Author Correction: Rubber bands reduce the cost of carrying loads.

In this Brief Communication, the scale bar in Fig. 2a should be '0.1 m' rather than '0.

Small Ca releases enable hour-long high-frequency contractions in midshipman swimbladder muscle.

Type I males of the Pacific midshipman fish () vibrate their swimbladder to generate mating calls, or "hums," that attract females to their nests. In contrast to the intermittent calls produced by male Atlantic toadfish (), which occur with a duty cycle (calling time divided by total time) of only 3-8%, midshipman can call continuously for up to an hour. With 100% duty cycles and frequencies of 50-100 Hz (15°C), the superfast muscle fibers that surround the midshipman swimbladder may contract and relax as many as 360,000 times in 1 h.

Intracellular calcium movements during relaxation and recovery of superfast muscle fibers of the toadfish swimbladder.

The mating call of the Atlantic toadfish is generated by bursts of high-frequency twitches of the superfast twitch fibers that surround the swimbladder. At 16°C, a calling period can last several hours, with individual 80-100-Hz calls lasting ∼ 500 ms interleaved with silent periods (intercall intervals) lasting ∼ 10 s. To understand the intracellular movements of Ca(2+) during the intercall intervals, superfast fibers were microinjected with fluo-4, a high-affinity fluorescent Ca(2+) indicator, and stimulated by trains of 40 action potentials at 83 Hz, which mimics fiber activity during calling.

Vocal production complexity correlates with neural instructions in the oyster toadfish (Opsanus tau).

Sound communication is fundamental to many social interactions and essential to courtship and agonistic behaviours in many vertebrates. The swimbladder and associated muscles in batrachoidid fishes (midshipman and toadfish) is a unique vertebrate sound production system, wherein fundamental frequencies are determined directly by the firing rate of a vocal-acoustic neural network that drives the contraction frequency of superfast swimbladder muscles. The oyster toadfish boatwhistle call starts with an irregular sound waveform that could be an emergent property of the peripheral nonlinear sound-producing system or reflect complex encoding in the central nervous system.

Optimized ratiometric calcium sensors for functional in vivo imaging of neurons and T lymphocytes.

The quality of genetically encoded calcium indicators (GECIs) has improved dramatically in recent years, but high-performing ratiometric indicators are still rare. Here we describe a series of fluorescence resonance energy transfer (FRET)-based calcium biosensors with a reduced number of calcium binding sites per sensor. These 'Twitch' sensors are based on the C-terminal domain of Opsanus troponin C.

Paying the piper: the cost of Ca2+ pumping during the mating call of toadfish.

Superfast fibres of toadfish swimbladder muscle generate a series of superfast Ca(2+) transients, a necessity for high-frequency calling. How is this accomplished with a relatively low rate of Ca(2+) pumping by the sarcoplasmic reticulum (SR)? We hypothesized that there may not be complete Ca(2+) saturation and desaturation of the troponin Ca(2+) regulatory sites with each twitch during calling. To test this, we determined the number of regulatory sites by measuring the concentration of troponin C (TNC) molecules, 33.

A simple experimentally based model using proprioceptive regulation of motor primitives captures adjusted trajectory formation in spinal frogs.

Spinal circuits may organize trajectories using pattern generators and synergies. In frogs, prior work supports fixed-duration pulses of fixed composition synergies, forming primitives. In wiping behaviors, spinal frogs adjust their motor activity according to the starting limb position and generate fairly straight and accurate isochronous trajectories across the workspace.

Is high concentration of parvalbumin a requirement for superfast relaxation?

It is generally thought that the rapid relaxation of fast muscles is facilitated by the Ca(2+) binding protein parvalbumin (Parv). Indeed superfast swimbladder (SWB) muscle of toadfish contains the largest concentration of this protein ever observed (up to 1.5 mM).

Superfast vocal muscles control song production in songbirds.

Birdsong is a widely used model for vocal learning and human speech, which exhibits high temporal and acoustic diversity. Rapid acoustic modulations are thought to arise from the vocal organ, the syrinx, by passive interactions between the two independent sound generators or intrinsic nonlinear dynamics of sound generating structures. Additionally, direct neuromuscular control could produce such rapid and precisely timed acoustic features if syringeal muscles exhibit rare superfast muscle contractile kinetics.

Controlling the freezing process: a robotic device for rapidly freezing biological tissues with millisecond time resolution.

A robotic cryogenic device was developed which allows freezing of thick biological tissues with millisecond time resolution. The device consists of two horizontally oriented hammers (pre-cooled with liquid N(2)) driven by two linear servo-motors. The tissue sample is bathed in Ringers contained in a chamber which drops rapidly out of the way just as the hammers approach.

The effect of temperature and thermal acclimation on the sustainable performance of swimming scup.

