Calcium (Ca2+)-activated K+ (KCa) channels regulate membrane excitability and are activated by an increase in cytosolic Ca2+ concentration ([Ca2+]i), leading to membrane hyperpolarization. Most patch clamp experiments that measure KCa currents use steady-state [Ca2+] buffered within the patch pipette. However, when cells are stimulated physiologically, [Ca2+]i changes dynamically, for example during [Ca2+]i oscillations. Therefore, the aim of the present study was to examine the effect of dynamic changes in [Ca2+]i on small (SK3), intermediate (hIK1), and large conductance (BK) channels. HEK293 cells stably expressing each KCa subtype in isolation were used to simultaneously measure agonist-evoked [Ca2+]i signals, using indo-1 fluorescence, and current/voltage, using perforated patch clamp. Agonist-evoked [Ca2+]i oscillations induced a corresponding KCa current that faithfully followed the [Ca2+]i in 13–50% of cells, suggesting a good synchronization. However, [Ca2+]i and KCa current was much less synchronized in 50–76% of cells that exhibited Ca2+-independent current events (55% of SK3-, 50% of hIK1-, and 53% of BK-expressing cells) and current-independent [Ca2+]i events (18% SK3- and 33% of BK-expressing cells). Moreover, in BK-expressing cells, where [Ca2+]i and KCa current was least synchronized, 36% of total [Ca2+]i spikes occurred without activating a corresponding KCa current spike, suggesting that BKCa channels were either inhibited or had become desensitized. This desynchronization between dynamic [Ca2+]i and KCa current suggests that this relationship is more complex than could be predicted from steady-state [Ca2+]i and KCa current. These phenomena may be important for encoding stimulus–response coupling in various cell types.
The Journal of Membrane Biology – Springer Journals
Published: Jun 11, 2010
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