Calcium-dependent chloride current in neurones of the rabbit pelvic parasympathetic ganglia

Abstract

1. Voltage-clamp recordings were made from neurones in rabbit vesical pelvic ganglia by using single microelectrodes filled with 2 M-caesium chloride. Neurones were superfused with Krebs solution containing 300 nM-tetrodotoxin and 50 mM-tetraethylammonium. 2. Depolarizing voltage jumps activated inward currents followed by slowly decaying inward tail currents at -30 to +30 mV, which were accompanied by a large increase in membrane conductance. Both the inward current and tail current were blocked by cobalt (2 mM) or in a Krebs solution containing zero calcium and 12 mM-magnesium. 3. Substitution of barium for calcium enhanced the inward current, while it strongly reduced the tail current. Strontium substitution still exhibited both the inward current and the tail current. 4. Lowering external chloride activity increased the tail current amplitudes without affecting an initial calcium current. The reversal potentials of the tail current, measured using a twin-pulse protocol, were -18 +/- 5 mV (mean +/- S.E.M., n = 8) and +5 +/- 3 mV (n = 5) in Krebs solution and low-chloride (62 mM) solution, respectively, suggesting a calcium-dependent chloride current. 5. Stilbene derivatives, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS, 0.01-1 mM) and 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS, 0.01-1 mM), reversibly and concentration dependently depressed the tail current without affecting the calcium current. 6. Transient (T) and sustained (N and L) types of calcium current were likely to co-exist in neurones of the rabbit pelvic ganglia. Calcium-dependent chloride current was activated by N- and L-type calcium currents but not by T-type current. 7. Activation of the tail current at 0 to +20 mV was described by a single-exponential function. The tail current decayed exponentially at a holding membrane potential of -70 mV. Tail decay time constants were dependent on voltage and duration of the step command. 8. Substantial activation of the calcium-dependent chloride conductance could occur during a post-tetanic after-potential when pelvic ganglia neurones fired action potentials repetitively.