Limits...
Synaptically evoked glutamate transporter currents in Spinal Dorsal Horn Astrocytes.

Zhang H, Xin W, Dougherty PM - Mol Pain (2009)

Bottom Line: Pharmacological studies identified two subtypes of glutamate transporters in spinal astrocytes, GLAST and GLT-1.Glutamate transporter currents were graded with stimulus intensity, reaching peak responses at 4 to 5 times activation threshold, but were reduced following low-frequency (0.1 - 1 Hz) repetitive stimulation.These results suggest that glutamate transporters of spinal astrocytes could be activated by synaptic activation, and recording glutamate transporter currents may provide a means of examining the real time physiological responses of glial cells in spinal sensory processing, sensitization, hyperalgesia and chronic pain.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anesthesiology and Pain Medicine, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA. haijun.zhang@mdanderson.org

ABSTRACT

Background: Removing and sequestering synaptically released glutamate from the extracellular space is carried out by specific plasma membrane transporters that are primarily located in astrocytes. Glial glutamate transporter function can be monitored by recording the currents that are produced by co-transportation of Na+ ions with the uptake of glutamate. The goal of this study was to characterize glutamate transporter function in astrocytes of the spinal cord dorsal horn in real time by recording synaptically evoked glutamate transporter currents.

Results: Whole-cell patch clamp recordings were obtained from astrocytes in the spinal substantia gelatinosa (SG) area in spinal slices of young adult rats. Glutamate transporter currents were evoked in these cells by electrical stimulation at the spinal dorsal root entry zone in the presence of bicuculline, strychnine, DNQX and D-AP5. Transporter currents were abolished when synaptic transmission was blocked by TTX or Cd2+. Pharmacological studies identified two subtypes of glutamate transporters in spinal astrocytes, GLAST and GLT-1. Glutamate transporter currents were graded with stimulus intensity, reaching peak responses at 4 to 5 times activation threshold, but were reduced following low-frequency (0.1 - 1 Hz) repetitive stimulation.

Conclusion: These results suggest that glutamate transporters of spinal astrocytes could be activated by synaptic activation, and recording glutamate transporter currents may provide a means of examining the real time physiological responses of glial cells in spinal sensory processing, sensitization, hyperalgesia and chronic pain.

Show MeSH

Related in: MedlinePlus

Glutamate transporter currents recorded in spinal astrocytes reflect the intensity of synaptic activation. A-B, the amplitude of glutamate transporter currents recorded in a spinal astrocyte increases as the intensity of dorsal root entry zone stimulus increases (n = 14). The current reaches the maximal amplitude with 4 or 5 times threshold (T). C, normalization of responses in A to the same amplitude shows the same time course of each response.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2713213&req=5

Figure 3: Glutamate transporter currents recorded in spinal astrocytes reflect the intensity of synaptic activation. A-B, the amplitude of glutamate transporter currents recorded in a spinal astrocyte increases as the intensity of dorsal root entry zone stimulus increases (n = 14). The current reaches the maximal amplitude with 4 or 5 times threshold (T). C, normalization of responses in A to the same amplitude shows the same time course of each response.

Mentions: Single electrical stimuli delivered at the dorsal root entry zone evoked a large inward current in astrocytes held at a membrane potential of -80 mV (n = 15, Fig. 2). This inward current decayed slowly, often lasting over 10 seconds. In the presence of Ba2+, the slowly decaying inward current was blocked and a fast inward current unmasked (n = 15, Fig. 2). The fast inward currents were characterized by rapid onset with a rising τ of 3.3 ± 0.3 ms, relatively slow decay τ of 11.3 ± 0.6 ms and half decay time of 13.9 ± 0.3 ms when evoked by maximal (5 × threshold) stimuli (n = 15, Fig. 3A). Stimulus evoked inward currents in astrocytes were strongly, but reversibly, inhibited by addition of cadmium (CdCl2, 40 μM, n = 3) or tetrodotoxin (TTX, 1 μM, n = 4) to the bath to block presynaptic calcium channels and voltage-sensitive sodium channels, respectively (Fig. 4). Thus, glutamate transporter currents elicited in response to dorsal root entry zone stimulation is dependent on the synaptic release of glutamate. The minimal intensity threshold stimulus to evoke glutamate transporter currents ranged between 0.5 and 1.0 mA. The mean amplitude of transporter currents at threshold stimulation was 18.4 ± 1.7 pA (n = 14). Increases in stimulus intensity resulted in an increase in evoked glutamate transporter current amplitude to a maximal mean response of 77.7 ± 7.4 pA (n = 14) evoked at 4 to 5 times threshold strength (Fig. 3A, B). The time course of glutamate transporter currents evoked by varying stimulus strength was assessed by scaling each of the responses to the amplitude of the maximal response. The overlay of these scaled currents shown in Fig. 3C indicates that the stronger stimuli did not change the time course of evoked glutamate transporter currents.


