{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,27]],"date-time":"2025-10-27T10:45:56Z","timestamp":1761561956828},"reference-count":33,"publisher":"American Physiological Society","issue":"2","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["American Journal of Physiology-Heart and Circulatory Physiology"],"published-print":{"date-parts":[[2002,8,1]]},"abstract":"<jats:p> Sudden increases in heart rate cause accumulation of K<jats:sup>+<\/jats:sup> in the extracellular space. However, the exact relationship between rate and extracellular K<jats:sup>+<\/jats:sup> concentration ([K<jats:sup>+<\/jats:sup>]<jats:sub>o<\/jats:sub>) in vivo is unknown. We measured [K<jats:sup>+<\/jats:sup>]<jats:sub>o<\/jats:sub> in right atria of anesthetized dogs by using K<jats:sup>+<\/jats:sup>-sensitive electrodes. Peak increase in [K<jats:sup>+<\/jats:sup>]<jats:sub>o<\/jats:sub> ranged from 0.18 \u00b1 0.04 mM [means \u00b1 SE; cycle length (CL) = 350 ms] to 0.80 \u00b1 0.09 mM (CL = 250 ms) above baseline (3.50 \u00b1 0.08 mM at CL = 380 ms; n = 5). During rapid pacing-induced atrial fibrillation, peak increase in [K<jats:sup>+<\/jats:sup>]<jats:sub>o<\/jats:sub>averaged 0.80 \u00b1 0.07 mM ( n = 5). Whole cell current-clamp measurements in single right atrial myocytes ( n = 5) showed that raising [K<jats:sup>+<\/jats:sup>]<jats:sub>o<\/jats:sub> from 3 to 5 mM in 1-mM steps progressively depolarized resting membrane potential and reduced both phase 0 action potential amplitude and maximal upstroke velocity. Multisite epicardial mapping ( n = 4) demonstrated that sudden rate increases changed longitudinal conduction velocity (CV<jats:sub>L<\/jats:sub>) by \u22123.6 \u00b1 1.8% to \u22125.9 \u00b1 1.2% over a CL range of 330 to 250 ms. Our observations suggest that rate-related [K<jats:sup>+<\/jats:sup>]<jats:sub>o<\/jats:sub> accumulation in vivo is of sufficient magnitude to modulate those cellular electrophysiological properties that determine atrial CV<jats:sub>L<\/jats:sub>. <\/jats:p>","DOI":"10.1152\/ajpheart.00721.2001","type":"journal-article","created":{"date-parts":[[2015,3,3]],"date-time":"2015-03-03T15:03:14Z","timestamp":1425394994000},"page":"H506-H517","source":"Crossref","is-referenced-by-count":13,"title":["Rate-dependent [K<sup>+<\/sup>]<sub>o<\/sub> accumulation in canine right  atria in vivo: electrophysiological consequences"],"prefix":"10.1152","volume":"283","author":[{"given":"Akira","family":"Miyata","sequence":"first","affiliation":[{"name":"Krannert Institute of Cardiology, Indianapolis, Indiana 46202"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Joshua D.","family":"Dowell","sequence":"additional","affiliation":[{"name":"Krannert Institute of Cardiology, Indianapolis, 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