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  • Title: Effect of histamine on the membrane potential of cultured human nonpigmented ciliary epithelial cells.
    Author: Stahl F, Garus HJ, Lepple-Wienhues A, Wiederholt M.
    Journal: Ger J Ophthalmol; 1992; 1(1):62-6. PubMed ID: 1477621.
    Abstract:
    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.
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