1,25-DIHYDROXYCHOLECALCIFEROL RAPIDLY ACTIVATES RAT COLONIC PARTICULATE GUANYLATE-CYCLASE VIA A PROTEIN-KINASE C-DEPENDENT MECHANISM

The present studies were performed to determine whether the major biol ogically active metabolite of vitamin D3, 1,25-dihydroxycholecalcifero l [1,25(OH)2D3], could influence the activities of rat colonic particu late guanylate cyclase and adenylate cyclase. To address these issues, colonocytes were harvested from Sprague-Dawley rats and suspended in Krebs-Ringer bicarbonate buffer. The cells were then treated with 1,25 (OH)2D3 or other agents (see below) and crude membranes were prepared and analyzed for particulate guanylate cyclase and adenylate cyclase a ctivities. The results of these studies demonstrated that: 1) 1,25(OH) 2D3, in a concentration-dependent manner, rapidly (within minutes) sti mulated guanylate, but not adenylate cyclase activity; 2) preincubatio n of the cells with staurosporine, a protein kinase inhibitor, or U731 22, an inhibitor of phosphoinositide-phospholipase C-dependent process es, blocked the increase in guanylate cyclase activity induced by 1,25 (OH)2D3; and 3) 12-O-tetradecanoyl phorbol 13-acetate and 1,2-dioctano yl-sn-glycerol, known activators of protein kinase C, also rapidly sti mulated rat colonic particulate guanylate cyclase activity. Taken toge ther, these results demonstrate that 1,25(OH)2D3 rapidly stimulates ra t colonic particulate guanylate cyclase, at least in part, via a prote in kinase C-dependent mechanism.