The Journal of Neurophysiology Vol. 77 No. 1 January 1997, pp. 236-246
Copyright ©1997 The American Physiological Society

TTX-Sensitive and -Resistant Na⁺ Currents, and mRNA for the TTX-Resistant rH1 Channel, Are Expressed in B104 Neuroblastoma Cells

Xiang Q. Gu, Sulayman Dib-Hajj, Marco A. Rizzo, and Stephen G. Waxman

Department of Neurology, Yale Medical School, New Haven, Connecticut 06510; and Neuroscience Research Center (127A), VA Medical Center, West Haven, Connecticut 06516

Gu, Xiang Q., Sulayman Dib-Hajj, Marco A. Rizzo, and Stephen G. Waxman. TTX-sensitive and -resistant Na⁺ currents, and mRNA for the TTX-resistant rH1 channel, are expressed in B104 neuroblastoma cells. J. Neurophysiol. 77: 236-246, 1997. To examine the molecular basis for membrane excitability in a neuroblastoma cell line, we used whole cell patch-clamp methods and reverse transcription-polymerase chain reaction (RT-PCR) to study Na⁺ currents and channels in B104 cells. We distinguished Tetrodotoxin (TTX)-sensitive and -resistant Na⁺ currents and detected the mRNA for the cardiac rH1 channel in B104 cells. Na⁺ currents could be recorded in 65% of cells. In the absence of TTX, mean peak Na⁺ current density was 126 ± 19 pA/pF, corresponding to a channel density of 2.7 ± 0.4/µ² (mean ± SE). Time-to-peak (t-peak), activation (_m), and inactivation time constants (_h) for Na⁺ currents in B104 cells were 1.0 ± 0.04, 0.4 ± 0.06, and0.9 ± 0.04 ms at 10 mV. The peak conductance-voltage relationship had a V_1/2 of 39.8 ± 1.5 mV. V_1/2 for steady-state inactivation was 81.6 ± 1.5 mV. TTX-sensitive and -resistant components of the Na current had half-maximal inhibitions (IC₅₀), respectively, of 1.2 nM and, minimally, 575.5 nM. The TTX-sensitive and-resistant Na⁺ currents were kinetically distinct; time-to-peak, _m, and _h for TTX-sensitive currents were shorter than for TTX-resistant currents. Steady-state voltage dependence of the two currents was indistinguishable. The presence of TTX-sensitive and-resistant Na⁺ currents, which are pharmacologically and kinetically distinct, led us to search for mRNAs known to be associated with TTX-resistant channels, in addition to the  subunit mRNAs, which have previously been shown to be expressed in these cells. Using RT-PCR and restriction enzyme mapping, we were unable to detect SNS, but detected mRNA for rH1, which is known to encode a TTX-resistant channel, in B104 cells. B104 neuroblastoma cells thus express TTX-sensitive and -resistant Na⁺ currents. These appear to be encoded by neuronal-type and cardiac Na⁺ channel mRNAs including the RH1 transcript. This cell line may be useful for studies on the rH1 channel, which is known to be mutated in the long-QT syndrome.

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