Coupling of Dual Acid Extrusion in the Guinea-pig Isolated Ventricular Myocyte to Alpha 1- and Beta-adrenoceptors

1. Intracellular pH (pHi) was recorded in single, isolated guinea-pig ventricular myocytes using the pH-sensitive fluorophore, carboxy-SNARF-1 (AM-loaded). 2. The dual acid extrusion system in this cell (Na(+)-H+ antiport and Na(+)-HCO3- symport) was activated by inducing an intracellular acid load, produced by addition and subsequent removal of extracellular 10 mM NH4Cl. Under these conditions, it is known that both acid-equivalent extruders are activated about equally. 3. Application of phenylephrine (100 microM; alpha-adrenergic agonist) resulted in an inhibition of pHi recovery from an acid load, recorded in HCO3-buffered medium containing 1.5 mM amiloride (amiloride inhibits Na(+)-H+ antiport; under these conditions pHi recovery is mediated through only the Na(+)-HCO3- symport carrier). This inhibitory effect of phenylephrine was prevented by the alpha 1-antagonist, prazosin (0.1 microM) and was unaffected by propranolol (1 microM). 4. Application of phenylephrine in Hepes-buffered medium (only Na(+)-H+ antiport is active under these conditions) elicited a stimulation of pHi recovery, again prevented by prazosin (0.1 microM). 5. These results point to an alpha 1 inhibition of Na(+)-HCO3- symport and an alpha 1 stimulation of Na+-H+ antiport. 6. Both adrenaline (1-5 microM) and noradrenaline (5 microM) slowed pHi recovery recorded in HCO3(-)-buffered solution containing amiloride (1.5 mM). The similarity of this result with that obtained previously using phenylephrine (paragraph 3) suggests that all three agonists inhibit the Na(+)-HCO3- symport through alpha 1 activation. 7. Isoprenaline (1 microM; beta-adrenergic agonist) slowed pHi recovery in Hepes-buffered solution but stimulated recovery in a HCO3(-)-buffered solution containing amiloride (1.5 mM). These results suggest that beta activation slows Na(+)-H+ antiport but stimulates Na(+)-HCO3- symport. 8. When both acid-equivalent extrusion carriers were inhibited in Na(+)-free, HCO3(-)-buffered medium, phenylephrine or isoprenaline had no effect on pHi, ruling out any effect of the adrenergic agonists on background acid-loading mechanisms. 9. Under physiological conditions (CO2/HCO3(-)-buffered solution, no amiloride), when both acid extruders would be activated by an intracellular acid load, application of phenylephrine, adrenaline or noradrenaline were found to slow pHi recovery. In contrast, isoprenaline stimulated pHi recovery under the same conditions.(ABSTRACT TRUNCATED AT 400 WORDS)