Subclassified acutely dissociated cells of rat DRG: histochemistry and patterns of capsaicin-, proton-, and ATP-activated currents.
We used a "current signature" method to subclassify acutely dissociated dorsal root ganglion (DRG) cells into nine subgroups. Cells subclassified by current signature had uniform properties. The type 1 cell had moderate capsaicin sensitivity (25.9 pA/pF), powerful, slowly desensitizing (tau = 2,300 ms), ATP-activated current (13.3 pA/pF), and small nondesensitizing responses to acidic solutions (5.6 pA/pF). Type 1 cells expressed calcitonin gene-related peptide immunoreactivity (CGRP-IR), manifested a wide action potential (7.3 ms), long duration afterhyperpolarization (57.0 ms), and were IB4 positive. The type 2 cell exhibited large capsaicin activated currents (134.9 pA/pF) but weak nondesensitizing responses to protons (15.3 pA/pF). Currents activated by ATP and alphabeta-m-ATP (51.7 and 44.6 pA/pF, respectively) had fast desensitization kinetics (tau = 214 ms) that were distinct from all other cell types. Type 2 cells were IB4 positive but did not contain either substance P (SP) or CGRP-IR. Similar to capsaicin-sensitive nociceptors in vivo, the afterhyperpolarization of the type 2 cell was prolonged (54.7 ms). The type 3 cell expressed, amiloride-sensitive, rapidly desensitizing (tau = 683 ms) proton-activated currents (127.0 pA/pF), and was insensitive to ATP or capsaicin. The type 3 cell was IB4 negative and contained neither CGRP nor SP-IR. The afterhyperpolarization (17.5 ms) suggested nonnociceptive function. The type 4 cell had powerful ATP-activated currents (17.4 pA/pF) with slow desensitization kinetics (tau = 2, 813 ms). The afterhyperpolarization was prolonged (46.5 ms), suggesting that this cell type might belong to a capsaicin-insensitive nociceptor population. The type 4 cell did not contain peptides. The type 7 cell manifested amiloride-sensitive, proton-activated currents (45.8 pA/pF) with very fast desensitization kinetics (tau = 255 ms) and was further distinct from the type 3 cell by virtue of a nondesensitizing amiloride-insensitive component (6.0 pA/pF). Capsaicin and ATP sensitivity were relatively weak (4.3 and 2.9 pA/pF, respectively). Type 7 cells were IB4 positive and contained both SP and CGRP-IR. They exhibited an exceptionally long afterhyperpolarization (110 ms) that was suggestive of a silent (mechanically insensitive) nociceptor. We concluded that presorting of DRG cells by current signatures separated them into internally homogenous subpopulations that were distinct from other subclassified cell types.
Petruska
J C
JC
Department of Neuroscience, McKnight Brain Institute, University of Florida College of Medicine, Gainesville, Florida 32610, USA.
Napaporn
J
J
Johnson
R D
RD
Gu
J G
JG
Cooper
B Y
BY
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis; D002211:Capsaicin / Q000494:pharmacology*; D016000:Cluster Analysis; D005727:Ganglia, Spinal / Q000737:chemistry / Q000166:cytology*; D037102:Lectins / Q000494:pharmacology; D008297:Male; D009475:Neurons, Afferent / Q000737:chemistry / Q000145:classification* / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology; D010146:Pain / Q000503:physiopathology; D018408:Patch-Clamp Techniques; D011522:Protons; D051381:Rats; D017207:Rats, Sprague-Dawley; D013373:Substance P / Q000032:analysis
D037102:Lectins; D011522:Protons; D013373:Substance P; D000255:Adenosine Triphosphate; D015740:Calcitonin Gene-Related Peptide; D002211:Capsaicin