Ciliary muscle is a smooth muscle characterized by a rapid response to muscarinic receptor stimulation and sustained contraction. Although it is evident that these contractions are Ca2+-dependent, detailed molecular mechanisms are still unknown. In order to elucidate the role of Ser/Thr protein phosphatase 2A (PP2A) in ciliary muscle contraction, we examined the effects of okadaic acid and othe...

During contractions, there is a net efflux of phosphate from skeletal muscle, likely because of an elevated intracellular inorganic phosphate (P(i)) concentration. Over time, contracting muscle could incur a substantial phosphate deficit unless P(i) uptake rates were increased during contractions. We used the perfused rat hindquarter preparation to assess [(32)P]P(i) uptake rates in muscles at ...

To gain insights into the physiological role of cotransmission, we measured peptide release from cell B15, a motorneuron that utilizes ACh as its primary transmitter but also contains putative peptide cotransmitters, the small cardioactive peptides (SCPs) and the buccalins (BUCs). All stimulation parameters used were in the range in which B15 fires in freely moving animals. We stimulated neuron...

exceeds that produced by the muscle, it will lengthen. Lengthening, or eccentric, muscle contractions have a surprisingly long history in physiological studies. (Note that this word was first introduced as “excentric” by Asmussen in 1953. This original spelling is more enlightening as it combines the prefix ex, “from or away,” with centric, “center,” hence a muscle contraction that is moving aw...

Sarcomerogenesis, or the addition of sarcomeres in series within a fiber, has a profound impact on the performance of a muscle by increasing its contractile velocity and power. Sarcomerogenesis may provide a beneficial adaptation to prevent injury when a muscle consistently works at long lengths, accounting for the repeated-bout effect. The association between eccentric exercise, sarcomerogenes...

Wigmore, D. M., B. M. Damon, D. M. Pober, and J. A. Kent-Braun. MRI measures of perfusion-related changes in human skeletal muscle during progressive contractions. J Appl Physiol 97: 2385–2394, 2004. First published August 6, 2004; doi:10.1152/ japplphysiol.01390.2003.—Although skeletal muscle perfusion is fundamental to proper muscle function, in vivo measurements are typically limited to thos...

exceeds that produced by the muscle, it will lengthen. Lengthening, or eccentric, muscle contractions have a surprisingly long history in physiological studies. (Note that this word was first introduced as “excentric” by Asmussen in 1953. This original spelling is more enlightening as it combines the prefix ex, “from or away,” with centric, “center,” hence a muscle contraction that is moving aw...

Intramuscular pressure (IMP) and electromyography (EMG) mirror muscle force in the nonfatigued muscle during static contractions. The present study explores whether the constant IMP-EMG relationship with increased force may be extended to dynamic contractions and to fatigued muscle. IMP and EMG were recorded from shoulder muscles in three sessions: 1). brief static arm abductions at angles from...

Electrical and contractile activities of smooth muscle strips isolated from the circular muscle layer of cat gastric antrum were studied using the sucrose gap technique. Bombesin (10(-8) mol/l) depolarized the gastric muscle; this was accompanied by an increase in the strip tone, in the plateau action potential frequency and in both the frequency and the amplitude of the spike potentials as wel...