INFLUENCE OF AGE ON 1,25(OH)(2)-VITAMIN-D-3 ACTIVATION OF PROTEIN-KINASE-C IN RAT DUODENUM

We have studied age-related changes in the non-genomic regulation of p rotein kinase C (PKC) by 1,25-dihydroxy-vitamin D-3 [1,25(OH)(2)D-3] a nd their role in 1,25(OH)(2)D-3-dependent calcium uptake in the rat du odenum. Treatment of duodenal mucosae from 3 month-old (young) rats wi th hormone physiological concentrations (0.1 nM) induced an acute and transient stimulation of total tissue PKC activity which was maximal a t 1 min (+ 80%). The responses were evidenced up to 10 nM 1,25(OH)(2)D -3. The duodenum from 22 to 24 month old (aged) rats exhibited higher basal PKC activity which was not significantly modified after addition of the hormone. In the young duodenum PKC activation by 1,25(OH)(2)D- 3 was dependent on extracellular Ca2+ influx as it could be abolished to a great extent by EGTA and the Ca2+ channel blocker verapamil. In a ddition, the Ca2+ ionophore A23187 elicited a marked stimulation of du odenal mucosae PKC in young rats but was without effects in aged anima ls. 1,25(OH),D, increased the influx of Ca-45(2+) duodenal mucosae of young rats in a dose-(0.1-1 nM) and time-(1-10 min) dependent fashion. This response to the hormone was impaired in aged animals. Similarly as 1,25(OH)(2)D-3, the PKC activator dioctanoylglycerol (DOG) rapidly (1-5 min) increased [Ca-45(2+)] influx in duodena From young rats wher eas the response to DOG was blunted in senescent animals. Furthermore, PKC inhibitors (bisindolylmaleimide, staurosporine and compound H7) a bolished 1,25(OH),D, stimulation of Ca2+ uptake in the young duodenum. These results suggest that 1,25(OH)(2)D-3 regulates PKC activity in t he mammalian duodenum by a non-genomic mechanism which involves the ra pid influx of extracellular Ca2+, and that activation of PKC, in turn, mediates hormone stimulation of intestinal Ca2+ uptake. The data also indicates that 1,25(OH)(2)D-3 regulation of Ca2+ transport through th e PKC messenger system is impaired with aging. (C) 1997 Elsevier Scien ce Ireland Ltd.