[Changes in muscarinic receptors on lymphocytes in normal aging and Alzheimer's disease]

It has been previously reported that responses of T-lymphocytes to stimulation by phytohemagglutinin declined as age advanced. However, it has not been demonstrated whether receptor binding capacity decreased with age. The potent muscarinic cholinergic antagonist, 3-quinuclidinyl benzilate (QNB) was used to detect the characterization of muscarinic acetylcholine receptors (mAChR) on human lymphocytes. Using techniques developed for the study of mAChR in brain homogenate, direct binding to whole live lymphocytes was shown for the [3H]-QNB. Three age groups of healthy female adults were examined: 42-49 (N = 7), 50-59 (N = 7) and 60-69 years old (N = 8). Moreover, we studied mAChR on lymphocytes from 11 patients (54-65 years old, female) with probable Alzheimer's Disease. Specific binding is saturable, proportional to cell concentration, and can be displaced by atropine. For control subjects (age range 42-69 years old, N = 22), a positive correlation (r = 0.634, alpha less than 0.01) was found between Kd and age. Also positive correlation between Bmax and age was shown to be strong (r = 0.434, alpha less than 0.05), The regression equations are: Y = 3.25X - 109.5 (Kd); Y = 24.7X - 201.8 (Bmax); where, X and Y designate the age of individuals and Kd (or Bmax), respectively. Hence, for patients with Alzheimer's Diseases, the correlation between Kd and age, and between Bmax and age, were weak (r = -0.352, 0.011, not significant, respectively). No significant change in Kd or Bmax was obtained on lymphocytes from patients, compared to age-matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)