VOLTAGE-GATED SODIUM-CHANNELS IN HUMAN AORTIC SMOOTH-MUSCLE CELLS

Whole-cell, voltage clamp methods were used to study inward currents i n human aortic smooth muscle cells in culture. Cells were plated on gl ass coverslips, cultured in supplemented M-199 media with 5% serum and studied as primary cells and at passages 2-5. Inward currents were me asured with a pipette solution containing Cs+ and TEA(+) to block K+ c urrents and with 2.5 mM [Ca2+](0) in the perfusate. Inward currents ac tivated at about -50 mV, peaked at about -15 mV and reversed at about +30 mV. Values of peak inward current averaged 14.7 +/- 3.3 pA/pF and cell capacitance averaged 124 +/- 10 pF (n = 35), These currents activ ated rapidly with a time-to-peak current of 2.4 +/- 0.3 ms at a test p otential of -10 mV from a holding potential of -80 mV, The current als o inactivated rapidly with a time course that could be described by tw o components with time constants of 1.8 +/- 0.2 and 17.8 +/- 3.5 ms at -10 mV, The currents decreased when extracellular Na+ was reduced and were completely inhibited by 50 nM tetrodotoxin (TTX), suggesting tha t they represented voltage-gated Na+ currents (I-Na). Activation curve s were characterized with a V-0.5 = -16.6 +/- 2.4 mV and a slope facto r k = -5.2 +/- 0.2 mV while inactivation curves were characterized wit h a V-0.5 = -60.9 +/- 1.7 mV and a slope factor k = 8.8 +/- 0.4 mV. Lo wering external [Ca2+] to zero increased the maximum I-Na, Shifted its voltage dependence in the hyperpolarizing direction and increased the rate of I-Na inactivation. Increasing external [Ca2+] or [Mg2+]decrea sed I-Na and slowed its rate of inactivation. These studies demonstrat e the presence of voltage-gated Na+ channels with high TTX sensitivity that are modulated by extracellular divalent cations in human aortic smooth muscle cells maintained in cell culture. Window currents were f ound in the voltage range of -50 to -20 mV, suggesting that these chan nels could contribute to the resting membrane potential.