Calcium-activated chloride conductance in parasympathetic neurons of the rabbit urinary bladder

Intracellular recordings were made from vesical pelvic ganglion cells of the rabbit in a Krebs solution containing tetrodotoxin (1 microM). Experiments were carried out during complete suppression of the calcium-dependent potassium conductance by tetraethylammonium (greater than or equal to 20 mM) and/or intracellular injection of cesium ions. The action potential was followed by a depolarizing afterpotential which lasted for 0.3-10 s and had a peak amplitude of 5-20 mV at about -50 mV. The afterdepolarization (ADP) could not be observed when the preceding calcium-dependent action potential was blocked in a nominally calcium-free solution. Intracellular injection of ethyleneglycol-bis(beta-aminoethyl ether)N,N'-tetraacetic acid (EGTA) or total substitution of extracellular calcium ions with barium ions selectively blocked the ADP. The ADP, associated with an increased membrane conductance, reversed its polarity at -17 mV, when ganglion cells were impaled with microelectrodes filled with potassium chloride or cesium chloride. This reversal level was similar to that of the depolarization induced by gamma-aminobutyric acid. The reversal potential shifted to about -50 mV when acetate or sulphate were injected as counter anions. The peak amplitude and the total duration of the ADP was increased by substitution of external sodium chloride with sucrose or sodium isethionate. These results suggest that the ADP results from calcium entry during the spike and subsequent opening of chloride channels in parasympathetic neurons of the rabbit.