SERCA1b. The false interpretation of the antibody specificity created inconsistence in the literature and led to false conclusions attributing features only to SERCA1a although those at least are also shared by SERCA1b. In contrast, a SERCA1b antibody has been made against the eight amino acid peptide tail that replaces the glycine of SERCA1a at the C-terminal. Therefore, the expression of SERCA1b can be specifically demonstrated, unlike that of SERCA1a, in various stages and conditions of skeletal muscle. This review argues against misbeliefs related to the distinction, expressions and functions of the two muscle-specific SERCA1 isoforms.