5-Hydroxytryptamine-activated single-channel currents recorded from murine neuroblastoma cells

Differentiated murine neuroblastoma cells (NIE-115) have receptors for 5-hydroxytryptamine (5-HT), the activation of which either depolarizes or hyperpolarizes these cells with associated increases in input conductance. Ionophoresis of 5-HT on to NIE-115 cells elicits brief depolarization, but the 5-HT receptors rapidly desensitize during repeated application of 5-HT. The reversal potential of 5-HT-induced depolarization is ca. 0 mV. With the use of the improved patch clamp technique it is possible to record single ion channel currents activated by 5-HT from intact cells as well as isolated membrane patches. These currents are invariably inward at the resting potential (approximately 50 mV). The channel has a conductance of approximately 140 pS and reversal potential of approximately 0 mV in normal saline. The channels recorded from the intact cells reveal more than one kinetically distinguishable open and closed states. The kinetic properties of 5-HT channels recorded from excised patches of membrane (as outside-out) are different from those recorded from the intact cell. Possible explanations for such differences are presented.