How fish power swimming

It is thought that fish generate the power needed for steady swimming with their anterior musculature, whereas the posterior musculature only transmits forces to the tail and does negative work. Isolated red muscle bundles driven through the length changes and stimulation pattern that muscles normally undergo during steady swimming showed the opposite pattern. Most of the power for swimming came from muscle in the posterior region of the fish, and relatively little came from the anterior musculature. In addition, the contractile properties of the muscle along the length of the fish are significantly adapted to enhance power generation.

The influence of temperature on power output of scup red muscle during cyclical length changes

To gain insight into how temperature affects locomotory performance, we measured power output of scup red muscle during oscillatory length changes at 10 degrees C and 20 degrees C. When we optimized work loop parameters, we found that maximum power was 27.9 W kg-1 at 20 degrees C and 12.8 W kg-1 at 10 degrees C, giving a Q10 of 2.29. Maximum power was generated at a higher oscillation frequency at 20 degrees C (5 Hz) than at 10 degrees C (2.5 Hz), and the Q10 for power output at a given oscillation frequency ranged from about 1 at 1 Hz to about 5 at 7.5 Hz. An analysis of the results in terms of crossbridge kinetics suggests that the higher power output at 20 degrees C is associated with both a higher Vmax (i.e. more power per cycling crossbridge) and faster activation and relaxation (i.e. a greater number of cycling crossbridges). To obtain a more realistic understanding of the functional importance of temperature effects on muscle, we imposed on isolated muscle in vivo length changes and oscillation frequencies (measured during previous experiments on swimming scup) and the in vivo stimulus duty cycle (measured from electromyograms in this study). At 20 degrees C, muscle bundles tested under these in vivo conditions produced nearly maximal power, suggesting that the muscle works optimally during locomotion and, thus, important contractile parameters have been adjusted to produce maximum mechanical power at the oscillation frequencies and length changes needed during swimming. At 10 degrees C, muscle bundles tested under in vivo conditions produced much less power than was obtained during the ‘optimized’ work loop experiments discussed above. Furthermore, although ‘optimized’ work loop experiments showed that maximum power output occurs at 2.5 Hz, scup do not appear to swim with such a low tailbeat frequency. Although the reason for these apparent discrepancies at 10 degrees C are not known, it shows that simple extrapolation from isolated muscle to the whole animal, without knowledge of how the muscle is actually used in vivo, can be misleading.

Expression of dipeptidyl peptidase IV in rat tissues is mainly regulated at the mRNA levels

Dipeptidyl peptidase IV (DPPIV) is a serine peptidase that cleaves N-terminal dipeptides from polypeptides when the second residue is a proline or an alanine. We have recently cloned cDNAs for rat gp110, a membrane glycoprotein with Mr of 110,000 isolated initially from rat liver. Studies reported here establish that the gp110 for which we have cloned cDNAs is DPPIV. Using the antibodies against and cDNA for DPPIV, we have assessed the tissue distribution of DPPIV by molecular approaches. Immunoblot analysis demonstrated that DPPIV is present in the kidney, lung, and small intestine at high levels, in the liver and spleen at moderate levels, and in the heart at low levels. The highest levels of mRNA for DPPIV were detected in the kidney and small intestine as compared to moderate levels found in the lung, liver, and spleen. The lowest levels of DPPIV mRNA were found in the stomach, testis, and heart. No detectable DPPIV protein and mRNA were found in brain or muscle. LDPPIV protein and mRNA are present at much lower levels in fetal livers as compared to the adult liver. Indirect immunofluorescence microscopy demonstrated that DPPIV is localized in the bile canaliculus of hematocytes and in the apical membrane domains of kidney tubule and small intestine. Further studies by Southern blot analysis indicate that DPPIV is encoded by a single gene.