Fig. 2.

A: perfused SRGs. Glands were perfused with shark Ringer's solution for 30 min under basal conditions with measurements of chloride secretion every 10 min. At 30 min (arrow), 1-min readings were begun and glands were perfused with Ringer's solution containing either 8-bromo-cGMP (8 Br-cGMP; 100 μM; n = 4) or 8 Br-cGMP + PMA (100 μM; n = 3) or basal Ringer's only was continued as a control (n = 12). Whereas 8-Br-cGMP alone did not increase chloride secretion above basal levels, 8 Br-cGMP + PMA slightly increased chloride secretion from min 41–45 (P < 0.05) Values are mean chloride secretion (μeq·h⁻¹·g⁻¹) ± SE. B: representative I_sc experiment in primary culture monolayers of SRG tubular epithelial cells demonstrating a lack of response to 8 Br-cGMP and PMA, whereas CNP (0.05 μM) and 6 MB-cAMP markedly increased I_sc, which was inhibited to baseline by the addition of bumetanide (100 μM). The experiment is representative of 4 similar experiments.