Heterogeneous response of cytoplasmic free Ca2+ in proximal convoluted and straight tubule cells in primary culture.

Cytoplasmic free calcium [( Ca2+]c) plays an important role in cellular signal transduction in response to hormones. The development of microfluorometric digital image analysis makes it possible to obtain an image of a calcium-indicator dye, fura-2, in a single living cell. Subconfluent primary cultured cells from isolated proximal convoluted and straight tubules were analyzed for [Ca2+]c. The basal level of [Ca2+]c was 92.0 +/- 0.82 nM in convoluted and 75.0 +/- 4.7 nM in straight tubule cells. Exposure of convoluted tubule cells to parathyroid hormone (10(-7) M) elicited a 1.4-fold transient rise in [Ca2+]c. Treatment of straight tubule cells with calcitonin (0.1 U/ml), on the other hand, evoked a 1.6-fold transient increase in [Ca2+]c. [Ca2+]c in proximal straight tubule cells did not respond to parathyroid hormone, nor did that in convoluted tubule cells to calcitonin. [Ca2+]c peaks were diminished in straight tubule cells by repeated additions of calcitonin at 5-min intervals. These hormonal responses were abolished by perfusing the cells with calcium-free solution and were not mimicked by perfusion with adenosine 3',5'-cyclic monophosphate (10(-4) M) or with forskolin (5 X 10(-5) M). The results suggest that the [Ca2+]c response to the selected peptide hormones is different in proximal convoluted and straight tubule cells in primary culture.