Figure 6.

Hydrolysis of GTP is required for normal exocytosis and endocytosis in IHCs. IHCs in acute explants of P14–P17 organs of Corti were patch clamped in ruptured patch configuration, with either 0.3 mm GTP (black), 0 mm GTP (dark gray), or 0.3 mm GTPγS (light gray) in the patch pipette. A, GTPγS-infused cells exhibit rapid increases in C_m, as opposed to the decrease found in GTP-infused cells. Bold lines represent the grand average, with the numbers at each point indicating the number of cells used in the average. C_m was monitored by repetitive 2-s-long recordings, of which the average is displayed. Most (9 of 13) cells treated with GTPγS showed a continuous C_m increase in membrane surface, whereas two showed a rapid C_m increase, followed by a C_m decline and another two showed a continuous C_m decline over the entire experiment. All control cells showed a continuous decline over the entire experiment. Some (3 of 10) cells infused with a GTP-free intracellular solution showed a slight increase of C_m, one showed constant C_m, and the rest showed a continuous decline over the entire experiment. B, Average ΔC_m responses of the IHCs to 200 ms depolarizations to −14 mV in the presence of 0.3 mm GTPγS (light gray), 0 mm GTP (dark gray), or 0.3 mm GTP (black). Infusion of GTPγS blocks endocytosis and also reduces the amount of exocytosis, whereas lack of GTP leads to reduced exocytosis and a trend toward slower endocytosis (time constant of 8.3 ± 2.2 s without GTP vs 4.6 ± 1.1 with GTP, p = 0.16, one GTP-free recording did not show an exponential component of retrieval).