Increased [3H]nitrendipine binding sites in rat heart during adult maturation and aging.
To study the effects of maturation and aging on calcium channels, we investigated the characteristics of binding of a radioligand, [3H]nitrendipine, to relatively pure sarcolemmal membranes from 2-, 12- and 24-month-old Sprague-Dawley rat hearts. Specific binding of [3H]nitrendipine was saturable, and the Scatchard analysis of the binding revealed a single class of binding sites. Binding of [3H]nitrendipine to the membrane of 12-month-old-rats was 50-75% greater than to the membrane of 2-month-old young adult rats with no further changes in binding during aging from 12 to 24 months. The maximum number of dihydropyridine binding sites (Bmax) was 70% higher in 12- and 24-month-old rat hearts (0.45 and 0.43 pmol/mg protein) than in 2-month-old rats (0.27 pmol/mg protein). The affinity for [3H]nitrendipine binding, on the other hand, was similar in all three age groups (KD values of 0.27, 0.31 and 0.29 nM in 2-, 12- and 24-month-old rats, respectively, at 25 degrees). Membranes of all three age groups showed a similar degree of enrichment in sarcolemmal marker enzymes, indicating that the difference in membrane purity was not a contributing factor to the observed increase in density. Furthermore, increased binding of [3H]nitrendipine to the membranes of older rat hearts was observed throughout the purification scheme. Since [3H]nitrendipine binding sites are considered to be specific sites for voltage-gated Ca2+ channels of the sarcolemma, it is concluded that the density of these channels in the myocardium increases during adult maturation and is maintained through senescence.
Navaratnam
S
S
Department of Internal Medicine, University of Manitoba, Winnipeg, Canada.
Khatter
J C
JC
D000367:Age Factors; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009568:Nitrendipine / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012508:Sarcolemma / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis
D015220:Calcium Channels; D009568:Nitrendipine; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium