Small-conductance Ca(2+)-activated K+ channels in bovine chromaffin cells.
Simultaneous whole-cell patch-clamp and fura-2 fluorescence [Ca2+]i measurements were used to characterize Ca(2+)-activated K+ currents in cultured bovine chromaffin cells. Extracellular application of histamine (10 microM) induced a rise of [Ca2+]i concomitantly with an outward current at holding potentials positive to -80 mV. The activation of the current reflected an increase in conductance, which did not depend on membrane potential in the range -80 mV to -40 mV. Increasing the extracellular K+ concentration to 20 mM at the holding potential of -78 mV was associated with inwardly directed currents during the [Ca2+]i elevations induced either by histamine (10 microM) or short voltage-clamp depolarizations. The current reversal potential was close to the K+ equilibrium potential, being a function of external K+ concentration. Current fluctuation analysis suggested a unit conductance of 3-5 pS for the channel that underlies this K+ current. The current could be blocked by apamin (1 microM). Whole-cell current-clamp recordings showed that histamine (10 microM) application caused a transient hyperpolarization, which evolved in parallel with the [Ca2+]i changes. It is proposed that a small-conductance Ca(2+)-activated K+ channel is present in the membrane of bovine chromaffin cells and may be involved in regulating catecholamine secretion by the adrenal glands of various species.
Artalejo
A R
AR
Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
García
A G
AG
Neher
E
E
D000311:Adrenal Glands / Q000502:physiology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000187:drug effects / Q000502:physiology*; D004553:Electric Conductivity; D006632:Histamine / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*
D015221:Potassium Channels; D001030:Apamin; D006632:Histamine; D002118:Calcium