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With a breakdown of the vascular-CNS barrier, serum enters the nervous

With a breakdown of the vascular-CNS barrier, serum enters the nervous system. inhibited slightly. These changes in ion channel activity were associated with depolarization of the Mller cells. We hypothesized that activation of NSC channels would reduce the siphoning of K+ via the Mller cells. Consistent with this idea, ERGs from isolated retinas showed serum-induced reductions in the slow PIII component, which is generated by Mller cells responding to light-evoked changes in the extracellular K+ concentration. Lysophosphatidic acid (LPA), a component of serum, had effects on Mller cells that were qualitatively similar to those induced by serum. Our observations demonstrate that exposure to serum alters the activity of multiple types of ion channels in Mller glial cells of the mammalian retina. When there is a breakdown of the blood-retina barrier, LPA may be one of the serum-derived molecules which regulates the physiology of Mller cells. When there is a breakdown of the barrier between the circulatory and nervous systems, Rabbit Polyclonal to IKK-gamma the function of the CNS is compromised. Whilst gross tissue swelling and distortion due to an influx of Y-27632 2HCl distributor fluid from the vascular compartment can cause damage, knowledge of more subtle mechanisms by which a breakdown of this barrier alters function is limited. We hypothesize that serum-derived molecules enter the nervous system, induce receptor-mediated changes in cell function and thereby alter the activity of neural circuits. In this study, we examined the effect of serum on the activity of ion channels in glial cells. One reason the glia are of interest is that serum leaking from the vascular system Y-27632 2HCl distributor would almost certainly contact these cells, since they ensheath the blood vessels of the nervous system. We focused our study on the activity of ion channels, since they are involved in important glial functions such as the maintenance of K+ homeostasis (Newman & Reichenbach, 1996). Glial K+ channels are pathways for the redistribution of excess potassium. This redistribution via glial cells serves to limit wide swings in [K+]o which can alter neuronal excitability. To identify and characterize the effects of serum on glial channels, we chose to study Mller cells, the predominant glia of the retina. A reason for selecting these glial cells is that their role in K+ redistribution has been particularly well studied (Newman, 1995). By a specialized mechanism of K+ spatial buffering, termed K+ siphoning (Newman, Frambach & Odette, 1994), K+ enters a Mller cell where [K+]o is high and exits where [K+]o is lower. The extensive information concerning K+ siphoning via Mller cells facilitates attempts to relate changes in ion channel activity to the function of these cells in regulating [K+]o. Another motivation for studying retinal cells is that a breakdown of the blood-retinal barrier is a frequently occurring, sight-threatening pathophysiological process (Gass, 1997). Based on perforated-patch recordings from fresh bovine and human Mller cells, we now report that serum causes these glial cells to depolarize as a non-specific cation current and an outwardly rectifying K+ current are activated. In addition, the electroretinograms (ERGs) from isolated retinas exposed to serum showed changes consistent with the idea that the serum-induced changes in the activity of ion channels reduces the role of Mller cells in the redistribution of K+. We also found that lysophosphatidic acid (LPA), a component of serum, induces currents similar to those activated by whole serum. Thus, when there is a breakdown in the blood-retinal barrier, this glycerophospholipid may be one of the serum-derived molecules that regulates ion channel activity in Mller cells. METHODS Fresh Mller cells Freshly dissociated human and bovine Mller cells were prepared as detailed Y-27632 2HCl distributor previously (Kusaka, Dabin, Barnstable & Puro, 1996). In brief, approximately 0.5 cm 0.5 cm pieces of retina were incubated in Earle’s balanced salt solution supplemented with 0.5 mM EDTA, 1.5 mM CaCl2, 1 mM MgSO4, 20 mM glucose, 26 mM sodium bicarbonate, 15 u papain (Worthington Biochemicals Co.), 0.04% DNase, 2 mM cysteine and 12% chicken serum for 40 min at 30C, whilst 95% oxygen-5% CO2 was bubbled through to maintain pH and oxygenation. The piece of retina was then washed with the appropriate bathing solution, drawn up into a glass pipette and gently ejected back into a microcentrifuge tube..