Characterization of Ca 2+ transport and enzyme activity in microsomes isolated from guinea-pig stomach smooth muscle

Abstract

1. 1. Ca 2+ uptake by microsomes prepared from guinea-pig stomach required the presence of both ATP and Mg 2+ and was unaffected by NaN 3. 2. 2. ATP-dependent Ca 2+ uptake increased with increasing free Ca 2+ concentration from 0.1 to 5μM and further increase in Ca 2+ concentration above 5μM did not enhance the uptake further. Half-saturation occurred at approximately 0.55μM. 3. 3. The t 1 2 values of Ca 2+ loss from these vesicles loaded in the presence of oxalate were significantly slower than those in the absence of oxalate. 4. 4. Enzyme activity suggested linkage between Ca 2+ uptake and ATPase activity and most of the azide-sensitive component of ATP hydrolysis was attributable to potent inhibition of ADPase activity.