Effect of histamine on the membrane potential of cultured human nonpigmented ciliary epithelial cells.

The effect of histamine on the membrane potential of cultured human nonpigmented ciliary epithelial cells was examined using intracellular microelectrodes. The resting voltage was Vm = 42 +/- 0.7 mV (n = 41). Histamine (10(-6) mol/l) induced transient hyperpolarization (V = 19.4 +/- 1.2 mV, n = 35) and subsequent depolarization when applied for more than 1 min. The histamine effect was completely inhibited by the H1 antagonist diphenhydramine (10(-6) mol/l), but not influenced by the H2 antagonist cimetidine (up to 10(-3) mol/l). When histamine was applied repeatedly in the absence of external calcium, the amplitude of the hyperpolarization decreased until finally no response was observed. Ba2+ (2 mmol/l) and quinidine (1 mmol/l), both inhibitors of potassium conductance, significantly reduced histamine-induced hyperpolarization. It was also reduced when cells were depolarized by 40 mmol/l extracellular potassium and almost completely abolished in the presence of 80 mmol/l external potassium. We conclude that H1 receptors mediate hyperpolarization by increasing potassium conductance, probably via transient release of intracellularly stored calcium.