EFFECTS OF ELECTRICAL-STIMULATION AND POSTMORTEM STORAGE ON CHANGES IN TITIN, NEBULIN, DESMIN, TROPONIN-T, AND MUSCLE ULTRASTRUCTURE IN BOS-INDICUS CROSSBRED CATTLE

The effects of electrical stimulation (ES) on degradation of titin, ne bulin, desmin, and troponin-T (TN-T) and on structural changes in the longissimus muscle (LM) from Brahman x Simmental (B x S) cattle (Bos i ndicus;cross) were determined. The left side of seven B x S beef carca sses was stimulated (200 V, 20 Hz) within 1 h of death, and the right side was the nonstimulated (NS) control. Myofibrils for SDS-PAGE and s amples for transmission electron microscopy were prepared from the LM at 0, 1, 3, 7, 14, and 28 d postmortem (PM). The SDS-PAGE results show ed that the T1 band of titin was absent by 7 d in two animals, by 14 d in four animals, and by 28 d in one animal in both NS and ES samples. By SDS-PAGE, intact nebulin was gone by 7 d in two animals and by 14 d in five animals, but in blots, nebulin decreased by 7 d and was abse nt by 14 d in both NS and ES samples. The desmin band could still be s een as a light band at 28 d in Western blots of both NS and ES samples . A decrease in TN-T and a concomitant increase in the 30-kDa polypept ide were observed in both NS and ES samples. Western blots with a mono clonal antibody to TN-T confirmed that TN-T decreased at similar rates in NS and ES samples but showed that the 30-kDa polypeptide was more heavily labeled in ES samples from 7 to 28 d. Contraction nodes were p resent in 0-d ES samples and were still observed in 28-d ES samples. N arrow, intermediate, and wide I-band fractures were seen earlier and a t a greater frequency in ES than in NS samples. Overall, ES had no det ectable effect on titin, nebulin, desmin, or TN-T degradation but acce lerated the appearance and enhanced the frequency of three types of I- band fractures in the LM from Bos indicus crossbred cattle.