A personal historic perspective on the role of chloride in skeletal and cardiac muscle.

During the early decades of the last century, skeletal muscle was held to be impermeable to chloride ions. This theory, based on shaky grounds, was famously falsified by Boyle and Conway in 1941. Two decades later and onwards, the larger part of the resting conductance of skeletal muscle was found to be due to chloride ions, sensitive to the chemical environment, and to be time-and-voltage dependent. So, much of the groundwork for the physiological role of chloride ions in skeletal muscle was laid before the game-changing discovery of chloride channels. The early history of the role of chloride in cardiac muscle, and work on the relative permeability to foreign anions of different muscles are also here covered from a personal perspective.