Functional involvement of sulphonylurea receptor (SUR) type 1 and 2B in the activity of pig urethral ATP-sensitive K+ channels

Abstract

1. We have investigated the possible roles of sulphonylurea receptor (SUR) type 1 and 2B in the activity of pig urethral ATP-sensitive K+ channels (KATP channels) by use of patch-clamp and reverse transcriptase - polymerase chain reaction (RT - PCR) techniques. 2. In voltage-clamp experiments, not only diazoxide, a SUR1 and weak SUR2B activator, but also pinacidil, a selective SUR2 activator, caused an inward current at a holding potential of -50 mV in symmetrical 140 mM K+ conditions. 3. Gliclazide (≤ 1 μM), a selective SUR1 blocker, inhibited the 10 μM pinacidil-induced currents (Ki = 177 μM) and the 500 μM diazoxide-induced currents (high-affinity site, Ki1 = 5 nM; low-affinity site, Ki2 = 108 μM) at -50 mV. 4. Application of tolbutamide (≤ 100 μM) reversibly caused an inhibition of the 500 μM diazoxide-induced current at -50 mV. 5. MCC-134, a SUR type-specific KATP channel regulator (1 - 100 μM), produced a concentration-dependent inward K+ current, which was suppressed by the application of glibenclamide at -50 mV. The amplitude of the MCC-134 (100 μM)-induced current was approximately 50% of that of the 100 μM pinacidil-induced currents. 6. Using cell-attached configuration, MCC-134 activated a glibenclamide-sensitive KATP channel which was also activated by pinacidil. 7. RT-PCR analysis demonstrated the presence of SUR1 and SUR2B transcripts in pig urethra. 8. These results indicate that both SUR1 and SUR2B subunits play a functional role in regulating the activity of pig urethral KATP channels and that SUR1 contributes less than 25% to total KATP currents.