Potassium channels of myenteric neurons in guinea-pig small intestine

Patch-clamp recording was used to study rectifying K+ currents in myenteric neurons in short-term culture. In conditions that suppressed Ca2+-activate d K+ current, three kinds of voltage activated K+ currents were identified by their voltage range of activation, inactivation, kinetics and pharmacolo gy. These were A-type current, delayed outwardly rectifying current (I-K,I- dr) and inwardly rectifying current (I-K,I-ir). I-K,I-ir consisted of an in stantaneous component followed by a time-dependent current that rapidly inc reased at potentials negative to -80 mV. Time-constant of activation was vo ltage-dependent with an e-fold decrease for a 31-mV hyperpolarization amoun ting to a decrease from 800 to 145 ms between -80 and -100 mV. I-K,I-ir did not inactivate. I-K,I-ir was abolished in K+-free solution. Increases in e xternal K+ increased I-K,I-ir conductance in direct relation to the square root of external K+ concentration. Activation kinetics were accelerated and the activation range shifted to more positive K+ equilibrium potentials. I -K,I-ir was suppressed by external Cs+ and Ba2+ in a concentration-dependen t manner. Ca2+ and Mg2+ were less effective than Ba2+. I-K,I-ir was unaffec ted by tetraethylammonium ions. I-K,I-dr was activated at membrane potentia ls positive to -30 mV with an e-fold decrease in time-constant of activatio n from 145 to 16 ms between - 20 and 30 mV. It was half-activated at 5 mV a nd fully activated at 50 mV. Inactivation was indiscernible during 2.5 s te st pulses. I-K,I-dr was suppressed in a concentration-, but not voltage-dep endent manner by either tetraethylammonium or 4-aminopyridine and was insen sitive to Cs+. The results suggest that I-K,I-ir may be important in maintaining the high resting membrane potentials found in afterhyperpolarization-type enteric ne urons. They also suggest importance of I-K,I-ir channels in augmentation of the large hyperpolarizing after-potentials in afterhyperpolarization-type neurons and the hyperpolarization associated with inhibitory postsynaptic p otentials. I-K,I-dr in afterhyperpolarization-type enteric neurons has over all kinetics and voltage behaviour like delayed rectifier currents in other excitable cells where the currents can also be distinguished from A-type a nd Ca2+-activated K+ current. (C) 1998 IBRO. Published by Elsevier Science Ltd.