Figure 4. Alternative model for filling of the CVC.

Stimulation of an adenylyl cyclase results in a microtubule-dependent movement and fusion of acidocalcisomes with the CVC with transfer of membrane and matrix content. NH₃ enters the spongiome and combined with H⁺ pumped in by the V-H⁺-ATPase or the H⁺-PPase forms NH₄⁺ and increases the pH of the vacuole stimulating an exopolyphosphatase (PPX) to cleave polyP. Ammonium, Pi, and cations transferred by the different pumps and exchangers translocated from acidocalcisomes, are the osmolytes that attract water that enters through the aquaporin and swells the vacuole. When the vacuole enters in contact with the plasma membrane porosomes, Pi is transported back to the cytosol by the phosphate transporter (PHO1), while cations are also transported back to the cytosol by inversion of the exchangers. NH₄⁺ is transported to the cytosol through the ammonium transporter.