NEW METHOD FOR MEASURING THE KINETICS OF TRANSMEMBRANE CA-45 EFFLUX IN THE SMOOTH-MUSCLE OF THE GUINEA-PIG TAENIAE-COLI

A simple technique has been developed for resolving cellular 45Ca efflux from intestinal smooth muscle into two exponential components. Strips of taenia coli from guinea pig are labeled with 45Ca for three hours and then washed in an ice-cold, oxygenated medium containing 5 mM CaEGTA and 1.5 mM excess Ca2+ for 40 minutes in order to remove extracellularly bound label. Tissues subsequently placed in a control physiological solution at 37°C exhibit an efflux profile of 45Ca which can be resolved into two exponential components. The apparent magnitudes and rate constants of these components are sensitive to ionic alterations of the medium and to biochemical manipulation of the Ca2+ compartmentalization within the cells. © 1979.