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

Background and purpose:

Intracellular pH (pH_i) in heart is regulated by sarcolemmal H⁺‐equivalent transporters such as Na⁺‐H⁺ exchange (NHE) and Na⁺‐HCO₃⁻ 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 (C₂₉H₂₄ClN₃O₃S) 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.

Experimental approach:

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 CO₂/HCO₃⁻‐buffered superfusates containing 30 μM cariporide (to inhibit NHE), pH_i recovery is mediated by NBC.

Key results:

S0859, an N‐cyanosulphonamide compound, reversibly inhibited NBC‐mediated pH_i recovery (K_i=1.7 μM, full inhibition at ∼30 μM). In HEPES‐buffered superfusates, NHE‐mediated pH_i recovery was unaffected by 30 μM S0859. With CO₂/HCO₃⁻ buffer, pH_i recovery from intracellular alkalosis (mediated by Cl⁻/HCO₃⁻ and Cl⁻/OH⁻ exchange) was also unaffected. Selective NBC‐inhibition was not due to action on carbonic anhydrase (CA) enzymes, as 100 μM 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.

Conclusions and implications:

Compound S0859 is a selective, high‐affinity generic NBC inhibitor, potentially important for probing the transporter's functional role in heart and other tissues.

DOI: 10.1038/sj.bjp.0707667

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