Astrocyte swelling underlying high extracellular K+ induced intrinsic optical signals

点击翻译按钮获取中文摘要

We investigated the cell types involved in generating intrinsic optical signals (IOS) and the roles for the Na K 2Cl cotransporter in activating cellular swelling in hippocampal slices. We monitored intrinsic optical signal (IOS) and astrocyte versus neuronal swelling in high external [K+] ([K+]ext). Increasing [K+]ext from 4.5 to 10 mM reversibly increased light transmittance through hippocampal slices even when spiking and excitatory synaptic transmission was blocked by TTX (12μM), AP-5 (100μM) and NBQX (20μM). Bumetanide (100μM), a selective Na-K-2Cl cotransporter antagonist, reversibly depressed the magnitude of the high [K+]ext-induced IOS to 50.2% of control. The monoclonal antibody, T4 which recognizes the NKCC1 isoform of the Na-K-2Cl cotransporter, detected a band of 〜180 kDa in western blots of hippocampal proteins. In the hippocampus robust immunostaining for NKCC1 was detected in both dendrites and somata of CA1 pyramidal neurons. Immunostaining of astrocytes was difficult to unequivocally ascertain in tissue sections. Therefore we examined acutely isolated astrocytes and found that GFAP +ve astrocytes were also immunoreactive for NKCC1. To determine whether astrocytes and/or neurons swelled in high [K+]ext we used two-photon laser scanning microscopy (TPLSM) to measure swelling in identified cells that were patched and filled with calcein. In high [K+]ext astrocyte processes increased their diameter to 126.5% whereas swelling was not observed in dendrites (98.0% of control). These results demonstrate that increased [K+]ext can induce glial swelling in the hippocampus principally by activation of the NKCC1 and that neurons defend their cell volume in high [K+]ext.