Fig. 1.

Effects of forskolin and IBMX (F + I) on chloride secretion and AMPK activation in perfused shark rectal glands. All glands were perfused with elasmobranch Ringer’s bubbled with 99% O₂ and 1% CO_2. Baseline secretion levels were established for 30 min, before the addition of forskolin (1 µM) and IBMX (100 µM). Stimulation with F + I was carried out for 15 min. A: perfusion with F + I resulted in a rapid and sustained increase in chloride secretion (n = 5). Values are means ± SE; n = 5. P < 0.001 for all values from 30 to 45 min. B: glands were snap frozen in liquid N₂ and rectal gland homogenates were immunoblotted with specific antibodies against AMPKα (tAMPK), pThr¹⁷²AMPKα (pAMPK), and GAPDH. C: immunoblots were quantified with densitometry and pAMPK/tAMPK ratios were normalized to controls perfused with elasmobranch Ringer’s only (n = 5, ***P < 0.001, Student’s t-test).