Modulation of Ca2+-activated Cl- currents in rabbit portal vein smooth muscle by an inhibitor of mitochondrial Ca2+ uptake

1. The effects of carbonyl cyanide m-chlorophenyl hydrazone (CCCP), an inhibitor of mitochondrial Ca2+ uptake, was investigated on the properties of Ca2+-activated chloride currents (I-Cl(Ca)) in rabbit portal vein smooth muscle cells using the perforated patch whole cell voltage-clamp technique to ascertain whether this Ca2+ uptake process influences the time course of the subsarcolemmal Ca2+ signal that activates I-Cl(Ca). 2. In cells bathed in either physiological calcium (2 mM Ca-o(2+)) or high calcium (10 mM Ca-o(2+)) external solutions, application of CCCP (1-2 mu M) evoked an inward current and prolonged the exponential decay time constant (tau) of Ca2+-activated Cl- 'tail' currents (I-tail) evoked by Ca2+ influx through voltage-dependent calcium channels (VDCCs). The effect of CCCP on tau was greater in cells where the amplitude of I-tail was relatively large and, in different cells, the effect of CCCP on tau was positively correlated with the amplitude of I-tail. 3. CCCP abolished spontaneously occurring transient Ca2+-activated Cl- currents (STICs), but did not alter their time course before complete block. 4. Thapsigargin and cyclopiazonic acid (inhibitors of the sarcoplasmic Ca2+-ATPase) inhibited STICs, but did not affect the decay of I-tail or STICs. 5. In conclusion, when Ca2+ enters the cell through VDCCs, the time course of the consequent Ca2+ signal in the subsarcolemmal domain containing Ca2+-activated chloride channels appears to be regulated by Ca2+ uptake into mitochondria. In contrast, inhibition of Ca2+ uptake by the sarcoplasmic reticulum ATPase does not seem to influence the time course of I-Cl(Ca).