Physiology Rapid diffusion of water across cell membranes depends on the presence of water channels, called aquaporins. Proximal convoluted tubule have: A Aquaporin 1 B Aquaporin 2 C Aquaporin 5 D Aquaporin 9 💡 Explanation Rapid diffusion of water across cell membranes depends on the presence of water channels, called aquaporins. Proximal convoluted tubule have: ✓ Correct Answer: A. Aquaporin 1