Contribution of BK channels to action potential repolarisation at minimal cytosolic Ca super(2+) concentration in chromaffin cells
BK channels modulate cell firing in excitable cells in a voltage-dependent manner regulated by fluctuations in free cytosolic Ca super(2+) during action potentials. Indeed, Ca super(2+)-independent BK channel activity has ordinarily been considered not relevant for the physiological behaviour of exc...
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Veröffentlicht in: | Pflügers Archiv 2011-10, Vol.462 (4), p.545-557 |
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Sprache: | eng |
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Zusammenfassung: | BK channels modulate cell firing in excitable cells in a voltage-dependent manner regulated by fluctuations in free cytosolic Ca super(2+) during action potentials. Indeed, Ca super(2+)-independent BK channel activity has ordinarily been considered not relevant for the physiological behaviour of excitable cells. We employed the patch-clamp technique and selective BK channel blockers to record K super(+) currents from bovine chromaffin cells at minimal intracellular (about 10 nM) and extracellular (free Ca super(2+)) Ca super(2+) concentrations. Despite their low open probability under these conditions (V sub(50) of +146.8 mV), BK channels were responsible for more than 25% of the total K super(+) efflux during the first millisecond of a step depolarisation to +20 mV. Moreover, BK channels activated about 30% faster ( tau =0.55 ms) than the rest of available K super(+) channels. The other main source of fast voltage-dependent K super(+) efflux at such a low Ca super(2+) was a transient K super(+) (I sub(A)-type) current activating with V sub(50)=-14.2 mV. We also studied the activation of BK currents in response to action potential waveforms and their contribution to shaping action potentials both in the presence and the absence of extracellular Ca super(2+). Our results show that BK channels activate during action potentials and accelerate cell repolarisation even at minimal Ca super(2+) concentration, and suggest that they could do so also in the presence of extracellular Ca super(2+), before Ca super(2+) entering the cell facilitates their activity. |
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ISSN: | 0031-6768 1432-2013 |
DOI: | 10.1007/s00424-011-0991-9 |