Voltage-gated calcium currents in axotomized adult rat cutaneous afferent neurons.
The effect of sciatic nerve injury on the somatic expression of voltage-gated calcium currents in adult rat cutaneous afferent dorsal root ganglion (DRG) neurons identified via retrograde Fluoro-gold labeling was studied using whole cell patch-clamp techniques. Two weeks after a unilateral ligation and transection of the sciatic nerve, the L(4)-L(5) DRG were dissociated and barium currents were recorded from cells 3-10 h later. Cutaneous afferents (35-50 microm diam) were classified as type 1 (possessing only high-voltage-activated currents; HVA) or type 2 (having both high- and low-voltage-activated currents). Axotomy did not change the percentage of neurons exhibiting a type 2 phenotype or the properties of low-threshold T-type current found in type 2 neurons. However, in type 1 neurons the peak density of HVA current available at a holding potential of -60 mV was reduced in axotomized neurons (83.9 +/- 5.6 pA/pF, n = 53) as compared with control cells (108.7 +/- 6.9 pA/pF, n = 58, P < 0.01, unpaired t-test). A similar reduction was observed at more negative holding potentials, suggesting differences in steady-state inactivation are not responsible for the effect. Separation of the type 1 cells into different size classes indicates that the reduction in voltage-gated barium current occurs selectively in the larger (capacitance >80 pF) cutaneous afferents (control: 112.4 +/- 10.6 pA/pF, n = 30; ligated: 72.6 +/- 5.0 pA/pF, n = 36; P < 0.001); no change was observed in cells with capacitances of 45-80 pF. Isolation of the N- and P¿Q-type components of the HVA current in the large neurons using omega-conotoxin GVIA and omega-agatoxin TK suggests a selective reduction in N-type barium current after nerve injury, as the density of omega-CgTx GVIA-sensitive current decreased from 56.9 +/- 6.6 pA/pF in control cells (n = 13) to 31.3 +/- 4.6 pA/pF in the ligated group (n = 12; P < 0.005). The HVA barium current of large cutaneous afferents also demonstrates a depolarizing shift in the voltage dependence of inactivation after axotomy. Injured type 1 cells exhibited faster inactivation kinetics than control neurons, although the rate of recovery from inactivation was similar in the two groups. The present results indicate that nerve injury leads to a reorganization of the HVA calcium current properties in a subset of cutaneous afferent neurons.
Baccei
M L
ML
Department of Neurology, Yale University School of Medicine, New Haven 06510, USA.
Kocsis
J D
JD
D000818:Animals; D019771:Axotomy; D001464:Barium / Q000493:pharmacokinetics; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000502:physiology*; D020747:Calcium Channels, T-Type / Q000502:physiology; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology; D015640:Ion Channel Gating / Q000502:physiology*; D009475:Neurons, Afferent / Q000737:chemistry* / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D012867:Skin / Q000294:innervation*; D013569:Synapses / Q000737:chemistry / Q000502:physiology; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D001464:Barium; D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D020747:Calcium Channels, T-Type; D020866:omega-Conotoxin GVIA