PHYSIOLOGICAL AND MOLECULAR CHARACTERIZATION OF AN IRK-TYPE INWARD RECTIFIER K-CELL LINE( CHANNEL IN A TUMOR MAST)

The basophilic leucaemia cell line RBL-2H3 exhibits a robust inwardly rectifying potassium current, I-KIR, which is likely to be modulated b y G proteins. We examined the physiological and molecular properties o f this K-IR conductance to define the nature of the underlying channel species. The macroscopic conductance revealed characteristics typical of classical Kf inward rectifiers of the IRK type. Channel gating was rapid, first order (tau approximate to 1 ms at -100 mV) and steeply v oltage dependent. Both activation potential and slope conductance were dependent on extracellular K+ concentration ([K+](o)) and inward rect ification persisted in the absence of internal Mg2+. The current was s usceptible to a concentration- and voltage-dependent block by extracel lular Na+, Cs+ and Ba2+. Initial I-KIR whole-cell amplitudes as well a s current rundown were dependent on the presence of 1 mM internal ATP. Perfusion of intracellular guanosine 5'-Q-(3-thiotriphosphate) (GTP[g amma S]) suppressed I-KIR with an average half-time of decline of appr oximately 400 s. It was demonstrated that the dominant IRK-type 25 pS conductance channel was indeed suppressed by 100 mu M preloaded GTP[ga mma S]. Reverse transcriptase-polymerase chain reactions (RT-PCR) with RBL cell poly(A)(+) RNA identified a full length K+ inward rectifier with 94% base pair homology to the recently cloned mouse IRK1 channel. It is concluded that RBL cells express a classical voltage-dependent IRK-type K+ inward rectifier RBL-IRK1 which is negatively controlled b y G proteins.