Influences of NREM sleep on the activity of tonic vs. inspiratory phasic muscles in normal men.

Studies of sleep influences on human pharyngeal and other respiratory muscles suggest that the activity of these muscles may be affected by non-rapid-eye-movement (NREM) sleep in a nonuniform manner. This variable sleep response may relate to the pattern of activation of the muscle (inspiratory phasic vs. tonic) and peripheral events occurring in the airway. Furthermore, the ability of these muscles to respond to respiratory stimuli during NREM sleep may also differ. To systematically investigate the effect of NREM sleep on respiratory muscle activity, we studied two tonic muscles [tensor palatini (TP), masseter (M)] and two inspiratory phasic ones [genioglossus (GG), diaphragm (D)], also measuring the response of these muscles to inspiratory resistive loading (12 cmH2O.l-1.s) during wakefulness and NREM sleep. Seven normal male subjects were studied on a single night with intramuscular electrodes placed in the TP and GG and surface electrodes placed over the D and M. Sleep stage, inspiratory airflow, and moving time average electromyograph (EMG) of the above four muscles were continuously recorded. The EMG of both tonic muscles fell significantly (P less than 0.05) during NREM sleep [TP awake, 4.3 +/- 0.05 (SE) arbitrary units, stage 2, 1.1 +/- 0.2; stage 3/4, 1.0 +/- 0.2. Masseter awake, 4.8 +/- 0.6; stage 2, 3.3 +/- 0.5; stage 3/4, 3.1 +/- 0.5]. On the other hand, the peak phasic EMG of both inspiratory phasic muscles (GG and D) was well maintained.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in calmodulin and calmodulin-binding proteins in phasic and tonic smooth muscles

To determine whether densities ofcalmodulin (CaM) and CaM-binding proteins are related to phasic andtonic behavior of smooth muscles, we quantified these proteins in theopossum esophageal body (EB) and lower esophageal sphincter (LES),which represent phasic and tonic smooth muscles, respectively. Gelelectrophoresis, immunoprecipitation, Western blot, and hemagglutininepitope-tagged CaM (HA-CaM) overlay assay with quantitative scanningdensitometry and phosphorylation measurements were used. Total proteincontent in the two smooth muscles was similar (~30 mg protein/gfrozen tissue). Total tissue concentration of CaM was significantly(25%) higher in EB than in LES (P < 0.05).HA-CaM-binding proteins were qualitatively similar in LES and EBextracts. Myosin, myristoylated alanine-rich C kinase substrateprotein, Ca²⁺/CaM kinase II, and calponin contents werealso similar in the two muscles. However, content and total activity ofmyosin light chain kinase (MLCK) and content of caldesmon (CaD) werethree- to fourfold higher in EB than in LES. Increased CaM and MLCKcontent may allow for a wide range of contractile force varying fromcomplete relaxation in the basal state to a large-amplitude,high-velocity contraction in EB phasic muscle. Increased content ofCaD, which provides a braking mechanism on contraction, may furthercontribute to the phasic contractile behavior. In contrast, low CaM,MLCK, and CaD content may be responsible for a small range ofcontractile force seen in tonic muscle of LES.

     

Increased autophagy in chloroquine-treated tonic and phasic muscles: An alternative view

Ultrastructural and cytochemical techniques were used to investigate autophagy in the tonic anterior (ALD) and phasic posterior (PLD) latissimus dorsi muscles of the chicken following chloroquine administration. Autophagic vacuoles were seen in the ALD after 1 day of chloroquine administration while no change was seen in the PLD until 3 days. In both muscles, autophagic vacuoles and myeloid bodies were found at the level of the I band. Myeloid bodies usually were found in the longitudinal rows of mitochondria in the ALD muscle. Some, but not all, of the autophagic vacuoles and myeloid bodies were cytochemically acid phosphatase positive, while the portion of the sarcoplasmic reticulum of both muscles which is normally acid phosphatase positive was devoid of activity following chloroquine administration. These observations are discussed in regard to accepted mechanisms of autophagy and the possible inhibition of autophagy in skeletal muscle tissue by chloroquine.     

Differences in contractile protein content and isoforms in phasic and tonic smooth muscles

The basis of tonic vs. phasic contractile phenotypes of visceralsmooth muscles is poorly understood. We used gel electrophoresis andquantitative scanning densitometry to measure the content and isoformcomposition of contractile proteins in opossum lower esophagealsphincter (LES), to represent tonic muscle, and circular muscle of theesophageal body (EB), to represent phasic smooth muscle. The amount ofprotein in these two types of muscles is similar: ~27 mg/g of frozentissue. There is no difference in the relative proportion of myosin,actin, calponin, and tropomyosin in the two muscle types. However, theEB contains ~2.4-times more caldesmon than the LES. The relativeratios of - to -contractile isoforms of actin are 0.9 in the LESand 0.3 in EB. The ratio between acidic (LC17a) and basic (LC17b)isoforms of the 17-kDa essential light chain of myosin is 0.7:1 in theLES, compared with 2.7:1 in the EB. There is no significant differencein the ratios of smooth muscle myosin SM1 and SM2 isoforms in the two muscle types. The level of the myosin heavy chain isoform, which contains the seven-amino acid insert in the myosin head, is about threefold higher in the EB compared with LES. In conclusion, the esophageal phasic muscle in contrast to the tonic LES contains proportionally more caldesmon, LC17a, and seven-amino acid-inserted myosin and proportionally less -actin. These differences may providea basis for functional differences between tonic and phasic smoothmuscles.

