Modulation of the activity of Ca(2+)-activated K+ channels by internal Mg2+ in cultured kidney cells vero.
The inside-out mode of the patch-clamp method was used to study the effects of internal Mg2+ on single large-conductance (193+/-7 pS) Ca(2+)-activated K+ channels in cultured kidney cells. In the absence of Ca2+, Mg2+ (1 to 10 mM) did not activate the channels but modified the activating effect of Ca2+ ions: it decreased the Hill coefficient (n), reduced the apparent dissociation constant (K0.5), and modified the channel open and closed times. K0.5 was found to be a voltage-dependent parameter. In the absence of Mg2+, it averaged 600 microM at -20 mV and 27 microM at +30 mV (22 degrees C, pH 6.8). Mg2+ at saturating concentrations (5 to 10 mM) decreased K0.5 to 50 microM at -20 mV and to 15 microM at +30 mV. Irrespective of the membrane potential, K0.5 tended to its limit value of about 12.6 microM. Thus, the effects of membrane depolarization and Mg2+ exhibited a non-additive, competitive relationship. Mg2+ perturbed the exponential shape of the voltage dependences of K0.5. The Hill coefficient characterizing the interaction of Ca2+ ions with the channels was found to be voltage-dependent. In the absence of Mg2+, it increased rather sharply from approx. 2 to 3.5 when the membrane potential was raised from -10 to 0 mV. Mg2+ increased n in a dose-dependent manner; however, about a twofold increase of n occurred within a narrow concentration range (2 to 3 mM). The action of Mg2+ on n was, apparently, voltage-independent, and the effects of Mg2+ and voltage on n were seemingly additive.
Kazachenko
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VN
Institute of Cell Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, Russia. kazachenko@icb.psn.ru
Chemeris
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NK
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D014709:Vero Cells
D015221:Potassium Channels; D008274:Magnesium; D002118:Calcium