Ca2(+)-channel agonist BAY K8644 mimics 1,25(OH)2-vitamin D3 rapid enhancement of Ca2+ transport in chick perfused duodenum.

To further understand the molecular mechanism by which 1,25(OH)2-vitamin D3 [1,25(OH2D3] rapidly stimulates intestinal calcium transport (termed "transcaltachia"), the effect of the calcium channel agonist BAY K8644 was studied in vascularly perfused duodenal loops from normal, vitamin D-replete chicks. BAY K8644, 2 mu M, was found to stimulate 45Ca2+ transport from the lumen to the vascular effluent to the same extent as physiological levels of 1,25(OH)2D3. The sterol and the Ca2+ channel agonist both increased 45Ca2+ transport 70% above control values within 2 min and 200% after 30 min of vascular perfusion. The effect of the Ca2+ channel agonist was dose dependent. Also, 1,25(OH)2D3-enhanced transcaltachia was abolished by the calcium channel blocker nifedipine. Collectively, these results suggest the involvement of 1,25(OH)2D3 in the activation of basal lateral membrane Ca2+ channels as an early effect in the transcaltachic response.