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Ca 2+ sparks activate K + and Cl − channels, resulting in spontaneous transient currents in guinea‐pig tracheal myocytes
Author(s) -
ZhuGe Ronghua,
Sims Stephen M.,
Tuft Richard A.,
Fogarty Kevin E.,
Walsh John V.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.711ba.x
Subject(s) - depolarization , chemistry , biophysics , membrane potential , cytosol , myocyte , patch clamp , bk channel , reversal potential , conductance , intracellular , guinea pig , ryanodine receptor , ion channel , biochemistry , physics , endocrinology , biology , receptor , condensed matter physics , enzyme
1 Local changes in cytosolic [Ca 2+ ] were imaged with a wide‐field, high‐speed, digital imaging system while membrane currents were simultaneously recorded using whole‐cell, perforated patch recording in freshly dissociated guinea‐pig tracheal myocytes. 2 Depending on membrane potential, Ca 2+ sparks triggered ‘spontaneous’ transient inward currents (STICs), ‘spontaneous’ transient outward currents (STOCs) and biphasic currents in which the outward phase always preceded the inward (STOICs). The outward currents resulted from the opening of large‐conductance Ca 2+ ‐activated K + (BK) channels and the inward currents from Ca 2+ ‐activated Cl − (Cl Ca ) channels. 3 A single Ca 2+ spark elicited both phases of a STOIC, and sparks originating from the same site triggered STOCs, STICs and STOICs, depending on membrane potential. 4 STOCs had a shorter time to peak (TTP) than Ca 2+ sparks and a much shorter half‐time of decay. In contrast, STICs had a somewhat longer TTP than sparks but the same half‐time of decay. Thus, the STIC, not the STOC, more closely reflected the time course of cytosolic Ca 2+ elevation during a Ca 2+ spark. 5 These findings suggest that Cl Ca channels and BK channels may be organized spatially in quite different ways in relation to points of Ca 2+ release from intracellular Ca 2+ stores. The results also suggest that Ca 2+ sparks may have functions in smooth muscle not previously suggested, such as a stabilizing effect on membrane potential and hence on the contractile state of the cell, or as activators of voltage‐gated Ca 2+ channels due to depolarization mediated by STICs.