Chapter 46 - Cyclic Nucleotides and Protein Phosphorylation in Vascular Smooth Muscle Relaxation

Abstract

This chapter focuses on the relaxation of vascular smooth muscle, which involves reducing [Ca2+]i by increasing the efflux of this cation out of the cell, decreasing its influx, or increasing its intracellular sequestration. Additionally, the sensitivity of the contractile apparatus to Ca2+ may be decreased so that there is a decreased contractile response at any given intracellular concentration of Ca2+. Smooth muscle relaxation is mediated by the intracellular second messengers cyclic AMP and cyclic GMP. The production and metabolism of these cyclic nucleotides and the regulation of intracellular concentrations of Ca2+ are highly interdependent. Cyclic nucleotides mediate vascular smooth muscle relaxation by various mechanisms involving alterations in intracellular concentrations of Ca2+ or the sensitivity of the contractile apparatus to that cation. A complex relationship exists between the regulation of intracellular concentrations of cyclic nucleotides and Ca2+ and vascular smooth muscle contractility. This complexity is reflected in the precision with which the contractile tone of vascular smooth muscle regulates total peripheral resistance and regional blood flow to meet physiological requirements.