K+ homeostasis and central pattern generation in the metathoracic ganglion of the locust.
Stress-induced arrest of ventilatory motor pattern generation is tightly correlated with an abrupt increase in extracellular potassium concentration ([K+]o) within the metathoracic neuropil of the locust, Locusta migratoria. Na+/K+-ATPase inhibition with ouabain elicits repetitive surges of [K+]o that coincide with arrest and recovery of motor activity. Here we show that ouabain induces repetitive [K+]o events in a concentration-dependent manner. 10(-5)M, 10(-4)M, and 10(-3)M ouabain was bath-applied in semi-intact locust preparations. 10(-4)M and 10(-3)M ouabain reliably induced repetitive [K+]o events whereas 10(-5)M ouabain had no significant effect. In comparison to 10(-4)M ouabain, 10(-3)M ouabain increased the number and hastened the time to onset of repetitive [K+]o waves, prolonged [K+]o event duration, increased resting [K+]o, and diminished the absolute value of [K+]o waves. Recovery of motor patterning following [K+]o events was less likely in 10(-3)M ouabain. In addition, we show that K+ channel inhibition using TEA suppressed the onset and decreased the amplitude of ouabain-induced repetitive [K+]o waves. Our results demonstrate that ventilatory circuit function in the locust CNS is dependent on the balance between mechanisms of [K+] accumulation and [K+] clearance. We suggest that with an imbalance in favour of accumulation the system tends towards a bistable state with transitions mediated by positive feedback involving voltage-dependent K+ channels.
Rodgers
Corinne I
CI
Department of Biology, Queen's University, Biosciences Complex, Kingston, Ontario K7L 3N6, Canada. corinne.rodgers@queensu.ca
Labrie
John D
JD
Robertson
R Meldrum
RM
D000818:Animals; D017950:Ganglia, Sensory / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D019476:Insect Proteins / Q000378:metabolism; D048188:Locusta migratoria / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism*; D008297:Male; D019581:Neuropil / Q000187:drug effects / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D019476:Insect Proteins; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium