Chapter 44 – Smooth Muscle Excitability

The resting membrane potential and excitability profiles of smooth muscle cells (SMCs) determine the patterns of contraction and relaxation in SMC-containing organs including the vasculature, the gastrointestinal tract and the respiratory system. The populations of ion channels are organ and site-specific and thereby uniquely situated to support the distinctly different physiological functions of each organ. This chapter has taken the liberty of focusing on the contribution of K + and Ca 2+ -conducting channels to SMC excitation–contraction coupling using vascular smooth muscle as an initial model. Subsequent sections emphasize that the SMCs of different organ systems express unique blueprints of ion channels, which are subjected to modulation by external stimuli including neurotransmitters, autocoids and other specialized input to determine the final level of smooth muscle tone.