ATP-dependent membrane-located calcium transport systems are widely distributed and activated by potassium ions

Abstract 1. 1. ATP-dependent calcium transport systems were identified in a variety of tissues of a number of animal species. 2. 2. Responses of the transport systems to changes in pH, calcium and magnesium ion concentrations suggest a common phylogenetic origin. 3. 3. Calcium pump activities were stimulated by potassium ions. 4. 4. The tissue-specific inhibition of the activities of the calcium pump by potassium ions in skeletal and heart muscle at low calcium concentrations may be responsible for muscle tone and basal muscle thermogenesis.