Expression of smooth muscle MyHC B in blood vessels of hypertrophied heart in experimentally hypertensive rats

REM Sleep Rebound as an Adaptive Response to Stressful Situations

Stress and sleep are related to each other in a bidirectional way. If on one hand poor or inadequate sleep exacerbates emotional, behavioral, and stress-related responses, on the other hand acute stress induces sleep rebound, most likely as a way to cope with the adverse stimuli. Chronic, as opposed to acute, stress impairs sleep and has been claimed to be one of the triggering factors of emotional-related sleep disorders, such as insomnia, depressive- and anxiety-disorders. These outcomes are dependent on individual psychobiological characteristics, conferring even more complexity to the stress-sleep relationship. Its neurobiology has only recently begun to be explored, through animal models, which are also valuable for the development of potential therapeutic agents and preventive actions. This review seeks to present data on the effects of stress on sleep and the different approaches used to study this relationship as well as possible neurobiological underpinnings and mechanisms involved. The results of numerous studies in humans and animals indicate that increased sleep, especially the rapid eye movement phase, following a stressful situation is an important adaptive behavior for recovery. However, this endogenous advantage appears to be impaired in human beings and rodent strains that exhibit high levels of anxiety and anxiety-like behavior.

Smooth muscle molecular mechanics in airway hyperresponsiveness and asthma

Asthma is a respiratory disorder characterized by airway inflammation and hyperresponsiveness associated with reversible airway obstruction. The relative contributions of airway hyperresponsiveness and inflammation are still debated, but ultimately, airway narrowing mediated by airway smooth muscle contraction is the final pathway to asthma. Considerable effort has been devoted towards identifying the factors that lead to the airway smooth muscle hypercontractility observed in asthma, and this will be the focus of this review. Airway remodeling has been observed in severe and fatal asthma. However, it is unclear whether remodeling plays a protective role or worsens airway responsiveness. Smooth muscle plasticity is a mechanism likely implicated in asthma, whereby contractile filament rearrangements lead to maximal force production, independent of muscle length. Increased smooth muscle rate of shortening via altered signaling pathways or altered contractile protein expression has been demonstrated in asthma and in numerous models of airway hyperresponsiveness. Increased rate of shortening is implicated in counteracting the relaxing effect of tidal breathing and deep inspirations, thereby creating a contracted airway smooth muscle steady-state. Further studies are therefore required to understand the numerous mechanisms leading to the airway hyperresponsiveness observed in asthma as well as their multiple interactions.

(+)Insert smooth muscle myosin heavy chain (SM-B): From single molecule to human

In smooth muscle, alternative mRNA splicing of a single gene produces four myosin heavy chain (SMMHC) isoforms. Two of these isoforms differ by the presence [(+)insert] or absence [(-)insert] of a seven amino acid insert in the motor domain. This insert enhances the kinetic properties of myosin at the molecular level but its exact role at the cell and tissue levels still has to be elucidated. This review focuses on the expression and biological functions of the (+)insert isoform. Current knowledge is summarized regarding its tissue distribution in animals and humans. Studies at the molecular, cellular and tissue levels that aimed at understanding the contribution of this isoform to smooth muscle mechanical function are presented with a particular focus on velocity of shortening. In addition, the altered expression of the (+)insert isoform in diseases and models of diseases and the compensatory mechanisms that occur when the (+)insert is knocked out are discussed. The need for additional studies on the relationship of this isoform to contractile performance and how expression of this isoform is regulated are also considered.

Tuning smooth muscle contraction by molecular motors

As in striated muscle, smooth muscle cells (SMC) contract by Ca2+ activated cyclic interaction between actin and type II myosin. However, smooth muscle maintains tone at basal activating Ca2+ and low energetic cost during sustained activation. This review analyzes the regulation of phasic and tonic contraction of SMC on the molecular level. Type II myosin is the molecular motor also of smooth muscle contraction. Six myosin heavy chain (MHC) isoenzymes (four smooth muscle, two nonmuscle) and five myosin light chain (MLC) isoforms (two 17 kDa, two 20 kDa, one 23 kDa) are expressed in SMC. These myosin subunits could be generated by alternative splicing or by differential gene expression. Thus different myosin isoenzymes are generated which may be modified posttranslationally by phosphorylation, affecting the contractile state of the SMC. Furthermore, they may be part of distinct contractile systems which are targeted by different second messenger cascades and are recruited differentially during activation, electromechanical, and pharmacomechanical coupling. Low energy consumption, shortening velocity, and MLC20 phosphorylation at low Ca2+ activation levels during tone maintenance ("latch") could be explained by a switch from smooth muscle myosin to nonmuscle myosin activation upon prolonged activation.