Forskolin Stimulation of Water and Cation Permeability in Aquaporin1 Water Channels

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Abstract
Aquaporin1, a six-transmembrane domain protein, is a water channel present in many fluid-secreting and -absorbing cells. In Xenopus oocytes injected with aquaporin1 complementary RNA, the application of forskolin or cyclic 8-bromo- adenosine 3′,5′-monophosphate increased membrane permeability to water and triggered a cationic conductance. The cationic conductance was also induced by direct injection of protein kinase A (PKA) catalytic subunit, reduced by the kinase inhibitor H7, and blocked by HgCl2, an inhibitor of aquaporin1. The cationic permeability of the aquaporin1 channel is activated by a cyclic adenosine monophosphate-dependent mechanism that may involve direct or indirect phosphorylation by PKA.