Voltage-dependent sodium and potassium, but no calcium conductances in DDT1MF-2 smooth muscle cells
✍ Scribed by A. Molleman; A. Nelemans; J. Akker; M. Duin; A. Hertog
- Book ID
- 104745213
- Publisher
- Springer
- Year
- 1991
- Tongue
- English
- Weight
- 662 KB
- Volume
- 417
- Category
- Article
- ISSN
- 0031-6768
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✦ Synopsis
Voltage-dependent inward and outward membrane currents were investigated in the DDT1 MF-2 smooth muscle cell line using the whole-cell patch-clamp technique. Application of a pulse protocol with subsequent depolarizing voltage steps elicited an inactivating inward current and a non-inactivating outward current. The outward current was activated at membrane potentials more positive than -35 mY, with "Cac t = 30 -40 ms. The outward current was blocked by tetraethylammonium (NEt4C1) and 3,4-aminopyridine in a dose-dependent manner (ECs0 of 5 mM and 0.5 raM, respectively). The amplitude of the outward current was linked to the potassium equilibrium potential (Vek), and tail currents reversed near V~k. The outward current was completely abolished when intracellular potassium was substituted by 106 mM caesium and 20 mM NEt4C1. The inward current was activated at potentials more positive than -30 mV with tact of 1.6-2.5 ms, and with Z~nact of 1.7--3.0 ms. Steady-state inactivation was 50% at a holding potential of -40 inV. The inward current was blocked by tetrodotoxin (ECso of0.15 gM) and dependent on the reversal potential for sodium. Voltage-dependent calcium currents could not be detected. Further, the cytoplasmic free calcium concentration, as measured using Indo-1 fluorescence, was not changed during high-potassium(40 mM)-induced depolarization. In contrast, contraction of freshly obtained hamster vas deferens tissue elicited by high-potassium(40 mM)-induced depolarization was largely inhibited by diltiazem (20 IxM). These findings showed that voltage-dependent calcium channels are not functional in DDT~ MF-2 smooth muscle cells in contrast to freshly obtained Syrian hamster vas deferens smooth muscle. It is concluded that at least two populations of voltage-dependent channels are present in DDT1 MF-2 smooth muscle cells, conducting a slow outward rectifying current carried by potassium, and a fast, inactivating sodium current.