Ca2+/calmodulin dependent protein kinase regulates GABA activated Cl- current in cockroach dorsal unpaired median neurons

We studied γ-aminobutyric acid (GABA)-mediated currents in short-term cultured dorsal unpaired median (DUM) neurons of cockroach Periplaneta americana using the whole cell patch-clamp technique in symmetrical chloride solutions. All DUM neurons voltage-clamped at −50 mV displayed inward currents (I GABA) when 10−4 M of GABA was applied by pneumatic pressure-ejection pulses. The semi-logarithmic curve ofI GABA amplitude versus the ejection time yielded a Hill coefficient of 4.0.I GABA was chloride (Cl−) because the reversal potential given by the current-voltage (I-V) curve varied according to the value predicted by the Nernst equation for Cl−dependence. In addition, I GABA was almost completely blocked by bath application of the chloride channel blockers picrotoxin (PTX) or 3,3-bis(trifluoromethyl)bicyclo-[2,2,1]heptane-2,2-diacarbonitrile (BIDN). The I-V curve forI GABA displayed a unexpected biphasic aspect and was best fitted by two linear regressions giving two slope conductances of 35.6 ± 2.1 and 80....