Activation of a potassium outward current by zymosan and opsonized zymosan in mouse peritoneal macrophages.

The effects of zymosan and human serum opsonized zymosan on membrane currents of adherent mouse peritoneal macrophages which had been cultured for 5 to 20 days were investigated with the whole-cell voltage-clamp technique. Both stimuli activated an outward current. The outward current activation was transient and lasted about 5 min. In solutions with 10 or 50 mmol/l extracellular potassium concentration the activation of an outwardly directed current occurred at test potentials positive to the respective potassium equilibrium potential. This particle-induced current resembled a calcium-activated potassium current which could be activated with the calcium ionophore A 23187 and with platelet activating factor. The order of maximal responses (test potential + 55 mV, amplitude given as percentage of the respective control) was: 0.1 mumol/l platelet activating factor (222 +/- 36%, n = 8, P < 0.01) > 1 mumol/l A 23187 (190 +/- 24%, n = 11, P < 0.01) > 900 micrograms/ml opsonized zymosan (134 +/- 7%, n = 22, P < 0.01) > 900 micrograms/ml zymosan (116 +/- 5%, n = 21, P < 0.01). The lower efficiency of zymosan as compared to opsonized zymosan is explained in part by a lower percentage of responding cells which was 48% for zymosan and 73% for opsonized zymosan. Macrophages which were pretreated with particles showed a greater reactivity to calcium as compared to untreated cells.(ABSTRACT TRUNCATED AT 250 WORDS)