Properties of the transient K+ current in acutely isolated supraoptic neurons from adult rat

Abstract

The transient outward current (I(TO)) in magnocellular neurosecretory cells was studied using whole cell patch clamp recordings made from supraoptic neurons acutely isolated from the adult rat. In the presence of tetrodotoxin, depolarizing steps applied from a negative holding potential evoked a rapidly activating and inactivating outward current followed by a slowly activating and sustained outward current. The I(TO) was unaffected by tetraethylammonium (TEA), but was blocked by 4-aminopyridine. The I(TO) evoked by depolarization from negative potentials in the presence of 40 mM TEA was not different from that revealed by digital subtraction of current traces recorded with and without a negative conditioning prepulse in control solutions. Tail current analysis during perfusion of media containing different external [K+] indicated that I(TO) is selective for K+ ions. Exposure to Ca2+-free solutions containing divalent inorganic cations such as Cd2+ and Ni2+ could cause shifts in voltage-dependency and, thereby, reduce the amplitude of I(TO) recorded at fixed submaximal potentials. The maximal I(TO) achievable under these conditions, however, was reduced compared to control. Moreover, the I(TO) was also reduced by application of organic Ca2+ channel antagonists such as nifedipine and ω-conotoxin GVIA, indicating that a component of the I(TO) is somehow dependent on Ca2+ influx.