“…A23187, as a Ca2+ionophore [Pressman, 1976;Rosen berger and Triggle, 1978] prevents energydependent Ca2+ transport by destroying the Ca2+ concentration gradient across the mem brane vesicles and has no effect on Ca2+ bind ing [Kwan et al, 1979a, Scarpa et al, 1972, Inorganic phosphate, which forms precipitat ing complex with Ca2+ inside the membrane vesicles, enhances active Ca2+ transport [Godfraind 1 1 al., 1976;Batra, 1978;Kutsky and Goodman, 1978]. Hypotonic shock, when applied to the closed membrane vesi cles pre-loaded with Ca2+ causes swelling and bursting of membrane vesicles, and thus re lease of free Ca2+ being transported [Grover et al, 1980], Since we have not compared the sidedness of these types of vesicles, we must admit the possibility that our results could be explained by a lower proportion of insideout, non-leaking plasma membrane.…”