Phenylphosphonate (PPA): a 31P-NMR indicator of extracellular pH and volume

31P-NMR has been used extensively to estimate intracellular (IC) pH for a variety of cells based on shifts in IC phosphate resonance frequencies. It also can be used to determine extracellular (EC) pH and fraction of total tissue volume (ECV) when a suitable NMR-sensitive EC phosphorous probe is used. The present study confirms that PPA is a noncytotoxic NMR detectable pH-sensitive marker confined to the EC space. concentrations of 2 to 12 mM do not affect either tension in rabbit bladder strips, or high energy phosphagen levels in the isolated perfused bladder. PPA resonates several parts per million downfield from endogenous phosphates, and is pH sensitive; its pK is 7.0 at 230C and its pH-dependent chemical shift is 1 ppm/pH unit over the pH range of 6.4 to 7.6. Using the isolated bladder with a perfusion flow of .372 ml/min, PPA (12 mM) washed in (PPA = 7.6e/sup .029t/; r = .84; n = 2) at the same rate it washed out (PPA = 50e/sup -.029t/; r = .96; n = 2). When perfusion flow was first .100 ml/min (for 90 mins), then .372 ml/min, PPA wash in and out rates were the same as before flow was lowered, indicating a single compartment, even though an expanded one. ECV was 0.34 +/- .029 (anti x +/- SEM); n = 3) and 0.54 +/- .041 (n = 3), for before and after low flow, respectively. PPA is a 31P-NMR detectable agent for both EC pH and ECV in both normal and metabolically impaired tissues