The influence of hypocarbia on the resolution of transient increases in brain extracellular potassium.
The effect of acute hypocarbia on baseline extracellular K+ concentration [( K+]e) and its effect on the ability of the cerebral microenvironment to recover from transient increases in [K+]e has been assessed in rats. Spreading depression of cortical activity was used to present a reproducible K+ load to the extracellular space. Baseline [K+]e and the half-time for resolution of the [K+]e changes seen with spreading depression waves were measured for the hypocarbic and normocarbic states by means of double-barrelled K+ microelectrodes placed approximately 400 micron below the cortical surface. Three spreading depression waves were initiated in each animal for the two CO2 states. In group 1 (n = 10), the rats were initially normocarbic (PaCO2 41.6 +/- 3.0 mmHg; mean +/- SD), then hypocarbic (PaCO2 19.0 +/- 2.5 mmHg) for the second series of measurements. The baseline [K+]e was significantly higher in the normocarbic state 3.4 +/- 0.4 versus 3.0 +/- 0.4 mM l-1, P less than 0.01 (paired t test). During normocarbia, the K+ load (delta[K+]e) presented to the extracellular space following spreading depression was 49.4 +/- 7.5 mM l-1, n = 10 (peak [K+]e - baseline [K+]e). The half-time for resolution of the presented [K+]e load was 24.3 +/- 6.1 s. Following hypocarbia of 1.4 +/- 0.6 h, there was no change in delta[K+]e (49.0 +/- 6.0 mM l-1) but resolution t1/2 had increased to 35.8 +/- 11.2 s, P less than 0.01 paired t test.(ABSTRACT TRUNCATED AT 250 WORDS)
D000768:Anesthesia, General; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002545:Brain Ischemia / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D013181:Cortical Spreading Depression; D005110:Extracellular Space / Q000378:metabolism; D008297:Male; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D013874:Thiopental
D002245:Carbon Dioxide; D013874:Thiopental; D011188:Potassium