Calcium‐activated chloride current in cultured sensory and parasympathetic quail neurones.

Abstract

SUMMARY1. Sensory (trigeminal and dorsal root) and autonomic (ciliary) ganglia from embryonic quail were dissociated and the neurones were grown in tissue culture.2. Intracellular recordings were made in voltage clamp using patch electrodes and the whole-cell recording technique. In order to investigate a calcium-activated chloride current, the sodium and potassium currents were blocked.3. Depolarizing voltage steps from a holding potential of -100 mV to a test potential of + 20 mV triggered an early inward and a delayed outward current. The latter persisted as a long-lasting inward tail current when the membrane was repolarized to -100 mV.4. These currents were all blocked by extracellular cobalt suggesting that they were calcium dependent. During a test depolarization to + 20 mV, in the presence of intracellular EGTA (20 mM), the inward current persisted but the outward current was suppressed. EGTA (20 mM) also suppressed the long-lasting inward tail current at -100 mV. This suggested the presence of a calcium-activated current.5. The reversal potential of the calcium-activated current was near the equilibrium potential for chloride ions and was shifted as predicted by the Nernst equation when the extracellular chloride concentration was changed.6. The calcium-activated current was partially blocked by adding 4-acetamido-4'-isothiocyanatostilbene-disulphonic acid (SITS) at a concentration of 1 mm to the external superfusion medium. This effect of a compound known to interfere with chloride channels together with the results of point (5) suggested the existence of a calcium-activated chloride current (ICi(ca)).7. ICca) could be activated by transient and sustained components of the calcium current present in the cultured neurones.8. ICi(ca) was present in 80 % of the sensory neurones but only in 10 % of the parasympathetic neurones.

Effects of metabolic blockers on Ca2+‐dependent currents in cultured sensory neurones from neonatal rats

“…The reduction of an adequate supply of ATP to neurones as occurs clinically in hypoxia, ischaemia or hypoglycaemia may precipitate the loss of intracellular Ca2" homeostasis and the subsequent triggering of a damaging cascade of Ca2+-dependent events leading ultimately to neuronal death (Siesj6, 1981 (Mayer, 1985;Bader et al, 1987;Akasu et at., 1990; but is also modulated by the efficiency with which Ca2" homeostatic mechanisms handle the intracellular Ca2" load Stapleton et al, 1992). Calcium-activated Cl-conductances can also be observed following very modest Ca2" entry during a single action potential recorded in the absence of K+ channel blockers (Mayer, 1985).…”

“…Measurements of both Ca2" induced inactivation of high voltage-activated Ca2" currents (Chad & Eckert, 1986) and Ca2"-activated Cltail currents (ICI(Ca)) (Owen et al, 1984;Mayer, 1985;Bader et al, 1987; act as physiological indices of [Ca2+], close to the cell plasma membrane. We have studied the effects of various metabolic insults on these currents used as indicators of the efficiency of neuronal Ca2+ homeostasis.…”

Calcium‐dependent chloride current induced by axotomy in rat sympathetic neurons.

“…In other neurons, inward calcium-dependent tail currents are carried by chloride ions (Mayer, 1985;Owen, Segal & Barker, 1986;Bader et al 1987;Akasu et al 1990). To test Pulse duration (ms) Figure 2.…”

“…In normal rat sympathetic ganglion cells, calcium entry during the action potential activates calcium-dependent potassium currents that produce the long AHP typical of these neurons (McAfee & Yarowsky, 1979;Belluzzi & Sacchi, 1990). On the other hand, Cl- (Owen, Segal & Barker, 1984;Mayer, 1985;Bader, Bertrand, & Schlichter, 1987;Akasu, Nishimura & Tokimasa, 1990; reviewed by Mayer, Owen & Barker, 1990) or cation currents (Partridge & Swandulla, 1988;Hasuo, Phelan, Twery & Gallagher, 1990) activated by calcium produce slow depolarizing after-potentials in several neuron types, but they have not been described in sympathetic ganglion cells. We have found that the ADP induced by axotomy is due to the activation of a Ca2+-dependent Cl-current. Part of this work has been presented in abstract form (Sanchez-Vives & Gallego, 1993 b).…”

Development of anomalous rectification (Ih) and of a tetrodotoxin‐resistant sodium current in embryonic quail neurones.

“…Embryos were decapitated at various ages and dorsal root ganglia (from the lumbo-sacral region), trigeminal ganglia and ciliary ganglia were dissected. The culture procedure were as previously described (Bader et al 1987) except that Minimum Essential Medium (MEM)-alpha (GIBCO) with 5% (v/v) heat-inactivated horse serum was used as a culture medium. After enzymatic and mechanical dissociation, the neurones were allowed to attach to the collagen-coated bottom of modified culture dishes (Bader et at.…”