A GABA-activated chloride-conductance not blocked by picrotoxin on spiny lobster neuromuscular preparations.
Conductance increases to gamma-aminobutyric acid (GABA) were recorded in the gm6b and opener muscle of the spiny lobsters, Panulirus interruptus and P. argus. GABA-evoked responses were insensitive to picrotoxin at concentrations as high as 5 X 10(-5) M. Some blockade by picrotoxin was observed at higher concentrations. In normal physiological saline, the reversal potential of the Panulirus GABA-induced response was near the resting potential. The reversal potential was unaffected by reductions in sodium and calcium. Reduction of chloride by 50% resulted in a greater than 10 mV shift in the reversal potential of the GABA-induced response. Muscimol was able to mimic the action of GABA while baclofen was without effect. Bicuculline was a weak blocker. Avermectin B1a irreversibly increased the chloride permeability of the gm6b membrane. This conductance increase was blocked by picrotoxin over a range of concentrations similar to those required for blockade of the GABA-induced response. GABA-induced responses of the gm6b muscle of Homarus americanus were blocked almost completely by picrotoxin 10(-6) M. Sensitivity to picrotoxin is not invariably associated with GABA-activated chloride-mediated conductance increases. It is suggested that alteration in the binding-site for picrotoxin on the GABA-activated chloride-ion channel does not change other functional characteristics of the GABA-induced response.
Albert
J
J
Lingle
C J
CJ
Marder
E
E
O'Neil
M B
MB
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D004351:Drug Resistance; D066298:In Vitro Techniques; D007559:Ivermectin / Q000031:analogs & derivatives*; D007783:Lactones / Q000494:pharmacology; D009118:Muscimol / Q000494:pharmacology; D008121:Nephropidae; D009469:Neuromuscular Junction / Q000187:drug effects / Q000378:metabolism*; D010852:Picrotoxin / Q000494:pharmacology*; D013045:Species Specificity; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002712:Chlorides; D007559:Ivermectin; D007783:Lactones; D009118:Muscimol; D010852:Picrotoxin; D005680:gamma-Aminobutyric Acid; C022120:avermectin B(1)a