Role of an electrogenic Na+-HCO3- cotransport in determining myocardial pH(i) after an increase in heart rate

María C. Camilión de Hurtado, Bernardo V. Alvarez, Néstor G. Pérez, Horacio E. Cingolani

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


The contribution of electrogenic Na+-HCO3- cotransport to pH(i) regulation during changes in heart rate was explored in cat papillary muscles loaded with BCECF-AM in bicarbonate free (HEPES) medium and in CO2/HCO3- buffered medium. Stepwise increments in the frequency of contraction from 15 to 100 bpm induced a reversible increase in the pH(i) from 7.13±0.03 to 7.36±0.03 (P<0.5, n=5) in the presence of CO2/HCO3- buffer. The same increase in the frequency of stimulation, however, decreased pH(i) from 7.10±0.02 to 6.91±0.06 (P<.05, n=5), in the absence of bicarbonate. Moreover, in CO2/HCO3--superfused muscles pretreated with SITS (0.1 mmol/L), this effect of increasing the contraction frequency was reversed, and a decrease of pH1, from 7.03±0.04 to 6.88±0.06 (P<.05, n=4) was observed when the pacing rate was increased stepwise from 15 to 100 bpm. High [K+](o)-induced depolarization of cell membrane alkalinized myocardial cells in the presence of HCO3- ions, whereas acidification was observed as a consequence of hyperpolarization induced by low external [K+](o). Myocardial resting membrane potential became hyperpolarized upon exposure to HCO3-- buffered media. This HCO3--induced hyperpolarization was not blocked by the inhibition of Na+,K+-ATPase activity by ouabain (0.5 μmol/L) but was prevented by SITS. The results suggested that membrane depolarization during cardiac action potential causes an increase in electrogenic Na+-HCO3- cotransport. Such depolarizations occurring as a consequence of increases in heart rate would thus, by means of elevated bicarbomate influxes, substantially increase the myocardial cell's ability to recover from an enhanced proton production.

Original languageEnglish (US)
Pages (from-to)698-704
Number of pages7
JournalCirculation research
Issue number4
StatePublished - 1996
Externally publishedYes


  • Na-HCO cotransport
  • heart rate
  • membrane potential
  • pH(i)

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine


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