Short Communication Patch-clamp Recording of Potassium Channels from Glial Cells in the Cockroach Central Nervous System

Glial cells in the insect nervous system are believed to play a role in regulating the extracellular potassium concentration, both during neuronal activity through spatial buffering (Gardner-Medwin, Coles & Tsacopoulos, 1981), and also by forming a blood-brain barrier (Schofield & Treherne, 1984). The membrane potential of glial cells has been thought to be exclusively dependent on potassium (Kettenmann, Sonnhof & Schachner, 1983), but recent studies on cultured glia have revealed conductance mechanisms for chloride (Coles & Orkand, 1984), sodium (Munson, Westermark & Glaser, 1979; Reiser, Loffler & Hamprecht, 1983) and calcium (MacVicar, 1984); and calcium and potassium channels have also been reported from in vivo retinal glial cells (Newman, 1985). This paper presents some patch-clamp recordings from in situ glial cells in the cockroach central nervous system. The ventral abdominal nerve cord from adult, male cockroaches (Periplaneta americana) was used throughout. The nerve cord was isolated and desheathed, using fine needles, between the 4th and 5th abdominal ganglia. This procedure removes the neural lamella and causes some damage to the underlying perineurial glial cells. However, all axons retain an intact layer of glial cells (C. A. Leech & L. S. Swales, unpublished observations). The nerve cord was then mounted in the experimental chamber and treated with a 1 % solution of collagenase (Sigma type 1-S, in cockroach saline) for 45min at room temperature. All experiments were performed at room temperature (20-23 °C). Normal cockroach saline contained (inmmolF): NaCl, 157; CaCl2, 2; MgCl2, 2; trehalose, 5; KOH, 3; Hepes, 10 (pH7-2). After enzyme treatment the cord was transferred to a '210K' saline: K2SO4, 105; Hepes, 10; trehalose, 5; MgSO4, 2; EGTA, 2; CaSO4, 1 (brought to pH7-2 with KOH giving a total [K] of about 220mmoll~, free [Ca] = 10~moll~). In some experiments, K2SO4 was partly replaced with Na2SO4. Patch pipettes were produced from borosilicate glass tube (Clark electromedical, GC120-15) and rilled with 210K saline containing 2 mmol I" CaSO4 (without EGTA). Currents were recorded using a Dagan 8900 amplifier with the output signal filtered at 1 kHz. Signals were recorded on tape (Racal Store 4) for