PLASMA-MEMBRANE AND SARCOPLASMIC-RETICULUM CA-ATPASE AND SMOOTH-MUSCLE

Calcium ions (Ca2+) are involved in the regulation of many cellular ac tivities. The Ca-ATPase(s) of the plasma membrane and of the endoplasm ic reticulum play an important role in controlling the intracellular C a2+ concentration. Therefore, it is not unexpected that these enzymes are modulated by different factors. The activity of the plasma membran e Ca-ATPase is modified by the amount of negatively charged phospholip ids surrounding the enzyme. The regulation of the endoplasmic reticulu m Ca-ATPase depends on the phosphorylation of phospholamban by cAMP- a nd cGMP-dependent protein kinase. These two different Ca2+ transport A TPases are present in both visceral and vascular smooth muscle, but ti ssue- and species-dependent differences in their relative amount have been observed. In this article we will review the characteristics of C a-ATPases of the smooth muscle.