Polycystic kidney disease (PKD) is associated with alterations in developmental processes that severely affect kidney integrity, often leading to fatal consequences. It has been suggested that dysfunctional calcium (Ca2+) regulation associated with the PKD phenotype is consequent to mutations affecting the pkd1 gene. Previously, it has been observed that blocking calcium along with cAMP allowed tubular epithelial cells to enter the proliferative phase that culminated in a cyst-like phenotype. In this regard, mouse metanephroi, (embryonic day 13.5, E13.5) were used to study morphological and ultrastructural effects of calcium replenishment on 8-bromocyclic 3'5'cyclic adenosine monophosphate (8-Br-cAMP)-induced cyst-like tubular dilations. Phase contrast microscopy of 8-Br-cAMP-treated metanephroi exhibited numerous dilated tubules that continued to increase in size for 4 days in culture. The effects of 8-Br-cAMP on renal tubular epithelia were assessed by histopathological and electron microscopic analyses. Transmission electron microscopy revealed changes such as increased vacuolation, swollen mitochondria, chromatin condensation, and disrupted cell membrane in tubular epithelia of 8-Br-cAMP-treated metanephroi. Concurrent treatments with calcium-channel agonists (calcium ionophore A23187 and phorbol-12-myristate-13-acetate) and 8-Br-cAMP abolished cAMP-induced morphometric and ultrastructural alterations. Calcium replenishment rescued tubular epithelial cells from mitogenic effects of cAMP and restored normal morphology at cellular and sub-cellular levels as verified by histopathological and ultrastructural examinations.