Fig. 1.

A: perfused shark rectal glands (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 forskolin (1 μM + IBMX 100 μM; n = 13) or C-type natriuretic peptide (CNP; 10 nM; n = 10) or basal Ringer's only was continued as a control (n = 10). Values are mean chloride secretion (μeq·h⁻¹·g⁻¹) ± SE. B: representative short circuit current (I_sc) experiment in primary culture monolayers of SRG tubular epithelial cells demonstrating the response to CNP (0.05 μM), followed by forskolin (10 μM). I_sc was then inhibited by the addition of bumetanide (100 μM) and BaCl₂ (10 mM). This experiment is representative of 4 similar experiments.