     

Extravascular localization of albumin and IgG in normal tonic and phasic muscles of the rat

Summary Interstitial space localizations of albumin and IgG by sensitive immunohistochemical methods have reaffirmed that many large molecular weight proteins exit the vascular system and pass into the interstitial spaces between skeletal muscle fibres. Extensor digitorum longus and soleus muscles were found to contain native albumin and IgG and perhaps other serum proteins such as complement C₃ or fibrinogen. In addition, IgG content was observed to increase with age but both the locale and apparent concentrations of the other molecules remained unchanged.     

The impact of state of bladder fullness on tonic and phasic activation of the pelvic floor muscles in women

PurposeWe aimed to determine if state of bladder fullness affects pelvic floor muscle activation in healthy women without urogenital symptoms.Materials and methodsTwenty-three nulliparous, continent female participants were recruited to participate. Women were randomized to begin the protocol with either an empty (EF) or a full (FE) bladder. Tonic and maximal voluntary pelvic floor muscle electromyographic activity were measured in three states of bladder fullness (empty, full and uncomfortably full). Electromyographic signal amplitudes were compared among bladder states using separate two-way repeated-measures analyses of variance including bladder state and test order as main effects as well as the interaction between bladder state and test order.ResultsTonic activity of the pelvic floor muscles was significantly higher in the full and uncomfortably full bladder states compared to when the bladder was empty (p < 0.005). Maximum voluntary electromyographic activation was unaffected by state of bladder fullness (p = 0.713).ConclusionsConsistent with studies in which the bladder was filled through saline infusion, these results suggest that tonic activity of the PFMs is higher when the bladder is full compared to when it is empty. However once the bladder is moderately full, tonic PFM activity does not increase with increases in bladder volume.     

Determinants of tonic and phasic reactions in transswitching

Forty-eight college students were assigned randomly to four groups in a 2 X 2 factorial arrangement of phasic conditional stimuli (same vs. different) and tonic conditional stimuli (same vs. different) to receive 2 days of classical conditioning with a transswitching procedure. Tonic stimuli were a 5-minute projected white triangle or circle; phasic stimuli were a 5-second red or green square superimposed over the tonic stimuli. There were six tonic stimulus segments each day, separated by 20-second periods of no stimulus, three containing six trials of the phasic stimulus paired with shock and three containing six trials of the phasic stimulus alone, in the counterbalanced order. Tonic responding at the onset of the tonic stimuli or during brief periods following its onset were recorded, along with phasic responses to the phasic stimuli. Responses included magnitude of skin conductance responses, frequency of unelicited skin conductance responses, and tonic heart rate. Both skin conductance measures of responding to the tonic stimuli differentiated significantly between positive and negative tonic segments during Day 2, but only in the group with two different tonic stimuli and one phasic stimulus ("standard" transswitching). This supported the hypothesis that tonic stimulus differentiation would be absent when two different phasic stimuli were present. The heart rate data did not support this hypothesis, showing tonic differentiation in both groups with two tonic stimuli. Phasic differentiation controlled by the different phasic stimuli was observed on Day 1; on Day 2, phasic differentiation was present only in the group with two tonic and one phasic stimuli and the group with one tonic and two phasic stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics of contraction initiated by flash photolysis of caged adenosine triphosphate in tonic and phasic smooth muscles

Laser flash photolysis of caged adenosine triphosphate (ATP), in the presence of Ca2+, was used to examine the time course of isometric force development from rigor states in glycerinated tonic (rabbit trachealis) and phasic (guinea-pig ileum and portal vein) smooth muscles. Photolytic liberation of ATP from caged ATP initiated force development, at 20 degrees C, with half-time (t1/2) of 5.4 s in trachealis and 1.2-2.2 s in the phasic muscles. Prior to photolysis, some muscles were phosphorylated with ATP plus okadaic acid (an inhibitor of myosin light-chain phosphatase) or thiophosphorylated with ATP gamma S to fully activate the regulatory system, before turning on the contractile apparatus. In these prephosphorylated muscles, force development, after caged ATP photolysis, was more rapid than in the unphosphorylated muscles, but the t1/2 values for trachealis (0.8-1.1 s) were still longer than for ileum and portal-vein muscles (0.20-0.25 s). The results suggest that both the contractile machinery and the regulatory system are slower in the tonic than in the phasic smooth muscles. The time course of force development for each muscle type was sigmoidal, with an initial delay (td) of approximately 10% of the t1/2 value. Some possible chemical and mechanical origins of the delay are discussed.     

Potential phasic and tonic muscles express a common set of fast and slow myosin light chains and fast tropomyosin during early development of chick embryo

We investigated the expression of myosin light chains and tropomyosin subunits during chick embryonic development of the anterior (ALD) and posterior (PLD) parts of the latissimus dorsi muscles. As early as day 8 in ovo, both muscles accumulate a common set of myosin light chains (LC) in similar ratios (LC1F : 55 per cent; LC2S : 25 per cent; LC2F : 12 per cent ; LC1S : 8 per cent) and a common set of tropomyosin (TM) subunits (β², β¹, α²_F).Later during development, the slow components of the LC regularly disappear in the PLD and the fast components of the LC and the α²_FTM disappear in the ALD, so that the adult pattern is almost established at the time of hatching.Thus, early in development, the two muscles accumulate a common set of fast and slow myosin light chains and fast tropomyosin and some isoforms are repressed at a later stage during development. These data might suggest that during development, the regulatory mechanisms of muscle specific isoform expression differ from one contractile protein to another.