Dihydropyridine and phenylalkylamine receptors associated with cardiac and skeletal muscle calcium channels are structurally different.
We have purified putative L-type Ca2+ channels from chick heart by virtue of their associated high affinity receptors for the Ca2+ channel effectors, dihydropyridines (DHPs), and phenylalkylamines (PAAs). A peptide of 185,000-190,000 daltons was found to comigrate with the peak of DHP binding activity during purification through two successive cycles of lectin affinity chromatography and sucrose density gradient centrifugation. A previously described peptide of 140,000 daltons, whose Mr was increased to approximately 180,000 under nonreducing conditions, also copurified with the 185-kDa peptide and dihydropyridine binding activity. When cardiac membranes were photolabeled with either the dihydropyridine [3H]azidopine or the PAA [3H]azidopamil prior to purification, a single, specifically labeled component of 185,000-190,000 daltons was present in the purified fractions. The properties of this 185-kDa cardiac DHP/PAA receptor were compared to the smaller 165-kDa DHP/PAA receptor previously purified from skeletal muscle. Antibodies raised against the 165-kDa skeletal muscle DHP/PAA receptor reacted with both rabbit and chick skeletal muscle receptors, but only poorly recognized, if at all, the cardiac 185-190 kDa component. The 185-kDa peptide present in the purified fractions obtained from cardiac muscle did not undergo substantial phosphorylation by cAMP-dependent protein kinase, while the purified 165-kDa peptide from rabbit and chick skeletal muscle was a good substrate for this kinase. The results show that the DHP and PAA receptors in cardiac muscle are contained in a 185-190-kDa peptide that is significantly larger than, and structurally and immunologically different from, it skeletal muscle counterpart.
Chang
F C
FC
Department of Biological Chemistry and Structure, University of Health Sciences, Chicago Medical School, Illinois 60064.
Hosey
M M
MM
D000345:Affinity Labels / Q000378:metabolism; D000818:Animals; D000906:Antibodies; D015220:Calcium Channels / Q000378:metabolism*; D002645:Chickens; D003459:Crystallins / Q000032:analysis*; D008566:Membranes / Q000378:metabolism; D008970:Molecular Weight; D009132:Muscles / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010777:Photochemistry; D011494:Protein Kinases / Q000378:metabolism; D011817:Rabbits; D011978:Receptors, Nicotinic / Q000378:metabolism*
D000345:Affinity Labels; D000906:Antibodies; D015220:Calcium Channels; D003459:Crystallins; D011978:Receptors, Nicotinic; D011494:Protein Kinases