The ontogeny of [³H]nitrendipine binding sites and ⁴⁵Ca²⁺ uptake processes in brain synaptosomes from spontaneously hypertensive rats

Potassium-stimulated ⁴⁵Ca²⁺ uptake into rat brain cerebral cortex synaptosomes was measured in spontaneously hypertensive rats at ages two days to 140 days. The fast and slow phases of ⁴⁵Ca²⁺ uptake were measured. The slow phase was abolished by replacement of Na⁺ by choline, was more sensitive to 3,4-dichlorobenzamil and likely represents Na⁺:Ca²⁺ exchange. The fast and slow phases of ⁴⁵Ca²⁺ uptake developed at different rates, the slow phase developing more rapidly and being more prominent at younger ages, but both phases were at a maximum at 5 weeks. [³H]Nitrendipine binding increased from 2 days (B_max = 39 ± 1 fmol mg^-1 protein), without change in K_d (mean = 130 ± 7 × 10^-12 M). Development of [³H]nitrendipine binding paralleled that of the fast phase of ⁴⁵Ca²⁺ uptake. Neither ⁴⁵Ca²⁺ uptake (both phases) nor [³H]nitrendipine binding (B_max) changed between 5 weeks (prehypertensive) and 20 weeks (established hypertensive) of age.