Figure 110

Cellular mechanisms of vascular smooth muscle contraction. The vascular resistances of different arteriolar segments are ultimately regulated by the contractile tone of the corresponding vascular smooth muscle cells. Shown are the various membrane activation mechanisms and signal transduction events leading to a change in cytosolic calcium ions (Ca2+), cyclic AMP (cAMP), and phosphorylation of myosin light chain kinase. Many of the circulating hormones and paracrine factors that increase or decrease vascular smooth muscle tone are identified. Ad Cy—adenylate cyclase; ANP—atrial natriuretic protein; Cal—calmodulin; cGMP—cyclic GMP; DAG—1,2-diacylglycerol; Gq, Gj, Gs—G proteins; IP3—inositol 1,4,5-triphosphate; MLC—myosin light chain; MLCK—myosin light chain kinase; PGE2—prostaglandin E2; PGI2—prostaglandin I2; PKA—protein kinase A; PKC—protein kinase C; PLC—phospholipase C; PTH—parathyroid hormone; R—receptor; SR—sarcoplasmic reticulum; TXA2 — thromboxane A2. (Adapted from Navar et al. [16].)

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