EXPRESSION OF SARCOPLASMIC-RETICULUM CA2-ACCLIMATING DUCKLINGS( TRANSPORT PROTEINS IN COLD)

The relationship between the cold-induced increase in sarcoplasmic ret iculum (SR) Ca2+ transport proteins and the development of muscular no nshivering thermogenesis (NST) was investigated by determining the tim e course of expression of the sarcoplasmic or endoplasmic reticulum Ca 2+-ATPase (SERCA), Ca2+ release channel, and calsequestrin in control and cold-acclimating ducklings. Ca-45(2+) uptake and [H-3]ryanodine bi nding measurements with skeletal muscle homogenates showed that a cold acclimation period of similar to 4 wk was required to observe a subst antial increase in Ca2+-ATPase activity and Ca2+ release channel conte nt, which correlates well with NST development. Immunoblot analysis of muscle homogenates showed no differences in calsequestrin levels but revealed that the decrease in SERCA2a content was delayed in cold-accl imating birds and that the SERCA1 level was increased after 4 wk of co ld acclimation. The persistence of SERCA2a may be related to shivering thermogenesis occurring preferentially in slow-twitch fibers. SERCA1 may account for most of the cold-induced increase in Ca-45(2+) uptake activity, suggesting the preferential occurrence of a Ca2+-dependent N ST in fast-twitch fibers.