Key result
Photoaffinity labeling with [3H]nitrendipine and ultraviolet irradiation identified a 32,000-Da protein in canine cardiac sarcoplasmic reticulum as the high affinity nitrendipine-binding site.
A 32,000-Da protein in the ryanodine-sensitive fraction of canine cardiac sarcoplasmic reticulum was identified as the high affinity nitrendipine-binding site.
Should not change clinical practice; leaves open the protein's functional role in cardiac calcium handling.
[3H]Nitrendipine and high intensity ultraviolet irradiation have been used to photoaffinity label the protein component of the high affinity nitrendipine-binding site in subcellular membrane fractions from canine cardiac muscle. Irradiation of isolated cardiac membranes in the presence of [3H]nitrendipine resulted in the covalent labeling of a protein component that migrated on sodium dodecyl sulfate-polyacrylamide gels with an apparent molecular weight of 32,000. Incorporation of [3H]nitrendipine did not occur in the absence of irradiation. The photoaffinity labeling of the 32,000-Da protein by [3H]nitrendipine was inhibited by excess unlabeled nitrendipine, nifedipine, or verapamil. EDTA, ATP, and La3+, which are known to reduce high affinity nitrendipine binding, also inhibited the photoaffinity labeling of this membrane protein by [3H]nitrendipine. The 32,000-Da [3H]nitrendipine-labeled protein was found to be enriched in the ryanodine-sensitive fraction of cardiac sarcoplasmic reticulum and absent from the ryanodine-insensitive fraction of cardiac sarcoplasmic reticulum which is known to lack high affinity nitrendipine binding. Therefore, the 32,000-Da photoaffinity-labeled [3H]nitrendipine-binding protein exhibits properties identical to those expected for the protein component of the high affinity nitrendipine-binding site in isolated cardiac membranes.
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Campbell et al. (1984) studied this question. [3H]Nitrendipine and high intensity ultraviolet irradiation vs. Absence of irradiation or presence of unlabeled competitors was evaluated on Photoaffinity labeling of the protein component of the high affinity nitrendipine-binding site. Photoaffinity labeling with [3H]nitrendipine and ultraviolet irradiation identified a 32,000-Da protein in canine cardiac sarcoplasmic reticulum as the high affinity nitrendipine-binding site.
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