CATION CURRENT ACTIVATED BY HYPERPOLARIZATION (IH) IN GUINEA-PIG ENTERIC NEURONS

Intracellular microelectrode and whole cell patch-clamp recordings were made from guinea pig enteric neurons in vitro. In most myenteric AH neurons (but not S neurons), step hyperpolarizations from the resting potential evoked an inward current (I(H)). I(H) peaked in approximately 400 ms (at 36-degrees-C), was fully activated at -100 mV, and did not inactivate during 10 s. I(H) was associated with a conductance increase and reversed polarity at about -40 mV (by extrapolation). I(H) was reduced in low-sodium concentrations and increased when the concentration of extracellular potassium ions was increased. Cesium (2 mM) blocked I(H) in a voltage-dependent manner; this led to an increase in the amplitude of the spike after-hyperpolarization. Cobalt (2-4 mM) or barium (0.01-1 mM) did not alter I(H). Only 12% of submucous plexus neurons showed I(H) and this subgroup included both S and AH neurons. In myenteric AH neurons, I(H) would act in opposition to the persistent calcium-activated potassium current and thus stabilize the resting potential.