In some species of fish, males contract and relax muscles which surround the gas-filled swimbladder at 100 Hz and up to 250 Hz to produce a mating call. Calcium (Ca2+), the switch for muscle contraction, is released from and pumped back into the sarcoplasmic reticuluum on each stimulus. The rapid contractions would seem to require a prodigious Ca2+ pumping rate. However the Ca2+ pumps are not very fast. Toadfish solve the Ca2+ problem in two ways: (1) Toadfish reduce the amount of Ca2+ released per stimulus and thus require less pumping. (2) Toadfish do not call continuously, they make 400 ms calls followed by a long 5-15 second intercall interval (i.e., 3-8% duty cycle calls). Toadfish possess a protein, parvalbumin (Parv), in very high concentrations which binds 70-80% of the Ca2+ released during a call. Parv then releases the Ca2+ slowly during the long intercall interval and it is pumped back at a modest rate. Another fish species, the midshipman, make a 100% duty cycle call and a single call can last 1 hour. Without the intercall interval to unload Ca2+, Parv cannot be useful. Accordingly, midshipman have only 1/7 of the Parv as toadfish. This leaves the problem: how can midshipman call? This research project will examine how much Ca2+ is released per stimulus, how the Ca2+ level changes during calling, and whether midshipman possess a means of performing mechanical work with little release and reuptake of Ca2+-utilizing a mechanism (asynchronous contraction) observed in insects, but never before seen in vertebrate muscle. The work will utilize innovative energetic analyses, high speed intracellular Ca2+ and high speed mechanics/video techniques (20,000 frames/s) developed by the collaborators. Toadfish and midshipman share neural mechanisms with birds and mammals and thus this work will improve our understanding of how vocal communication evolved. Also, extreme function usually involves extreme modifications, and thus studies of these extreme muscles will reveal new mechanisms that are not visible in normal muscle. This project will include mentoring underrepresented minority undergraduates through a REU program at the MBL in Woods Hole. In addition 1 or 2 undergraduate students from the PI's physiology and advanced muscle/biomechanics class will be given the opportunity to work on the project in Philadelphia and Woods Hole.
