Transient changes in the size of the extracellular space in the sensorimotor cortex of cats in relation to stimulus-induced changes in potassium concentration.
The time course of local changes of the extracellular space (ES) was investigated by measuring concentration changes of repeatedly injected tetramethylammonium (TMA+) and choline (Ch+) ions for which cell membranes are largely impermeable. After stimulus-induced extracellular [K+] elevations the delta [TMA+] and delta [Ch+] signals recorded with nominally K+-selective liquid ion-exchanger microelectrodes increased by up to 100%, thus indicating a reduction of the ES down to one half of its initial size. The shrinkage was maximal at sites where the K+ release into the ES was also largest. At very superficial and deep layers, however, considerable increases in extracellular K+ concentration were not accompanied by significant reductions in the ES. These findings can be explained as a consequence of K+ movement through spatially extended cell structures. Calculations based on a model combining the spatial buffer mechanism of Kuffler and Nicholls (1966) to osmolarity changes caused by selective K+ transport through primarily K+ permeable membranes support this concept. Following stimulation additional iontophoretically induced [K+]0 rises were reduced in amplitude by up to 35%, even at sites where maximal decreases of the ES were observed. This emphasizes the importance of active uptake for K+ clearance out of the ES.
D000818:Animals; D002415:Cats; D002794:Choline / Q000378:metabolism; D004558:Electric Stimulation; D005110:Extracellular Space / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D011188:Potassium / Q000378:metabolism*; D012640:Seizures / Q000503:physiopathology; D013003:Somatosensory Cortex / Q000502:physiology*; D009435:Synaptic Transmission; D013787:Thalamic Nuclei / Q000502:physiology
D002794:Choline; D011188:Potassium