Ca2+ and Mn2+ influx through receptor-mediated activation of nonspecific cation channels in mast cells.
Whole-cell patch-clamp recordings of membrane currents and Fura-2 measurements of free intracellular calcium concentration ([Ca2+]i) were used to study calcium influx through receptor-activated cation channels in rat peritoneal mast cells. Cation channels were activated by the secretagogue compound 48/80, whereas a possible concomitant Ca2+ entry through pathways activated by depletion of calcium stores was blocked by dialyzing cells with heparin. Heparin effectively suppressed the transient Ca2+ release induced by 48/80 and abrogated inositol 1,4,5-trisphosphate-induced calcium influx without affecting activation of 50-pS cation channels. There was a clear correlation between changes in [Ca2+]i and the activity of 50-pS channels. The changes in [Ca2+]i increased with elevation of extracellular Ca2+. At the same time, inward currents through 50-pS channels were diminished as more Ca2+ permeated. This effect was due to a decrease in slope conductance and a reduction in the open probability of the cation channels. In physiological solutions, 3.6% of the total current was carried by Ca2+. The cation channels were not only permeable to Ca2+ but also to Mn2+, as evidenced by the quench of Fura-2 fluorescence. Mn2+ current through 50-pS channels could not be resolved at the single-channel level. Our results suggest that 50-pS cation channels partially contribute to sustained increases of [Ca2+]i in mast cells following receptor activation.
Fasolato
C
C
Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.
Hoth
M
M
Matthews
G
G
Penner
R
R
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002412:Cations; D016257:Fura-2; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008345:Manganese / Q000378:metabolism*; D008407:Mast Cells / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000502:physiology*; D013050:Spectrometry, Fluorescence; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology
D002412:Cations; D007473:Ion Channels; D011956:Receptors, Cell Surface; D003189:p-Methoxy-N-methylphenethylamine; D008345:Manganese; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium; D016257:Fura-2