作者:A. V. Zholos、C. J. Fenech、S. A. Prestwich、T. B. Bolton
DOI:10.1111/j.1469-7793.2000.00521.x
日期:2000.11
1. Using whole-cell patch-clamp recording techniques, we have examined voltage-gated ion currents in a cultured human intestinal smooth muscle cell line (HISM). Experiments were performed at room temperature on cells after passages 16 and 17.2. Two major components of the whole-cell current were a tetraethylammonium-sensitive (IC50 = 9 mM), iberiotoxin-resistant, delayed rectifier K+ current and a Na+ current inhibited by tetrodotoxin (IC50 approximate to 100 nM). No measurable inward current via voltage-gated Ca2+ channels could be detected in these cells even with 10 mM Ca2+ or Ba2+ in the external solution. No current attributable to calcium-activated K+ channels was found and no cationic current in response to muscarinic receptor activation was present.3. In divalent cation-free external solution two additional currents were activated: an inwardly rectifying hyperpolarization-activated current, I-HA, and a depolarization-activated current, I-DA.4. I-HA and I-DA could be carried by several monovalent cations; the sizes of currents in descending order were: K+ > Cs+ > Na+ for I-HA and Na+ > K+ much greater than Cs+ for I-DA. I-HA was activated and deactivated instantaneously and showed no inactivation whereas I-DA was activated, inactivated and deactivated within tens of milliseconds. These currents were inhibited by external calcium with an IC50 of 0.3 muM for I-DA and an IC50 of 20 muM for I-HA5. Cyclopiazonic acid (CPA) induced an outward, but not an inward current. SK&F 96365, a blocker of store-operated Ca2+ channels, suppressed I-DA With a. half-maximal inhibitory concentration of 9 muM but was ineffective in inhibiting I-HA at concentrations up to 100 muM. Gd3+ and La3+ strongly suppressed I-DA at 1 and 10 muM, respectively and were less effective in blocking I-HA (complete inhibition required a concentration of 100 muM for both). Carbachol at 10-100 muM evoked about a S-fold increase in I-HA amplitude and completely abolished I-DA.6. We conclude that I-HA and I-DA, are Ca2+-blockable cationic currents with different ion selectivity profiles that are carried by different channels. I-DA shows novel voltage-dependent properties for a cationic current.