Intrinsic smooth muscle

The underlying intrinsic smooth muscle motility is modulated by neurohormonal influences. Afferent sensory neurons, extrinsic motor neurons, and intramural neurons innervate the gut. It also has mucosal sensory receptors for monitoring chemical, osmotic, or painful stimuli and muscle receptors to monitor degrees of stretch. 

The penis is mainly supplied by the internal pudendal artery, and three major sets of veins, superficial, intermediate, and deep veins, drain it. Drug-induced changes in neurotransmitter action can affect local blood flow. Vascular supply, intrinsic smooth muscles of the penis, and adjacent striated muscles are controlled by nerves arising from the thoracolumbar sympathetic, the lumbosacral parasympathetic, and the lumbosacral somatic systems. The pudendal nerve is the major somatic pathway innervating the male genitalia. 

Ignarro LJ, Byrns RE, Wood KS (1987) Endothelium-dependent modulation of cGMP levels and intrinsic smooth muscle tone in isolated bovine intrapulmonary artery and vein. Circ Res 60 82-92... 

P2X X CM CL Smooth muscle, platelets, cerebellum, dorsal horn spinal neurons a, 3-meATP = ATP = 2-MeSATP, L-p.y-meATP (rapid desensitization) TNP-ATP, lp5l, NF023, NF449 Intrinsic cation channel (Ca2+ and Na+)... 

P2X2 Smooth muscle, CNS, retina, chromaffin cells, autonomic and sensory ganglia ATP>ATPyS>2- MeSATP > > a,p-meATP (pH + zinc sensitive) Suramin, isoPPADS, RB2, NF770, NF279 Intrinsic ion channel (particularly Ca2+)... 

The general picture of muscle contraction in the heart resembles that of skeletal muscle. Cardiac muscle, like skeletal muscle, is striated and uses the actin-myosin-tropomyosin-troponin system described above. Unlike skeletal muscle, cardiac muscle exhibits intrinsic rhyth-micity, and individual myocytes communicate with each other because of its syncytial nature. The T tubular system is more developed in cardiac muscle, whereas the sarcoplasmic reticulum is less extensive and consequently the intracellular supply of Ca for contraction is less. Cardiac muscle thus relies on extracellular Ca for contraction if isolated cardiac muscle is deprived of Ca, it ceases to beat within approximately 1 minute, whereas skeletal muscle can continue to contract without an extraceUular source of Ca +. Cyclic AMP plays a more prominent role in cardiac than in skeletal muscle. It modulates intracellular levels of Ca through the activation of protein kinases these enzymes phosphorylate various transport proteins in the sarcolemma and sarcoplasmic reticulum and also in the troponin-tropomyosin regulatory complex, affecting intracellular levels of Ca or responses to it. There is a rough correlation between the phosphorylation of Tpl and the increased contraction of cardiac muscle induced by catecholamines. This may account for the inotropic effects (increased contractility) of P-adrenergic compounds on the heart. Some differences among skeletal, cardiac, and smooth muscle are summarized in... 

Paul That s probably where I would be coming down. The speed of a smooth muscle is not set by the Ca2+ release. I would maintain that the speed of the muscle is set by its intrinsic unloaded shortening velocity, as modulated by its elasticity and whatever force it is facing. Generally, the Ca2+ transient is largely over before the smooth muscle contracts. I don t believe that the speed of the smooth muscle is regulated by means of Ca2+ waves. 

Although previous studies suggested a basal tone of smooth muscle mediated by histamine binding to HRl, constitutive intrinsic activity of the HRl without any occupation by histamine might be more relevant. Histamine also induces proliferation of cultured airway smooth muscle cells [63]. 

According to current thinking, epithelial dysfunction, either intrinsic to asthma or caused by persistent inflammation, leads to epithelial release of profibrotic cytokines such as epidermal growth factor and TGF-P acting on fibroblasts and smooth muscle cells, disturbing the equilibrium... 

Because the p-receptors of the heart are primarily of the pi type and those in the pulmonary and vascular smooth muscle are p2 receptors, Pi-selective antagonists are frequently referred to as cardioselective blockers. The intrinsic activity, cardioselectivity, and membrane-stabilizing actions of a number of p-blockers are summarized in Table 11.2... 

The technical problems involved with any attempt to use analogously systematic research approaches to a potential transmitter in the central nervous system are great. Peripheral synapses can be isolated by microdissection, they can remain functional in an isolated profusion experimental situation for hours, and their activation can be manifested by clearly defined and measurable phenomena (such as the miniature end-plate potential or the contraction of smooth muscle). The central nervous system has little in the way of focal synaptic regions. The dendrites and the cell bodies of central neurons are densely covered with synapses, many of which may be of a chemically heterogenous nature. In addition, the extra-neuronal space is packed with a tangle of glia, closely approximating the membranous surfaces of nerve cells and possibly intrinsically important to their function. This makes the isolated, chemical manipulation of central synapses extremely difficult. (Mandell and Spooner 1968, p. 1443)... 

Resting tone reflects basal properties intrinsic to the smooth muscle cells and the modulahng influence of several well defined extrinsic factors [116]. These... 

---