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 biologically active metabolite of vitamin D₃, 1,25-dihydroxycholecalciferol [1,25(OH)₂D₃], could influence the activities of rat colonic particle 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 activities. The results of these studies demonstrated that: 1) 1,25(OH)₂D₃, in a concentration-dependent manner, rapidly (within minutes) stimulated guanylate, but not adenylate cyclase activity; 2) preincubation of the cells with staurosporine, a protein kinase inhibitor, or U73122, an inhibitor of phosphoinositide-phospholipase C-dependent processes, blocked the increase in guanylate cyclase activity induced by 1,25(OH)₂D₃; and 3) 12-O-tetradecanoyl phorbol 13-acetate and 1,2-dioctanoyl-sn-glycerol, known activators of protein kinase C, also rapidly stimulated rat colonic particulate guanylate cyclase activity. Taken together, these results demonstrate that 1,25(OH)₂D₃ rapidly stimulates rat colonic particulate guanylate cyclase, at least in part, via a protein kinase C-dependent mechanism.