Novel cation-selective mechanosensitive ion channel in the atrial cell membrane.

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Abstract
Stretch of atrial muscle causes the release of atrial natriuretic peptide, but no stretch-sensitive membrane sensors have been clearly identified so far. The existence of an ion channel that could mediate stretch-induced Ca2+ influx and subsequent release of the peptide was examined in rat atrial cells. In this report, the discovery of a novel atrial ion channel whose opening probability is extremely sensitive to either positive or negative pressure (half-maximal activation pressure, approximately 1.5 mm Hg) is described. Activation of the current by pressure applied to the pipette was observed both at the whole-cell and single-channel levels. The channel was permeable to cations including Ca2+. The channels were clustered with six to nine channels in each cluster, and several channels tended to open simultaneously in response to a graded increase in pressure for the inwardly passing current. Hypotonic swelling also activated these channels. These results show that mechanosensitive nonselective cation channels exist in atrial cells and suggest that they could be involved in beat-to-beat regulation of the atrial contraction as well as the stretch-induced expression of proto-oncogenes and secretion of atrial natriuretic peptide via increased Ca2+ entry.