An electrogenic sodium-bicarbonate cotransport in the regulation of myocardial intracellular pH.
Experiments were performed in cat papillary muscles in order to explore the possible existence of an electrogenic Na+/HCO3- cotransport. Developed tension (DT), intracellular pH (pHi) with the pH-sensitive dye 2'-7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF) and resting membrane potential (Vm) with 3M KCl filled glass microelectrodes were measured. A change from HEPES to HCO3(-)-buffered superfusate induced an immediate decrease in pHi and DT followed by a recovery in which pHi and DT stabilized at values slightly higher than in HEPES buffer. Introduction of HCO3- hyperpolarized Vm by 8 +/- 2.3 mV (P < 0.05). SITS (0.1 mM) completely abolished the hyperpolarization and attenuated the recovery of both pHi and DT. Under steady-state conditions in HCO3- buffered media, SITS induced a depolarization compatible with the suppression of the entry of negative charges. Depolarization by high Ko+ (45 mM) elicited a rise in pHi of 0.07 +/- 0.02 (P < 0.05), that was reversed by returning Ko+ to normal. The depolarization-induced rise in pHi proved to be Na(+)-dependent, SITS sensitive and still occurred after EIPA (microM) blockade. All the evidence strongly supports the existence of an electrogenic Na+/HCO3- cotransport mechanism that participates in the regulation of myocardial pHi. At pHi of 6.94 this mechanism seems to contribute almost equally to the Na+/H+ exchanger to pHi regulation. However, acid equivalent extrusion is potentiated when both the Na+/H+ exchanger and the HCO3-dependent mechanism are simultaneously regulating pHi.
Camilión de Hurtado
M C
MC
Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Argentina.
Pérez
N G
NG
Cingolani
H E
HE
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002415:Cats; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D010210:Papillary Muscles / Q000378:metabolism / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters; D013997:Time Factors
D000889:Anti-Arrhythmia Agents; D001639:Bicarbonates; D002352:Carrier Proteins; D027982:Sodium-Bicarbonate Symporters; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D012964:Sodium; D011188:Potassium; C039614:ethylisopropylamiloride