Synaptically evoked glutamate transporter currents in Spinal Dorsal Horn Astrocytes.

Zhang H, Xin W, Dougherty PM - Mol Pain (2009)

Glutamate transporter currents recorded in spinal astrocytes reflect the intensity of synaptic activation. A-B, the amplitude of glutamate transporter currents recorded in a spinal astrocyte increases as the intensity of dorsal root entry zone stimulus increases (n = 14). The current reaches the maximal amplitude with 4 or 5 times threshold (T). C, normalization of responses in A to the same amplitude shows the same time course of each response.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2713213&req=5

Figure 3: Glutamate transporter currents recorded in spinal astrocytes reflect the intensity of synaptic activation. A-B, the amplitude of glutamate transporter currents recorded in a spinal astrocyte increases as the intensity of dorsal root entry zone stimulus increases (n = 14). The current reaches the maximal amplitude with 4 or 5 times threshold (T). C, normalization of responses in A to the same amplitude shows the same time course of each response.
Mentions: Single electrical stimuli delivered at the dorsal root entry zone evoked a large inward current in astrocytes held at a membrane potential of -80 mV (n = 15, Fig. 2). This inward current decayed slowly, often lasting over 10 seconds. In the presence of Ba2+, the slowly decaying inward current was blocked and a fast inward current unmasked (n = 15, Fig. 2). The fast inward currents were characterized by rapid onset with a rising τ of 3.3 ± 0.3 ms, relatively slow decay τ of 11.3 ± 0.6 ms and half decay time of 13.9 ± 0.3 ms when evoked by maximal (5 × threshold) stimuli (n = 15, Fig. 3A). Stimulus evoked inward currents in astrocytes were strongly, but reversibly, inhibited by addition of cadmium (CdCl2, 40 μM, n = 3) or tetrodotoxin (TTX, 1 μM, n = 4) to the bath to block presynaptic calcium channels and voltage-sensitive sodium channels, respectively (Fig. 4). Thus, glutamate transporter currents elicited in response to dorsal root entry zone stimulation is dependent on the synaptic release of glutamate. The minimal intensity threshold stimulus to evoke glutamate transporter currents ranged between 0.5 and 1.0 mA. The mean amplitude of transporter currents at threshold stimulation was 18.4 ± 1.7 pA (n = 14). Increases in stimulus intensity resulted in an increase in evoked glutamate transporter current amplitude to a maximal mean response of 77.7 ± 7.4 pA (n = 14) evoked at 4 to 5 times threshold strength (Fig. 3A, B). The time course of glutamate transporter currents evoked by varying stimulus strength was assessed by scaling each of the responses to the amplitude of the maximal response. The overlay of these scaled currents shown in Fig. 3C indicates that the stronger stimuli did not change the time course of evoked glutamate transporter currents.

Bottom Line: Pharmacological studies identified two subtypes of glutamate transporters in spinal astrocytes, GLAST and GLT-1.Glutamate transporter currents were graded with stimulus intensity, reaching peak responses at 4 to 5 times activation threshold, but were reduced following low-frequency (0.1 - 1 Hz) repetitive stimulation.These results suggest that glutamate transporters of spinal astrocytes could be activated by synaptic activation, and recording glutamate transporter currents may provide a means of examining the real time physiological responses of glial cells in spinal sensory processing, sensitization, hyperalgesia and chronic pain.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anesthesiology and Pain Medicine, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA. haijun.zhang@mdanderson.org

ABSTRACT

Background: Removing and sequestering synaptically released glutamate from the extracellular space is carried out by specific plasma membrane transporters that are primarily located in astrocytes. Glial glutamate transporter function can be monitored by recording the currents that are produced by co-transportation of Na+ ions with the uptake of glutamate. The goal of this study was to characterize glutamate transporter function in astrocytes of the spinal cord dorsal horn in real time by recording synaptically evoked glutamate transporter currents.

Results: Whole-cell patch clamp recordings were obtained from astrocytes in the spinal substantia gelatinosa (SG) area in spinal slices of young adult rats. Glutamate transporter currents were evoked in these cells by electrical stimulation at the spinal dorsal root entry zone in the presence of bicuculline, strychnine, DNQX and D-AP5. Transporter currents were abolished when synaptic transmission was blocked by TTX or Cd2+. Pharmacological studies identified two subtypes of glutamate transporters in spinal astrocytes, GLAST and GLT-1. Glutamate transporter currents were graded with stimulus intensity, reaching peak responses at 4 to 5 times activation threshold, but were reduced following low-frequency (0.1 - 1 Hz) repetitive stimulation.

Conclusion: These results suggest that glutamate transporters of spinal astrocytes could be activated by synaptic activation, and recording glutamate transporter currents may provide a means of examining the real time physiological responses of glial cells in spinal sensory processing, sensitization, hyperalgesia and chronic pain.

Show MeSH
Related in: MedlinePlus