Histamine lipolysis II: effects of histamine and related compounds on membrane potentials of rat adipocytes.

The effects of histamine (Hi) and related compounds on rat mesenterial adipocytes were investigated using electrophysiological techniques. Hi caused a concentration-related depolarization and significant effect was observed at concentrations higher than 5 x 10(-6) M. Effective membrane resistance was also decreased by Hi. The H1-agonists 2-methylHi and 2-thiazolylethylamine caused no depolarization even at a concentration of 5 x 10(-4) M, but the H2-agonists, 4-methylHi and impromidine decreased resting membrane potentials. While 4-methylHi was less potent than Hi, impromidine was more potent. The H1-antagonists diphenhydramine and pyrilamine did not affect Hi-induced depolarization. However, H2-antagonists like cimetidine and ranitidine caused a significant inhibition even at a concentration of 10(-6) M. As in the case of isoproterenol, the decrease in resting membrane potentials induced by Hi was significantly potentiated by theophylline. Dibutyryl cyclic AMP treatment and intracellular application of cyclic AMP also caused a marked depolarization.