Slow depolarizing potentials recorded from glial cells in the rat superficial dorsal horn.

Abstract

SUMMARY1. Intracellular potentials were recorded from inexcitable cells in the superficial dorsal horn of the rat lumbar spinal cord in vitro.2. These cells had a large resting membrane potential (up to -90 mV) but when depolarized were unable to produce action potentials. The resting potential was highly dependent upon extracellular K+ concentrations ([K+]0), with a slope of about 45 mV for a 10-fold change in [K+].3. Electrical stimulation of dorsal roots evoked a slow depolarizing potential lasting for many seconds in the inexcitable cells. The slow potentials were not accompanied by any appreciable change in input conductance, nor were their amplitudes dependent upon the membrane potential.4. The morphology of the inexcitable cells marked by intracellular injection of a fluorescent dye, Lucifer Yellow, was consistent with their being glial cells.5. [K+]. values were measured by K+-sensitive electrodes simultaneously with intracellular glial potentials. Changes in the K+-electrode potential occurred in parallel with slow depolarizing potentials following stimulation of dorsal roots. When the stimulus intensity was altered, changes in the magnitude of the K+-electrode response were correlated with those of the slow potentials.6. Replacement of extracellular Ca2+ by Mg2+ abolished both the slow potentials and K+-electrode responses evoked by afferent stimulation, suggesting that impulses in primary afferent fibres do not directly contribute to the glial slow potentials.7. It is concluded that the slow potentials in glial cells result from a transient increase in [K+]. at the superficial dorsal horn, which is induced by activation of neighbouring internuncial neurones.

Uneven distribution of excitatory amino acid receptors on ventral horn neurones of newborn rat spinal cord.

“…These cells, which had small cell bodies and many fine processes, did not generate an action potential. These cells were probably glial cells, as reported by Takahashi & Tsuruhara (1987).…”

Ionic and Volume Changes in the Microenvironment of Nerve and Receptor Cells

“…The notion that K+ released from activated primary afferent fibres depolarizes other primary afferents in the spinal cord was confirmed in experiments which demonstrated increased excitability of primary afferents (Fig. 1966) and mammalian (Takahashi and Tsuruhara 1987) glial cells. 31) during a Mg2+ or Mn2+ blockade of synaptic activity Sykova and Vyklicky 1977a;Nicoll 1979;Davidoff et al 1988).…”

Local Suppression of Epileptiform Activity by Electrical Stimulation in Rat Hippocampus In Vitro

“…Potassium‐selective microelectrodes measure an average potassium concentration at the interface of the bath and slice surface, and so underestimate the potassium concentration at the surface of the cells during endogenous potassium release. Current clamp (Takahashi & Tsuruhara, 1987; Traynelis & Dingledine, 1988) and voltage clamp (Chvatal et al 1999) recordings from glial cells, as well as modelling studies (Hounsgaard & Nicholson, 1983), approximate this underestimate at 25–75 %. Thus, in this study, the 2 m m increase measured by potassium‐selective electrodes during suprathreshold stimulation could reflect a ∼6 m m rise at the surface of cells which would result in depolarization block.…”