Excitation-contraction coupling properties in women with work-related myalgia: a preliminary study

We investigated the potential role of selected excitation-contraction coupling processes in females with work-related myalgia (WRM) by comparing WRM with healthy controls (CON) using tissue from extensor carpi radialis brevis (ECRB) and trapezius (TRAP) muscles. For the ECRB, age (mean ± SE) was 29.6 ± 3.5 years for CON (n = 9) and 39.2 ± 2.8 years for WRM (n = 13), while for the TRAP, the values were 26.0 ± 2.1 years for CON (n = 7) and 44.6 ± 2.9 years for WRM (n = 11). For the sarcoplasmic reticulum (SR) of the ECRB, WRM displayed concentrations (nmol·(mg protein)(-1)·min(-1)) that were lower (P < 0.05) for Total (202 ± 4.4 vs 178 ± 7.1), Basal (34 ± 1.6 vs 30.1 ± 1.3), and maximal Ca(2+)-ATPase activity (Vmax, 168 ± 4.9 vs 149 ± 6.3), and Ca(2+)-uptake (5.06 ± 0.31 vs 4.13 ± 0.29), but not SERCA1a and SERCA2a isoforms, by comparison with CON. When age was incorporated as a co-variant, Total, Basal, and Ca(2+)-uptake remained different from CON (P < 0.05), but not Vmax (P = 0.13). For TRAP, none of the ATPase properties differed between groups (P > 0.05) either before or following adjustment for age. No differences (P > 0.05) were observed between the groups for Ca(2+)-release in the SR for either TRAP or ECRB. Similarly, no deficiencies, regardless of muscle, were noted for either the Na(+)-K(+)-ATPase content or the α and β subunit isoform distribution in WRM. This preliminary study provides a basis for further research, with expanded numbers, investigating the hypothesis that abnormalities in SR Ca(2+)-regulation are involved in the cellular etiology of WRM.