Two distinct membrane currents activated by cyclopiazonic acidinduced calcium store depletion in single smooth muscle cells of the mouse anococcygeus

摘要

1 By use of the whole-cell configuration of the patch-clamp technique, membrane currents induced by cyclopiazonic acid (CPA; an inhibitor of the sarcoplasmic reticulum (SR) calcium-ATPase) were investigated in single smooth muscle cells freshly dispersed from the mouse anococcygeus. Voltagedependent calcium currents were blocked with extracellular nifedipirie and caesium and tetraethylammonium chloride were used to block voltage-dependent potassium currents. 2 At a holding potential of -40 mV, CPA (10 μM) activated an inward current that consisted of two distinct components. The first was an initial transient current with an amplitude of 19.6 ± 1.9 pA while the second was sustained and had an amplitude of 3.5 ± 0.3 pA. 3 The current-voltage (Ⅰ-Ⅴ) relationship for the transient current showed marked outward rectification. The current had a reversal potential of 9.1 ± 1.1 mV which was shifted to 29.0 ± 4.2 mV when the extracellular chloride concentration was lowered from 148.4 to 58.4 mM. The sustained current had a near-linear Ⅰ-Ⅴ relationship and a reversal potential of 31.0 ± 2.7 mV. Removal of extracellular calcium had no effect on the transient current, but shifted the reversal potential of the sustained current to 18.2 ± 5.7 mV.