State-dependent modification of ATP-sensitive K+ channels by phosphatidylinositol 4,5-bisphosphate.

With inside-out patch recordings in ventricular myocytes from the hearts of guinea pigs, we studied ATP-sensitive K+ (K(ATP)) channels activated by phosphatidylinositol 4,5-bisphosphate (PIP2) with respect to sensitivity to ATP when in either a rundown state (RS) or a non-rundown state (NRS). Rundown of K(ATP) channels was induced by exposure either to ATP-free solution or to ATP-free solution containing 19 microM Ca2+. Exposure of membrane patches to 10 microM PIP2 reactivated channels with both types of rundown. The reactivation by PIP2 did not require ATP in the bath. The IC50 of channels recovered from RS and before the rundown was 37.1 and 31.1 microM, respectively. PIP2 irreversibly increased the mean current when the channel was in the NRS. This was associated with a shift of IC50 to 250.6 microM after PIP2 exposure. PIP2 activates NRS K(ATP) channels by decreasing their sensitivity to ATP, whereas PIP2 reactivates RS-K(ATP) channels independently of ATP without changing ATP sensitivity.

On the mechanism of ADP-induced alteration of sulphonylurea sensitivity in cardiac ATP-sensitive K(+) channels.

1. To study the mechanism of regulation of sulphonylurea sensitivity in ATP-sensitive K(+) (K(ATP)) channels, we used the inside-out patch clamp technique in guinea-pig ventricular myocytes. 2. In the absence of nucleotides, the half maximal concentration of tolbutamide inhibition of K(ATP) channels (IC(50)) was 0.4 mM, and it decreased to 0.1 mM when 0.1 mM ATP was added. 3. Increasing the ADP concentration from 0 to 0.1 and 0.3 mM in the absence of ATP shifted the IC(50) from 0.4 to 5.3 and 11.4 mM, respectively. Increasing the ADP concentration further to 1 and 3 mM conversely reduced the IC(50) to 9.5 and 4.4 mM, respectively. 4. In the absence of Mg(2+) and ADP, the IC(50) was calculated to 16.6 mM which was found to be less, 12.3, 5.1 and 2.5 mM, respectively, when the ADP concentration was increased to 0.1, 0.3 and 1 mM. 5. The IC(50)s for tolbutamide obtained at various concentrations of ADP in the presence of Mg(2+) were best fitted by equations reflecting a model that assumed two binding sites for ADP; one is a high affinity site that reduces the sensitivity to the sulphonylurea, while the other is a low affinity site that increases such sensitivity. Dissociation constants calculated for ADP to sites 1 and 2 were 2.6 microM and 46.7 mM, respectively. In the absence of Mg(2+), data were fitted by equations corresponding to a single site model (site 2); the dissociation constant for ADP was 25.0 mM. 6. It is concluded that ADP modifies tolbutamide sensitivity by binding to two sites. The high affinity site is strongly Mg(2+)-dependent, whereas the low affinity site is Mg(2+)-independent.

Treatment of PCB-contaminated soil in a pilot-scale continuous decomposition system.

The BCDP (Base Catalyzed Decomposition Process) is a process by which difficult-to-decompose organic chlorine compounds, such as PCBs, are chemically decomposed and dechlorinated. Pilot-plant tests for PCB contaminated soil were carried out. PCB contaminated soil (32 mg/kg-530 mg/kg) was decontaminated to a level (0.038 mg/kg-4.8 mg/kg) which satisfied the corresponding Japanese environmental standard which stipulates, "there must be no discharge of PCB containing leachate".