SPINAL SENSORY NEURONS EXPRESS MULTIPLE SODIUM-CHANNEL ALPHA-SUBUNIT MESSENGER-RNAS

The expression of sodium channel alpha-, beta 1- and beta 2-subunit mR NAs was examined in adult rat DRG neurons in dissociated culture at I day in vitro and within sections of intact ganglia by in situ hybridiz ation and reverse transcription polymerase chain reaction (RT-PCR). Th e results demonstrate that sodium channel alpha-subunit mRNAs are diff erentially expressed in small (<25 mu m diam.), medium (25-45 pm diam. ) and large (>45 mu m diam.) cultured DRG neurons at 1 day in vitro (d iv). Sodium channel mRNA I is expressed at higher levels in large neur ons than small DRG neurons, while sodium channel mRNA II is variably e xpressed, with most cells lacking or exhibiting low levels of detectab le signal of these mRNAs and limited numbers of neurons with moderate expression levels. DRG neurons generally exhibit negligible or low lev els of hybridization signal for sodium channel mRNA m. Sodium channel mRNAs Na6 and NaG show similar patterns of expression, with most large and many medium DRG neurons exhibiting high levels of expression. The mRNA for the rat cognate of human sodium channel hNE-Na is detected i n virtually every DRG neuron; most cells in all size classes exhibit m oderate or high levels of hNE-Na expression. Sodium channel SNS mRNA i s expressed in all size classes of DRG neurons, but shows greater expr ession in small and medium DRG neurons than in large neurons. The mRNA for the rat cognate of mouse sodium channel mNa,2.3 is not detected, or is detected at low levels, in most DRG neurons, regardless of size, although moderate expression is detected in some neurons. Sodium chan nel beta 1- and beta 2-subunit mRNAs exhibit similar expression patter ns; they are detected in most DRG neurons, although the level of expre ssion tends to be greater in large neurons than in small neurons. RT-P CR and in situ hybridization of intact adult DRG showed a similar patt ern of expression of sodium channel mRNAs to that observed in DRG neur ons in vitro. These results demonstrate that adult DRG neurons express multiple sodium channel mRNAs in vitro and in situ and suggest a mole cular basis for the biophysical heterogeneity of sodium currents obser ved in these cells.