Ca2+ influx through stretch-activated cation channels activates maxi K+ channels in porcine endocardial endothelium.
The endocardial endothelium is an important modulator of myocardial function. The present study demonstrates the existence of a stretch-activated Ca(2+)-permeable cation channel and of a Ca(2+)-activated K+ channel in the endocardial endothelium of the porcine right atrium. The stretch-activated channel is permeable for K+, Na+, Ca2+, and Ba2+, with mean conductances of approximately 32 pS for the monovalent cations and approximately 13 pS for divalent cations. The Ca(2+)-activated K+ channel has a mean conductance of 192 pS in symmetrical KCl. solution. Channel activity is strongly dependent on membrane potential and the cytosolic Ca2+ concentration. Half-maximal activation occurs at a cytosolic Ca2+ concentration of approximately 5 microM. The influx of Ca2+ through the stretch-activated channel is sufficient to activate the Ca(2+)-activated K+ channel in cell-attached patches. Upon activation of the stretch-activated channel, the cytosolic Ca2+ concentration increases, at least locally, to values of approximately 0.5 microM, as deduced from the open probability of the Ca(2+)-dependent K+ channel that was activated simultaneously. The stretch-activated channels are capable of inducing an intracellular Ca2+ signal and may have a role as mechanosensors in the atrial endothelium, possibly activated by atrial overload.
Hoyer
J
J
Universitätsklinikum Steglitz, Freie Universität Berlin, Germany.
Distler
A
A
Haase
W
W
Gögelein
H
H
D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D004699:Endocardium / Q000378:metabolism* / Q000648:ultrastructure; D004727:Endothelium / Q000378:metabolism / Q000648:ultrastructure; D007473:Ion Channels; D008564:Membrane Potentials; D008854:Microscopy, Electron; D015221:Potassium Channels / Q000378:metabolism*; D013552:Swine
D015220:Calcium Channels; D007473:Ion Channels; D015221:Potassium Channels; D002118:Calcium