Rachel E. Milner

Calcium binding proteins in the sarcoplasmic/endoplasmic reticulum of muscle and nonmuscle cells

In this paper we review some of the large quantities of information currently available concerning the identification, structure and function of Ca2+-binding proteins of endoplasmic and sarcoplasmic reticulum membranes. The review places particular emphasis on identification and discussion of Ca2+ ‘storage’ proteins in these membranes. We believe that the evidence reviewed here supports the contention that the Ca2+-binding capacity of both calsequestrin and calreticulin favor their contribution as the major Ca2+-binding proteins of muscle and nonmuscle cells, respectively. Other Ca2+-binding proteins discovered in both endoplasmic reticulum and sarcoplasmic reticulum membranes probably contribute to the overall Ca2+ storage capacity of these membrane organelles, and they also play other important functional role such as posttranslational modification of newly synthesized proteins, a cytoskeletal (structural) function, or movement of Ca2+ within the lumen of the sarcoplasmic/endoplasmic reticulum towards the storage sites.

Using Clickers to Improve Student Engagement and Performance in an Introductory Biochemistry Class.

As part of ongoing efforts to enhance teaching practices in a large‐class introductory biochemistry course, we have recently tested the effects of using a student response system (clickers) on student exam performances and engagement with the course material. We found no measurable difference in class mean composite examination score for students taught with clickers than for those taught in traditional lectures. However, there were significantly more students in the highest achievement category (91–100%) in the section that incorporated clickers than in any other section over five academic terms. Overall, students gave high approval ratings for the use of the clickers, particularly in increasing their participation and engagement in lectures. However, students who reported their performance to be in the lowest performance categories gave a lower level of approval for the use of the clickers than those who reported their performance to be in the higher performance categories. The implications for using clickers to improve teaching in biochemistry are discussed.

Seasonal variations in the rate and capacity of cardiac SR calcium accumulation in a hibernating species

The rate of calcium uptake and the level of calcium accumulation was measured in cardiac muscle SR from hibernating and nonhibernating Richardsons ground squirrels. In whole heart homogenates, the rate of calcium uptake was higher (P less than 0.05) in hibernating animals than it was in active animals. Further purification of homogenates into sacroplasmic reticulum (SR) preparations showed that the hibernating animals had the highest rate of calcium uptake and the greatest level of calcium accumulation. These results could not be explained by variations in non-SR membrane contaminants nor by changes in the maximal activity or total amount of a SR marker enzyme, the Ca(2+)-ATPase. The addition of ryanodine to the calcium uptake medium increased the level of calcium accumulation in all groups by a similar amount. It is concluded that the high rate of calcium uptake by isolated cardiac SR vesicles from hibernating ground squirrels reflects the activity of the organelle in vivo, and that the ability of the ryanodine-insensitive population of SR vesicles to accumulate calcium is affected by hibernation.

Phosphorylation of the carboxyl terminal region of dystrophin by mitogen-activated protein (MAP) kinase

Dystrophin is the 427-kDa protein product of the Duchenne muscular dystrophy gene (DMD). The function of this protein remains to be elucidated. We have recently reported that dystrophin is phosphorylated,in vivo, in rat skeletal muscle primary cell culture (RE Milner, JL Busaan, CFB Holmes, JH Wang, M Michalak (1993) J Biol Chem 268: 21901–21905). This observation suggests that protein phosphorylation may have some role in modulating the function of dystrophin or its interaction with membrane associate dystroglycan. We report here that the carboxyl-terminal of dystrophin is phosphorylated by the MAP kinase p44mpk (mitogen-activated protein kinase), from the sea star oocytes and by soluble extracts of rabbit skeletal muscle. Importantly we showed that native dystrophin in isolated sarcolemmal vesicles is phosphorylated by sea star p44mpk. Partial purification and immunological analysis show that a mammalian kinase related to p44mpk is present in the skeletal muscle extracts and that it contributes to phosphorylation of the carboxyl-terminal of dystrophin. This kinase phosphorylates dystrophin on a threonine residue(s). We conclude that phosphorylation of dystrophin may play an important role in the function of this cytoskeletal protein.

Effects of high fat diets on hibernation and adipose tissue in Turkish hamsters

SummaryThe effects of dietary fat saturation and fat content on hibernation and several properties of white and brown adipose tissue (WAT and BAT, respectively) were investigated in Turkish hamsters (Mesocricetus brandti). Male hamsters were housed in a long photoperiod (LD 16:8) at 23°C and fed one of three diets: (1) chow (6.5% fat per weight), (2) chow+13.5% vegetable oil (OIL, 20% fat per weight [largely unsaturated fat]) and (3) chow+13.5% vegetable shortening [SHORTENING, 20% fat per weight (largely saturated fat)]. Five weeks later body weights had stabilized and the animals were transferred to a short photoperiod (LD 8:16) at 3°C. At the peak of the hibernation season (17 weeks) the animals were sacrificed within 24 h of arousal. Chow-fed hamsters had the greatest percentage of animals hibernating and days found torpid compared with the two fat-fed groups, with no differences found between the latter two groups for these measures. There were no differences between hibernating (HIB) and nonhibernating (NON-HIB) hamsters across or within the diet groups for any of the BAT measures [uncoupling protein content, mitochondrial mass, lipoprotein lipase (LPL) activity, and in vivo lipogenesis], nor were there significant effects of the diet on these measures. CHOW-and OIL-fed HIB hamsters showed decreases in body weight. All HIB groups had decreases in each carcass component, several fat pad weights, testes weight, and food intake. No consistent differences in WAT LPL activity or in vivo lipogenesis were found between HIB and NON-HIB hamsters. Feeding saturated high fat diets inhibits hibernation in some species; however, in the present experiment, feeding of both saturated and unsaturated fat-laden diets inhibited hibernation to a similar degree.