Characterization of mammalian heart annexins with special reference to CaBP33 (annexin V)

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Abstract
Porcine heart was observed to express annexins V (CaBP33) and VI in large amounts, and annexins III and IV in much smaller amounts. Annexin V (CaBP33) in porcine heart was examined in detail by immunochemistry. Homogenization and further processing of heart in the presence of EGTA resulted in the recovery of annexin V (CaBP33) in the cytosolic fraction and in an EGTA‐resistant, Triton X‐100‐soluble fraction from cardiac membranes. Including Ca2+ in the homogenization medium resulted in a significant decrease in the annexin V (CaBP33) content of the cytosolic fraction with concomitant increase in the content of this protein in myofibrils, mitochrondria, the sarcoplasmic reticulum and the sarcolemma. The amount of annexin V (CaBP33) in each of these subfractions depended on the free Ca2+ concentration in the homogenizing medium. At the lowest free Ca2+ concentration tested, 0.8 μM, only the sarcolemma appeared to contain bound annexin V (CaBP33). Membrane‐bound annexins V (CaBP33) and VI partitioned in two fractions, one EGTA‐resistant and Triton X‐100‐extractable, and one Triton X‐100‐resistant and EGTA‐extractable. Altogether, these data suggest that annexins V and VI are involved in the regulation of membrane‐related processes.