Chloride dependence of pH modulation by beta-adrenergic agonist in rat cardiomyocytes.
The effects of beta-adrenergic agonists on pHi were studied on single ventricular myocytes isolated from adult rat heart and loaded with the acetoxymethyl ester (AM) form of the pH indicator SNARF-1. In modified Krebs' solution containing 20 mmol/L HEPES and 4.4 mmol/L HCO3-, isoproterenol (1 mumol/L) caused a significant decrease of steady-state pHi from 7.20 +/- 0.02 to 7.13 +/- 0.02 (mean +/- SEM) within 2 minutes. This acidification, which was also observed in myocytes that were preloaded with the Ca2+ chelator BAPTA and superfused with nominally Ca(2+)-free solution, was blocked by propranolol as well as by the specific beta 1-antagonist CGP 20712 A but not by the beta 2-antagonist ICI 118,551. Forskolin (10 mumol/L) induced a similar reversible decrease of pHi (average decrease, 0.11 +/- 0.02 pH unit). Furthermore, adenosine (100 mumol/L) substantially attenuated the isoproterenol-induced decrease of pHi. The effect of isoproterenol was not prevented by inhibitors of the Na(+)-H+ antiport, amiloride (1 mmol/L) and 2-N,N-hexamethylene amiloride (20 mumol/L). On the other hand, blockers of Cl- transport mechanisms, DIDS (200 mumol/L) and probenecid (100 mumol/L), inhibited this acidification, Isoproterenol also failed to induce a decrease of steady-state pHi in myocytes incubated in Cl(-)-free medium. Rather, the initial rate of rise of pHi observed on removal of external Cl- ions was significantly increased in the presence of isoproterenol or dibutyryl cAMP. Because the alkalinization induced by removal of Cl- ions is mainly due to reversal of the Cl(-)-HCO3- exchanger, the augmentation of this initial rate of pHi rise directly points to a beta-adrenergic stimulation of the exchanger. Furthermore, the pHi recovery following NH4Cl exposure was accelerated by isoproterenol in the presence of probenecid, indicating that the Na(+)-HCO3- cotransport and/or the Na(+)-H+ antiport also could be activated.(ABSTRACT TRUNCATED AT 250 WORDS)
Désilets
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INSERM U-390, CHU Arnaud de Villeneuve, Montpellier, France.
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Vassort
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D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000187:drug effects / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D006352:Heart Ventricles / Q000166:cytology / Q000382:microbiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000502:physiology
D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D003994:Bucladesine; D000242:Cyclic AMP; D000241:Adenosine; D007545:Isoproterenol