There is a significant reduction in overall maximum power output of muscle at low temperatures due to reduced steady-state (i.e. maximum activation) power-generating capabilities of muscle.

Biomechanics: rubber bands reduce the cost of carrying loads.

Vertical movement of the hip during locomotion causes a loaded backpack to be accelerated with each step, which imposes large peak forces on the wearer. Here we show that using bungee cords to suspend the load from a backpack frame reduces not only its vertical movement, and hence its vertical force on the carrier, but also the energetic cost of walking with the pack. This permits larger loads to be carried while moving rapidly, and at the same time reduces the risk of orthopaedic and muscular injury.

Design and function of superfast muscles: new insights into the physiology of skeletal muscle.

Superfast muscles of vertebrates power sound production. The fastest, the swimbladder muscle of toadfish, generates mechanical power at frequencies in excess of 200 Hz. To operate at these frequencies, the speed of relaxation has had to increase approximately 50-fold.

Generating electricity while walking with loads.

We have developed the suspended-load backpack, which converts mechanical energy from the vertical movement of carried loads (weighing 20 to 38 kilograms) to electricity during normal walking [generating up to 7.4 watts, or a 300-fold increase over previous shoe devices (20 milliwatts)]. Unexpectedly, little extra metabolic energy (as compared to that expended carrying a rigid backpack) is required during electricity generation.

Effect of chronic obstructive pulmonary disease on calcium pump ATPase expression in human diaphragm.

We have previously demonstrated that human diaphragm remodeling elicited by severe chronic obstructive pulmonary disease (COPD) is characterized by a fast-to-slow myosin heavy chain isoform transformation. To test the hypothesis that COPD-induced diaphragm remodeling also elicits a fast-to-slow isoform shift in the sarcoendoplasmic reticulum Ca(2+) ATPase (SERCA), the other major ATPase in skeletal muscle, we obtained intraoperative biopsies of the costal diaphragm from 10 severe COPD patients and 10 control subjects. We then used isoform-specific monoclonal antibodies to characterize diaphragm fibers with respect to the expression of SERCA isoforms.

Human diaphragm remodeling associated with chronic obstructive pulmonary disease: clinical implications.

Diaphragm remodeling associated with chronic obstructive pulmonary disease (COPD) consists of a fast-to-slow fiber type transformation as well as adaptations within each fiber type. To try to explain disparate findings in the literature regarding the relationship between fiber type proportions and FEV1, we obtained costal diaphragm biopsies on 40 subjects whose FEV1 ranged from 118 to 16% of the predicted normal value. First, we noted that our exponential regression model indicated that changes in FEV1 can account for 72% of the variation in the proportion of Type I fibers.

Cross-bridge blocker BTS permits direct measurement of SR Ca2+ pump ATP utilization in toadfish swimbladder muscle fibers.

Because the major processes involved in muscle contraction require rapid utilization of ATP, measurement of ATP utilization can provide important insights into the mechanisms of contraction. It is necessary, however, to differentiate between the contribution made by cross-bridges and that of the sarcoplasmic reticulum (SR) Ca2+ pumps. Specific and potent SR Ca2+ pump blockers have been used in skinned fibers to permit direct measurement of cross-bridge ATP utilization.

The design of vertebrate muscular systems: comparative and integrative approaches.

For more than 50 years, it has been known that vertebrates engage in a wide range of motor activities and that they possess muscle types with a similarly large range of contractile properties. However, only during the past 15 years has it been shown experimentally that the contractile properties of muscle fibers are well adjusted to their in vivo function. Arriving at this conclusion has required an integrative approach, that is, comparing measurements of muscle fiber properties with measurements of fiber use during normal motor activity.

Functional morphology of proximal hindlimb muscles in the frog Rana pipiens.

Musculoskeletal models have become important tools in understanding motor control issues ranging from how muscles power movement to how sensory feedback supports movements. In the present study, we developed the initial musculotendon subsystem of a realistic model of the frog Rana pipiens. We measured the anatomical properties of 13 proximal muscles in the frog hindlimb and incorporated these measurements into a set of musculotendon actuators.

Jumping in frogs: assessing the design of the skeletal system by anatomically realistic modeling and forward dynamic simulation.

Comparative musculoskeletal modeling represents a tool to understand better how motor system parameters are fine-tuned for specific behaviors. Frog jumping is a behavior in which the physical properties of the body and musculotendon actuators may have evolved specifically to extend the limits of performance. Little is known about how the joints of the frog contribute to and limit jumping performance.

The Quest for Speed: Muscles Built for High-Frequency Contractions.

Vertebrate sound-producing muscles can contract at frequencies greater than 100 Hz, a feat impossible in locomotory muscles. This is not accomplished by unique proteins or structures but by qualitative shifts in isoforms and quantitative reapportionment of structures. Speed comes with costs and trade-offs, however, that restrict how a muscle can be used.