Influence of age on 1,25(OH)2-vitamin D3 activation of protein kinase C in rat duodenum

We have studied age-related changes in the non-genomic regulation of protein kinase C (PKC) by 1,25-dihydroxy-vitamin D3 [1,25(OH)2D3] and their role in 1,25(OH)2D3-dependent calcium uptake in the rat duodenum. Treatment of duodenal mucosae from 3 month-old (young) rats with hormone physiological concentrations (0.1 nM) induced an acute and transient stimulation of total tissue PKC activity which was maximal at 1 min (+80%). The responses were evidenced up to 10 nM 1,25(OH)2D3. 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)2D3 was dependent on extracellular Ca2+ influx as it could be abolished to a great extent by EGTA and the Ca2+ channel blocker verapamil. In addition, the Ca2+ ionophore A23187 elicited a marked stimulation of duodenal mucosae PKC in young rats but was without effects in aged animals. 1,25(OH)2D3 increased the influx of 45Ca2+ in 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)2D3, the PKC activator dioctanoylglycerol (DOG) rapidly (1-5 min) increased [45Ca2+] influx in duodena from young rats whereas the response to DOG was blunted in senescent animals. Furthermore, PKC inhibitors (bisindolylmaleimide, staurosporine and compound H7) abolished 1,25(OH)2D3 stimulation of Ca2+ uptake in the young duodenum. These results suggest that 1,25(OH)2D3 regulates PKC activity in the mammalian duodenum by a non-genomic mechanism which involves the rapid 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)2D3 regulation of Ca2+ transport through the PKC messenger system is impaired with aging.