Fig. 2.

Increase in basal phosphorylation of α₁1.2 on serine 1928 in 26-month-old rats. α₁1.2 was immunoprecipitated from hippocampal extracts of 12- and 26-month-old Lobund-Wistar rats. Immunoblots were probed with anti-CH1923-1932P, stripped with SDS and DTT, and reprobed with anti-CNC1 (26). Immunosignals for long- and short-form anti-CH1923-1932P (Top) and anti-CNC1 (Middle) were quantified by densitometry. Signals for anti-CH1923-1932P corrected for differences in relative amounts of α_1C based on the CNC1 signals of the long-form α_1C (Bottom). Values for long- and short-form α₁1.2 were normalized by setting the average values for long- and short-form α₁1.2 in adults as 100%. The average phosphorylation level of serine 1928 is 16.7% in adult rats (see Fig. 3); therefore, we set the average of all values for adult rats from each aging experiment equal to 16.7% and normalized all measured values accordingly. Bars represent average of 16 samples ± SEM. The small decrease in total amount of short-form α₁1.2 in old rats to 89 ± 6% of adult is statistically significant (P < 0.05 by one-way ANOVA and Dunnett's multiple comparison test).