S0859, an N‐cyanosulphonamide inhibitor of sodium‐bicarbonate cotransport in the heart

Abstract

Intracellular pH (pH(i)) in heart is regulated by sarcolemmal H(+)-equivalent transporters such as Na(+)-H(+) exchange (NHE) and Na(+)-HCO(3) (-) cotransport (NBC). Inhibition of NBC influences pH(i) and can be cardioprotective in animal models of post-ischaemic reperfusion. Apart from a rabbit polyclonal NBC-antibody, a selective NBC inhibitor compound has not been studied. Compound S0859 (C(29)H(24)ClN(3)O(3)S) is a putative NBC inhibitor. Here, we provide the drug's chemical structure, test its potency and selectivity in ventricular cells and assess its suitability for experiments on cardiac contraction. pH(i) recovery from intracellular acidosis was monitored using pH-epifluorescence (SNARF-fluorophore) in guinea pig, rat and rabbit isolated ventricular myocytes. Electrically evoked cell shortening (contraction) was measured optically. With CO(2)/HCO(3) (-)-buffered superfusates containing 30 muM cariporide (to inhibit NHE), pH(i) recovery is mediated by NBC. S0859, an N-cyanosulphonamide compound, reversibly inhibited NBC-mediated pH(i) recovery (K (i)=1.7 microM, full inhibition at approximately 30 microM). In HEPES-buffered superfusates, NHE-mediated pH(i) recovery was unaffected by 30 microM S0859. With CO(2)/HCO(3) (-) buffer, pH(i) recovery from intracellular alkalosis (mediated by Cl(-)/HCO(3) (-) and Cl(-)/OH(-) exchange) was also unaffected. Selective NBC-inhibition was not due to action on carbonic anhydrase (CA) enzymes, as 100 microM acetazolamide (a membrane-permeant CA-inhibitor) had no significant effect on NBC activity. pH(i) recovery from acidosis was associated with increased contractile-amplitude. The time course of recovery of pH(i) and contraction was slowed by S0859, confirming that NBC is a significant controller of contractility during acidosis. Compound S0859 is a selective, high-affinity generic NBC inhibitor, potentially important for probing the transporter's functional role in heart and other tissues.