Cytoskeletal control of rectification and expression of four substates in cardiac inward rectifier K+ channels.
Cardiac inward rectifiers may have a three-barrel channel structure, based on evidence for three substates in single-channel recordings. However, some reports indicate four substates, a feature more compatible with the four-subunit structure for which there is evidence in cloned voltage-activated K+ channels. Here we show that although the fourth is easily missed, inward rectifier channels have four substates whose expression is controlled by intracellular Ca(2+) ions. Fourth substate openings also appear after rectification loss in intracellular divalent caution-free solution. We find that this process is accelerated by cytochalasin, a microfilament disrupter. Cytochalasin also abolishes Ca(2+), but not Mg(2+),-induced rectification by restoring fourth substate openings. Thus, cytoskeletal elements control Ca(2+)-dependent substate expression and rectification in native inwardly rectifying K+ channels.
Mazzanti
M
M
Dipartimento di Fisiologia e Biochimica Generali, Universita di Milano, Italy.
Assandri
R
R
Ferroni
A
A
DiFrancesco
D
D
D000818:Animals; D002118:Calcium / Q000378:metabolism; D003599:Cytoskeleton / Q000502:physiology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology*
D015221:Potassium Channels; D008274:Magnesium; D002118:Calcium