What Does Maurocalcine Tell Us About the Process of Excitation-Contraction Coupling?

Abstract

IntroductionCardiac and skeletal muscle contraction is triggered by the arrival of an action potential that locally and transiently depolarizes the plasma membrane. The entire chain of molecular events that link the arrival of the action potential and muscle contraction is called excitation-contraction coupling. This chapter will focus on the way membrane depolarization is sensed and how it triggers a massive increase in the cytosolic Ca 2+ c o n c e n t r a t i o n . P l a s m a m e m b r a n e d e p o l a r i z a t i o n i s d e t e c t e d b y L -t y p e v o l t a g e -g a t e d calcium channels whose activation allows Ca 2+ entry into muscle cells. Cardiac and skeletal muscle voltage-gated calcium channels differ by their Ca 2+ permeability. While cardiac channels lead to an important and rapid Ca 2+ influx, skeletal muscle channel activation allows a moderate and rather slow Ca 2+ entry (Bean, 1989). In fact, the molecular identity of the pore-forming channel subunit differs in both tissues, cardiac fibers expressing the Ca v 1.2 isoform while skeletal muscles express the Ca v 1.1 isoform. Nevertheless, the overall subunit composition of both channels, illustrated in Figure 1, bears interesting similarities.